Mercury species in zooplankton, brine, and bottom sediments of hyperhaline Lake Bolshoye Yarovoye (south of Western Siberia)

Mercury species in zooplankton, brine, and bottom sediments of hyperhaline Lake Bolshoye Yarovoye (south of Western Siberia) | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Mercury species in zooplankton, brine, and bottom sediments of hyperhaline Lake Bolshoye Yarovoye (south of Western Siberia) Mariya Gustaytis, Anton Maltsev, Galina Leonova, Sergei Krivonogov This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6909634/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 24 Dec, 2025 Read the published version in Environmental Earth Sciences → Version 1 posted 10 You are reading this latest preprint version Abstract The investigation focused on examining the concentration of mercury in the brine, plankton, and bottom sediments of Lake Bolshoye Yarovoye. Mercury in inorganic complexes primarily exists in the forms of HgCl 4 2– and Hg(SR) 2 . Within lake and pore waters, mercury will be present as MeHgSR-DOM rather than MeHgCl. Accumulation of mercury in bottom sediments ensues from the precipitation/dissolution processes oxides and oxyhydroxides of Fe and Mn. The geochemical behavior of mercury in sediments is subject to the influence of various sulfur compounds, including S (VI), S (II), S 0 , and pyrite, which possess the capacity to constrain the bioavailability of mercury and impact the formation of MeHg. A correlation is noted in the distribution of Hg-OM and S (II) within the upper 50 cm of sediment. The vertical migration of technogenic mercury in the sediment core due to its high water content has been identified. At a depth of 110–120 cm, a geochemical barrier emerges, characterized as a zone of active transformation of mercury forms. A moderate level of mercury contamination has been observed in bottom sediments and plankton Artemia salina within the influence zone of the “Altaikhimprom” plant. Mercury Methylmercury Mercury species Sulfur Mercury biogeochemistry Hyperhaline lake Western Siberia Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction Mercury is a highly toxic element and has the ability to bioaccumulate. Mercury has the highest ionization potential and a wide variety of chemical forms Hg in the environment. The potential risk and bioavailability of mercury for aquatic organisms directly depends on its chemical forms in aqueous solution and bottom sediments (Mason et al. 1993; Hai Luu Duc et al. 2010). Compounds of mercury with low-molecular-weight organic ligands, such as methylmercury, or free hydrated ions, exhibit a cumulative effect and higher stability in the aquatic environment. These forms of mercury are more toxic than inorganic forms of Hg. The methylated form of mercury has the most negative impact on aquatic biota (UNEP 2019). In water bodies, mercury accumulates in the surface layers of bottom sediments and can be included in various links of trophic chains (Zhu et al. 2018; Branfireun et al. 2020). Chemical compounds of mercury can accumulate both in aquatic organisms and in bottom sediments. In bottom sediments, mercury is transformed from an inorganic form to a methylated form (Fleck et al. 2016; Dórea et al. 2023). Judgments about the toxicity of mercury are based on its forms in bottom sediments rather than on the total concentration. Bottom sediments are used as indicators of water ecosystem pollution. Due to the high toxicity of mercury compounds to living organisms there is a greater relevance for comprehensive biogeochemical studies, allowing us to trace the migration paths of Hg in various components of the biosphere. These studies allow tracking the migration pathways of mercury in various components of the biosphere. The peculiarities of mercury migration and its bioaccumulation under natural and anthropogenic conditions in the south of Western Siberia are examined using the example of the impact of the chemical production facility of “Altaikhimprom”. Until 2014, the chemical plant was a major producer of chemical reagents in Russia, including two crystalline modifications of mercury oxides HgO (yellow and red), for the production of which metallic mercury was used as raw material. “Altaikhimprom” is located in the Altai region of Russia, near the town of Yarovoye, on the shore of the hyperhaline (salty) Lake Bolshoe Yarovoe. Salt lakes are particularly susceptible to anthropogenic influence as they lack surface and groundwater outflows. High mineralization of water and reducing conditions at depth do not contribute to the precipitation of heavy metals, which leads to their accumulation in salt lakes (Wurtsbaugh et al. 2020). Most salt lakes are characterized by a specific halophilic biota, often represented by various branchiopods, which can also concentrate large amounts of heavy metals. As a result of the death of branchiopods and their microbiological processing in salt lakes, organic muds, or therapeutic sulfide muds (peloids), are formed. They can accumulate heavy metals that come from the biota. The hyperhaline Lake Bolshoye Yarovoye is a large balneological resort and physiotherapeutic mud baths (Egorkina and Bender 2012). Our previous studies have demonstrated that the chemical plant “Altaikhimprom”, located on the shore of the lake, has created an unfavorable environmental situation in the near zone of its influence. According to our long-term research, the main diffuse sources of anthropogenic mercury input into the lake were the coastal dumps of solid mercury-containing waste from the plant, especially during the snowmelt period, which is consistent with the findings of other researchers (Temerev et al. 2002). A universal method that would allow the determination of all forms of mercury in brine (including organic form) has not yet been proposed due to the complexity of the composition of brine. Mercury compounds in environmental objects are determined using combined methods. They are multi-stage processes. These processes include the stage of preliminary extraction of the compounds being determined into a solution or gas phase. They are then separated by liquid (gas) chromatography or capillary electrophoresis followed by element-selective detection, usually by atomic spectrometric methods. In the analysis of solid natural samples, a necessary step is the preliminary transfer of analytes into solution by extraction or sorption. At this stage, losses of the determined forms are often observed, as well as their transformation from one form to another (Shuvaeva et al. 2008). Currently, the most promising method should be recognized as a direct hybrid method for the determination of inorganic compounds of mercury (II), monomethylmercury and mercury sulfide in solid samples. The method combines thermal analysis with atomic absorption detection, based on the differences in evaporation temperatures for various mercury compounds (Shuvaeva et al. 2008; Gustaytis et al. 2021). At present, the vertical distribution of mercury forms in hyperhaline environments has not been studied well enough. Thus, the goal of the work is to identify the characteristics of the concentration and distribution of chemical forms of mercury in plankton, brine and along the vertical profile of bottom sediments of the hyperhaline Lake Bolshoye Yarovoye using the direct hybrid method for determining Hg compounds. The study based on several objectives: i. To establish the distribution of mercury in brine and plankton; ii. To determine the forms of mercury in biota, water and sediments; iii. To establish the degree of pollution of the bottom sediments of Lake Bolshoe Yarovoe after the closure of the “Altaikhimprom” enterprise; iv. To identify the features of the concentration and distribution of mercury forms along the vertical profile of bottom sediments using the direct hybrid method for determining Hg compounds (such work has not been carried out in the region); v. To determine the causes of the transformation of mercury forms in the brine—plankton—bottom sediments system. 2. Materials and methods 2.1. Physiographic background and site description Lake Bolshoe Yarovoe occupies a deep depression (approximately 25 m) in the western part of the Kulunda Plain of the Ob-Irtysh interfluve (Altai Territory, southern West Siberia). The lake is located 6 km southwest of the town of Slavgorod (Fig. 1a, b). The northern and northeastern shores of the lake are gentle, rising 1.5–2.0 m above the water level (Fig. 1c). The southwestern shores of the lake are steep, reaching heights of up to 20 m. The lake is situated at an elevation of approximately 84 m above sea level. The length of the lake is 11 km and the width is 7.9 km. The water area of the lake is 70 km 2 , with an average depth of 4 m and a maximum depth of around 8 m (Rudaya et al. 2012). Lake Bolshoye Yarovoye is one of the deepest at the Kulunda Plain. The surrounding plain provides aeolian material input to the lake. The lake shoreline is not indented. Such relief characteristics result in the deposition of terrigenous material into the lake during spring runoff and precipitation events (Kosareva et al. 2020). The lake is not fed by rivers. Positive water balance is maintained through spring runoff from the watershed, groundwater seepage from steep shores, and winter and summer precipitation. Negative water balance is attributed to evaporation. Intense evaporation and low precipitation rates in the region led to a high degree of water salinity (Malikova et al. 2008). The high salinity of the water contributes to the development of specific biota in the lake, which is represented by halophilic species such as the branchiopod crustacean Artemia salina L. Lake Bolshoye Yarovoye is one of the most promising lakes in the region for harvesting A. salina . Industrial procurement of artemia has been carried out since 1978. Over the past 20 years, the volume of artemia procurement has increased from 14 to 483 tons. The “Altaikhimprom” chemical plant located on the northern shore of the lake and mercury-containing waste located in the northeastern part of the lake (Fig. 1c) is a source of accumulation of mercury in brine and in A. salina . 2.2. Water and sediment sampling Sampling of zooplankton ( Artemia salina) , brine and well drilling were carried out at the end of August 2022 in the central part of the lake (coordinates: N 52.86923° and E 78.60915°) (Fig. 1c). The brine was sampled with a bathometer throughout the entire depth of the lake in the epilimnion (0.5), metalimnion (4.0) and hypolimnion (8.2 m). Unconsolidated sediment (bottom sediments that is loosely arranged and unstratified) was collected using a bathometer in the bottom water layer. A. salina was sampled using the small plankton net. Plankton samples were weighed, then dried to an air-dry state and transported to the laboratory. The bottom sediments cores were collected in the central part of the lake (Fig. 1c). The coring operations were carried out from an inflated pontoon with a load of 5 tons using a Livingston -type piston sampler driven by vibration technology (Krivonogov et al. 2012). The sampler enables sequential retrieving of undisturbed lots of the core that are 2 m in length and 7.5 cm in diameter. The total core length was 4.83 m. The core was divided into 2–3 cm layers for geochemical studies. The cores obtained were measured for pH and Eh with the Anion 4100 ionometer (Infrapack-Analit, Russia), wrapped in plastic film, placed in tight plastic boxes, and transported to Novosibirsk for investigation. The lots were split in halves and documented. One half was used for pore water extraction and the other half was used for all other methods. Pore water was squeezed out of 10-cm pieces of the core into tight syringes, protected from oxygen supply according to the standard method (Jahnke , 1988) with the Omec PI.88.00 hydraulic press (Omec S.n.c., Mugio, Italy). Samples of the lake water were collected at the coring place by a bathometer near surface and near bottom. Temperature, pH, and Eh were immediately measured in the samples with an Anion 4100 ionometer. Raw water samples were used for hydrochemical analysis, and for elemental analysis, the water was vacuum-filtered through 0.45 µm filters and packed in plastic bottles with the addition of concentrated nitric acid (1 ml L –1 ) for preservation. 2.3. Analytical methods Concentrations of anions in the lake and pore water samples were determined by capillary zone electrophoresis (CZE) (Cl – , SO 4 2– , PO 4 3– ), on Agilent 7100 (Agilent Technologies, USA). Elements (Fe, Mn) in pore water and bottom sediments were measured by atomic emission spectroscopy with inductively coupled plasma (ICP-AES), on IRIS Advantage ICP-AES spectrometer (Thermo Jarrell Ash Corp., Franklin, MA, USA). Authigenic components (carbonates) were estimated by their successive removal with HCl, and the terrigenous mineral part was the residue. Total dissolved carbon (TDC) and proportions of dissolved inorganic and organic carbon (DIC and DOC, respectively) in water were determined on an AG Multi N/C 2100S analyzer (Analytik Jena GmbH, Jena, Germany). TDC was estimated by the amount of CO 2 released from samples after catalytic oxidation at 950° in the presence of oxygen flux in a quartz reactor. DIC was estimated by the amount of CO 2 released from samples after digestion in 10% H 3 PO 4 . DOC was found as the difference between TDC and DIC. Total organic carbon (TOC) was determined by Tyurin’s method. The method is based on the oxidation of organic matter with chromic acid to form carbon dioxide (Vorobyova, 1998). Contents of H, N, and S were measured on an automatic CHNS analyzer Euro EA 3000 (EuroVector S.p.A., Milan, Italy) following Fadeeva et al. (2008). The speciation of sulfur in sediment samples, total sulfur (S total ), sulfate (S (VI)), and sulfide (S (II)), was studied with ICP-AES. S total was determined by high-temperature digestion in HNO 3 under a lid and then by digestion in HCl, which transforms sulfide into sulfate. S (II) was removed from specimens via digestion in diluted HCl and subsequent filtering of the residue, whereby only sulfate sulfur remained. The amount of S (II) was estimated as the difference between S total and S (VI). Mineral composition of the sediments was analyzed by the X-ray powder diffraction (XRD) method on a DRON-4 diffractometer (Cu-Kα radiation), at the Analytical Center for Multielement and Isotope Studies of the Institute of Geology and Mineralogy SB RAS. Morphology of mineral grains and their element composition were studied in selected samples by scanning electron microscopy (SEM) on a Tescan Mira 3 LMU microscope according to Goldstein et al. (1981). The sediments were 14 C dated by accelerator mass-spectrometry (AMS) method in the Center of Collective Use “Cenozoic geochronology” of SB RAS, Novosibirsk. The dates were calibrated and converted into calendar years using the CALIB 8.2 [WWW program] at http://calib.org. 2.4. Chemical analyses of mercury Lake and pore water samples were filtered through cellulose acetate membrane filters (GVS Filter Technology, USA) with a pore size of 0.45 µm (Howe and Clark 2002). Two fractions of mercury were obtained: dissolved + colloidal (Hg-dc) and suspended (Hg-susp). Each of the fractions was analyzed of mercury species: reactive mercury (Hg-R) and non-reactive mercury (Hg-NR). According to Lindqvist and Rodhe (1985), the reactive forms of mercury include Hg 2+ , HgX, HgX; and HgXi- with X = OH – , Cl – and Br – ; suspended HgO; complexes of Hg 2+ with organic acids; Non-reactive forms include CH, Hg + , CH, HgCl; CH, HgOH and other organomercury compounds, Hg(CN); HgS and Hg 2+ associated with sulfur in organic matter. Reactive/non-reactive (or inorganic/organic) mercury can be determined in various ways (Bloom et al. 2003; Umezaki and Iwamoto 1971), by successively leaching groups of compounds at each step, as in the sequential leaching procedures (Bloom et al. 2003). In the absence of reliable chemical methods for separation of organic and inorganic mercury, we used the Hg-R vs. Hg-NR rather than organic vs. inorganic division (Lindqvist and Rodhe 1985). Determination of total mercury in plankton, brine, bottom sediments, and pore waters was carried out using atomic absorption spectrometry RA-915M (Lumex, Russia). Mercury contents in bottom sediments and pore waters were obtained down to a depth of 310 cm. Both unfiltered and filtered water samples for Hg assays were initially preconditioned using 1.5 mL of a 1:1 HNO 3 + H 2 SO 4 mixture added to 50 mL of sampled water. Then the solution, with 3–4 drops of 5% KMnO 4 , was left overnight; excess KMnO 4 was removed with 10% hydroxylamine-sulfate (NH 2 OH) 2 •H 2 SO 4 added drop-by-drop until the solution became clear. Oxidation and extraction of mercury with KMnO 4 is commonly applied to environmental samples (Agemian and Chau 1976; Myagkaya et al. 2022). Reactive mercury species were analyzed using the method of Umezaki and Iwamoto (1971), in first-filtered samples (0.45 μm) with added 10 mL 2M H 2 SO 4 , which were heated to 75–80 °C in a water bath for 2–3 h and cooled down; then the solution was diluted with distilled water to a volume of 50 mL. The concentrations of Hg-NR were determined in second-filter samples (0.45 μm) digested in a 1:1 HNO 3 + H 2 SO 4 mixture, from absorbance difference between Hg-susp and Hg-R after the flame atomic absorption spectroscopy (FAAS) assay. According to the specifications, the relative measurement error for Hg concentrations within the range of the analyzed samples was ≤20% (p = 0.95) at a quantitation limit of 0.01 μg g –1 . All samples were run in triplicate. Determination of inorganic compounds of Hg (II), Hg-OM and mercury sulfide (HgХ 2 , where X is Cl – , SO 4 2– etc., and HgS) in bottom sediments was carried out by a direct hybrid method combining thermal analysis with atomic absorption detection RA-915M (Shuvaeva et al., 2008). This technique allows you to determine some forms of mercury: stable (HgS и HgSe), labile (HgR 2 , were R is Cl, Br, O, SO 4 and thing lake that), toxic (methylmercury) and associated with organic matter (Hg-OM), for example, complex compounds with humic and fulvic acids. 3. Results 3.1. Lake and pore water chemistry The water of Lake Bolshoye Yarovoye belongs to the chloride class of sodium group, type III (Cl – ≥ Na + ), by redox conditions — to the oxidized type (Eh = +148...+26 mV), by alkaline-acid conditions — to the weakly alkaline class (pH = 8–8.2), by the value of total mineralization (138–150 g L –1 ) — to the family of brines (Table 1). Temperature stratification is observed in Lake Bolshoye Yarovoye with preservation of negative temperatures in summer. In August, the temperature of the surface layer of brine reached 21.6 °C, and at a depth of 4 m it was 18.5 °C. The water temperature at a depth of 8–9 m can be negative and range from –2 to –5 °C (Solovyanova et al., 2022). The pH and Eh values change with depth in the lake waters (Table 1). Table 1. Hydrochemical parameters of surface and pore waters of Lake Bolshoye Yarovoye Water and core depth, cm pH Eh mV DIC mg L –1 DOC mg L –1 SO 4 2– g L –1 Cl – g L –1 Fe tot mg L –1 Mn tot mg L –1 PO 4 3– mg L –1 TDS mg L –1 Epilimnion, 50 8.21 +148 89.9 40.9 5.80 79.30 0.001 0.090 1.98 138 Metalimnion, 400 8.17 +136 94.1 36.9 5.68 87.26 0.005 0.096 1.99 147 Hypolimnion, 820 8.04 +26 96 39.7 6.04 89.68 0.008 0.092 2.12 150 Water—sediment interface 7.22 –348 187.3 63.0 5.89 94.22 0.131 1.209 18.45 155 Unconsolidated sediment 7.10 –384 235.6 44.5 5.74 98.76 0.124 1.392 17.28 161 0–8 7.05 –329 75 79.3 9.78 89.60 0.051 2.343 0.91 162 20–28 6.90 –310 — — 10.16 92.09 0.045 2.093 1.03 165 32–40 6.91 –356 65.8 51.1 10.54 94.58 0.039 2.026 0.93 167 50–58 6.87 –322 — — 14.37 101.29 0.011 0.323 1.51 190 72–88 6.84 –288 68 65.4 16.02 100.46 0.008 0.344 0.73 186 88–104 6.85 –327 77.4 63.6 15.06 100.58 0.006 0.562 0.84 185 112–120 7 . 01 –367 75.1 47.3 10.58 97.80 0.021 1.338 2.45 181 140–148 6.48 –256 — — 12.35 99.42 0.016 0.479 1.94 179 170–176 6.36 –308 77.4 52.2 14.12 101.04 0.011 0.307 1.44 185 192–200 6.53 –360 61.9 77.3 19.04 109.4 0.016 0.201 2.80 206 231–238 6.38 –349 4.8 143.2 19.52 130.92 0.060 0.258 5.12 236 263–269 6.44 –358 5.3 141.2 18.08 133.76 0.064 0.358 3.57 236 306–310 6.47 –360 4.6 137.3 21.16 133.76 0.037 0.301 4.50 242 DOC — dissolved organic carbon, DIC — dissolved inorganic carbon. Fe tot — total dissolved iron, Mn tot — total dissolved manganese. TDS — total dissolved solids. Dash — no data. A stratification of the chemical characteristics of water is also observed in the lake: from the surface to the bottom, there is an increase in DIC concentration, dissolved Fe, anions (SO 4 2– , Cl – , PO 4 3– ), and mineralization. A decrease in DOC in the depth of the water column is noted from 40.9 to 39.7 mg L –1 . Mercury concentrations throughout the water column were below the detection limit. A significant increase in DIC, PO 4 3– , and dissolved Fe concentrations is observed at the water-sediment interface and in the unconsolidated sediment. The pH values decrease from 7.22 to 6.36 along the depth of bottom sediments (Table 1). The values of Eh vary from –384 to –230 mV, indicating strongly reducing conditions throughout the core. The pore waters show an increase in DOC, SO 4 2– , and Cl – with depth. The pore waters of the first meter of sediment are characterized by a decrease in the content of dissolved Fe. A significant increase in dissolved Mn content from 0.09 to 2.4 mg L –1 is observed within the upper 40 cm of the sediment. For the lower part of bottom sediments (230–310 cm), there is a significant decrease in DIC from 62 to 5 mg/L and a strong increase in DOC (up to 143 mg L –1 ). 3.2. Stratigraphy and mineral composition of bottom sediments The structure of bottom sediments of Lake Bolshoye Yarovoye is shown in Fig. 2a. The age of the bottom sediments is estimated at 7600±60 cal. years BP. According to our data, the calibrated age of the bottom sediments at a depth of 58–60 cm is 2660±30 cal. years BP, which corresponds to the pre-industrial era. The bottom sediments are marly clays with relatively high content of terrigenous component (up to 85%) and carbonates (up to 22%). Iron concentrations along the core vary from 2.53 to 4.16% and average 3.63%. Manganese concentrations along the core vary from 356 to 614 ppm and average 480 ppm. Two types of bottom sediments can be distinguished: these are dark and watered hydrogen sulfide silt (density = 1.09 g/cm 3 , moisture content = 29.02%) located at the depth of 0–182 cm, below this are lighter and denser lake sediments (density = 1.39 g/cm 3 , moisture = 21.77%). The modern lake deposits (0–51 cm) consist of black mineralized sulfide muds (peloids). This interval is characterized by an increase in total Fe contents. Below (51–72 cm) there are dark gray sulfide silts, which are characterized by a decrease in Fe. The interval from 72 to 104 cm has distinct boundaries and stands out visually. It is represented by gray silts, which mark the change in the conditions of lake sedimentogenesis. This is reflected in the chemical composition of the bottom sediments. The upper boundary of this interval has an increase in the terrigenous component and a decrease in carbonates. The lower boundary of this interval has a decrease in the terrigenous component and an increase in carbonates and Fe. The interval of 104–182 cm are hydrogen sulfide silts similar to bottom sediments from the interval of 51–72 cm. Further on there are sediments of another type, which are represented by gray-bluish dense clays. These sediments contain thin layers (0.2–1 cm) of whitish, sometimes dark gray or dark green color. For this interval of bottom sediments, there is a trend of decreasing total iron content with depth. According to XRD analysis, among the terrigenous minerals in the bottom deposits, quartz, illite, mica, and plagioclase dominate. In subordinate quantities, chlorite and smectite are present, while even fewer amounts of K-feldspars (potassium feldspars) and kaolinite are found. Amphibole is contained in trace amounts. Authigenic minerals identified include calcite, gypsum, and halite. At a depth of 302–310 cm there are thin (up to 0.5 cm) and light layers with a large number of small crystals of gypsum and halite. Pyrite was detected in trace amounts in the 104–112 cm interval. SEM data show the presence of pyrite framboids in the unconsolidated sediment (Fig. 2b). The Fe-Ti-Mn intermetallic (FeO = 45.14%, TiO 2 = 51.69%, MnO = 2.25%) were detected in the upper 5 cm of the sediment (Fig. 2c). They are apparently of a technogenic nature. Iron sulfides, represented mainly by pyrite, were found in the upper 5 cm of the sediment. 3.3. Distribution of C, H, N, S in plankton and bottom sediments The content of total organic carbon (TOC) by bottom sediments depth varies from 1.12 to 2.23% (Fig. 3). The highest TOC contents (5.23%) were found in unconsolidated sediment and in zooplankton (Table 2). The distribution of hydrogen throughout the core is generally consistent and does not exceed 1%, except for unconsolidated sediment and the interval 109–113 cm, where H values are 1.26% and 1.04%, respectively. Low nitrogen contents are characteristic of Lake Bolshoye Yarovoye throughout the core, being below the detection limit of the method, which is associated with the material composition of the bottom sediments (clays). Significant N contents were detected only in unconsolidated sediment and zooplankton, which amounted to 0.59 and 6.63%, respectively. The distribution of sulfur is not homogeneous throughout the depth of the core (Fig. 3). In the upper interval (0–51 cm), S distribution is relatively consistent, ranging from 0.89 to 1.04%. Sulfur contents increase to 1.70–3.28% in the 51–130 cm. In the middle interval of 146–181 cm, sulfur concentrations decrease to 1.20–1.99%. In the lower interval (200–310 cm), S contents increase to 2.51–2.86%. The uneven distribution of sulfur against consistent TOC and H values likely reflects changes in intra-lake conditions throughout the Holocene period, such as fluctuations (increase/decrease) in lake salinity. An increase in reduced forms of sulfur (S (II)) is observed with depth (Fig. 3, Table 2). Table 2. Chemical composition of zooplankton, unconsolidated sediment (u.s.), and upper 5 cm of bottom sediments of Lake Bolshoe Yarovoye C, % H, % N, % S, % S (II), % Hg total , ppm Hg-OM, ppm HgS+HgSe, ppm Fe, % Mn, ppm A. salina 37.49 5.81 6.63 1.00 — 0.28 0.28 <0.01 0.058 185 U.s. 6.19 1.26 0.59 1.04 0.1 1.7 1.1 0.6 3.689 614 0–5 cm 2.27 0.84 <0.01 0.98 0.23 0.8 0.5 0.3 3.959 539 <0.01 — below the detection limit. Dash — no data. 3.4. Reactive and non-reactive mercury in lake and pore water The concentration of the Hg-dc (dissolved + colloidal) fraction in lake water is below the detection limit (<0.02 ppm) (Table 3). Mercury in dissolved form is found only in unconsolidated sediment (0.07 ppm) and at the water—sediment interface (0.15 ppm). At the water—sediment interface, a predominance of non-reactive mercury specie (70%) over reactive Hg (30%) was found. There is a clear predominance of mercury in the suspended (Hg-susp) fraction over the Hg-dc fraction (almost 2-fold). The unconsolidated contains the highest amount of mercury in the Hg-dc fraction (0.17 ppm), of which more than 82% is in reactive specie. The concentration of suspended mercury fraction in the epilimnion (0.5 m) is below the detection limit. The presence of Hg-susp is found in the metalimnion (4.0) and hypolimnion (8.2 m) of the lake. With depth, an increase in suspended mercury 0.37 to 0.59 ppm is noted. In the metalimnion, more than 67% of mercury is in non-reactive specie (Hg-NR), while in the hypolimnion, Hg-NR accounts for only 44%, with the remaining 56% being reactive specie (Hg-R). At the water—sediment interface, the mercury content is 0.11 ppm, of which all Hg is in non-reactive specie. No suspended mercury fraction was detected in the unconsolidated sediment and the underlying interval. Significant Hg-susp values of 37 ppm were found only in deep intervals of bottom sediments (Table 3). Table 3. The fractions of mercury in surface and pore waters of Lake Bolshoye Yarovoye: dissolved + colloidal (Hg-dc) and suspended (Hg-susp) Water and core depth, cm Hg-dc, µg L –1 Hg-susp, µg L –1 Hg total Hg-R Hg-NR Hg total Hg-R Hg-NR Epilimnion, 50 — — — — — — Metalimnion, 400 — — — 0. 37 0.25 0.12 Hypolimnion, 820 — — — 0.59 0.26 0.33 Water—sediment interface 0.07 0.03 0.04 0.11 0.11 — Unconsolidated sediment 0.17 0.03 0.14 — — — 112–120 — — — — — — 300–310 — — — 0. 37 0.25 0.12 Hg total — total mercury, Hg-R — reactive mercury (non-organic), Hg-NR — non-reactive mercury (organic). Dash — no data. 3.5. Distribution and species of mercury in plankton and bottom sediments The mercury content in plankton is 0.28 ppm (Table 2) and in sediment varies from 0.01 to 4.5 ppm, averaging 2.3 ppm (Fig. 3). In unconsolidated sediment, the total mercury concentrations are 1.7 ppm. The distribution of mercury throughout the core is non-uniform, with three peaks identified: the first at a depth of 8–11 cm (1.5–2.3 ppm), the second in the interval of 26–28 cm (0.9 ppm), and the third at a depth of 117–119 cm (4.5 ppm). In the 120–300 cm interval, mercury content decreases to 0.011–0.8 ppm. At a depth of 300–310 cm, mercury concentrations are below the detection limit. The upper part (0–120 cm) of the bottom sediments is of particular interest as it accumulates Hg and undergoes changes in mercury species (Fig. 3). Previously, the presence of anthropogenic mercury in the unconsolidated sediment of the lake was established. However, through the investigation of a long drilling core, the migration of Hg downwards through the profile of bottom sediments has been identified, reaching a depth of 120 cm (Fig. 3). In the interval of 117–119 cm, there is an accumulation of mercury with an increase in its concentration by two orders of magnitude (from 0.04 to 4.5 ppm). Various forms of mercury occurrence have been identified in plankton (Table 2) and bottom sediments (Fig. 3). Plankton only demonstrates a concentration of Hg-OM at 0.28 ppm. Unconsolidated sediment exhibits the highest levels of Hg-OM at 1.1 ppm, accompanied by low concentrations of HgS+HgSe at 0.6 ppm. Within the upper section of bottom sediments (0–4 cm), Hg-OM predominates, constituting up to 65%, compared to HgS+HgSe at 40%. Moving deeper into the sediment profile, there is an equitable distribution between Hg-OM (50%) and HgS+HgSe (50%). In the interval of 19–51 cm, the proportion of Hg-OM increases to 52–60%, subsequently decreasing to 30–45% within the interval of 98–113 cm. At a depth of 118–120 cm, there is an increase in Hg-OM specie to 62%, accompanied by a decrease in HgS+HgSe. Notably, oxidized mercury species (HgR 2 ) appear at 14% concentration within this interval. Apparently, HgR 2 is present throughout the section (especially in the upper intervals), but its concentrations are below the detection limit of the method (Shuvaeva et al., 2008). However, a local increase in total mercury within the 117–118 cm interval enables the detection of all its forms, including HgR 2 . 4. Discussion 4.1. Water mercury chemistry Mercury is a typical complexing agent and migrates in the form of complex compounds with ligands such as Cl – , Br – , I – , HS – , S 2– . Due to its strong affinity for Hg, chloride ion is a potentially important factor influencing the adsorption of mercury in salt lakes. According to physicochemical modeling data, inorganic forms of mercury in the brine of Lake Bolshoye Yarovoye are represented by chloride complexes: HgCl 4 2– = 92–96%, HgCl 3 – = 2.7–5.9%, HgCl 2 0 = 0.25–2.5% (Table 4). These complexes determine increased availability of Hg for biological objects, in particular for the halophilic crustacean A. salina (Leonova et al. 2007) . Artemia concentrates up to 0.28 ppm of mercury in its composition (Table 2). According to Egorkina and Bender (2012) zooplankton inhabits nearly the entire water column (up to a depth of 7 m) of the lake, thus it can accumulate dissolved mercury from different depths. The ions of Hg are characterized by complexation with low molecular weight organic compounds and thiols (Beckers and Rinklebe 2017), which readily form complexes with mercury. These include both Hg 2+ and MeHg + . Low molecular weight thiols (such as mercaptoacetic acid, mercaptopropionic acid, cysteine, and glutathione) are formed under both oxidative and reductive conditions in hypolimnetic waters (Skyllberg 2012). The amount of DOC (Table 1), TOC, and S (Fig. 3) is sufficient to form low molecular weight thiols. Therefore, it would be erroneous to limit the presence of mercury only in chloride complexes. Our data on lake and pore water have been plotted on diagrams of prevailing mercury forms (Fig. 4). Mercury in inorganic complexes is present in the form of HgCl 4 2– (Fig. 4a) and as Hg(SR) 2 (Fig. 4b), which was not previously considered in the thermodynamic modeling of the forms of mercury in the aqueous phase (Leonova et al. 2007). It is important to note that thiol groups are associated with dissolved organic matter (DOM), therefore under these conditions (Fig. 4c), mercury will be present more likely as MeHgSR-DOM than MeHgCl. It is important to emphasize that our data are in excellent agreement with the findings of Skyllberg (2012). Another source of mercury input into the lake ecosystem is suspended particulate matter. This is confirmed by the presence of suspended forms of mercury (Hg-susp) in the brine and the increase in Hg-susp with depth in the water column (Table 3). Mercury can enter the lake in suspension, adsorbed on clay minerals or OM; these could be technogenic formations, for example, the detected Fe-Ti-Mn intermetallics (Fig. 2c). This is because the deposition of solid particles is considered the main mechanism for delivering mercury to the water—sediment interface, the main site of methylation. Diffusion (driven by redox potential) upwards from the sediment pore water is likely less significant (Ullrich et al. 2001). Plankton and suspended particulate matter enter bottom sediments. Decomposition of planktonic organic matter and breakdown of mercury-containing clay minerals lead to the leaching of Hg into the pore water (Table 3), where it can sorb onto iron sulfides according to (Skyllberg et al. 2021). Further destruction of sulfides during diagenesis may result in mercury entering the pore water and accumulating Hg lower in the core at the sediment type transition zone (117–119 cm). The active mineralization of planktonic organic matter in the 0–11 cm layer is confirmed by a decrease in sediment pH and Eh, an increase in pore waters PO 4 3– , DOC, and DIC, leading to the accumulation of dissolved Mn and Fe. The decrease in sulfate ions (SO 4 2– ) and increase in dissolved iron forms in this interval, followed by their decrease down the core, indicate the processes of bacterial sulfate reduction and pyritization. These processes can contribute to the accumulation of mercury in sediment, which indirectly confirms the local increase in total Hg in the intervals of 10–12 cm and 26–28 cm. The increase of chloride in pore waters along the depth of the core (Table 1) may also favor the concentration of mercury in the bottom sediments. Thus, the accumulation of mercury in pore waters and at the water—sediment interface indicates the mobility of Hg and its danger for the lake ecosystem. 4.2. Sediment mercury chemistry The accumulation of mercury in bottom sediments is typically attributed to the presence of clay minerals and organic matter (Beckers and Rinklebe 2017). The primary natural source of Hg in the sediments of Lake Bolshoye Yarovoye is predominantly aluminosilicate minerals (Malikova and Strakhovenko 2017), represented by quartz, illite, muscovite, and plagioclase. Clay minerals can also participate in mercury absorption, which is controlled by pH values. The pH influence both the surface charge characteristics of sediment particles and the dissolution/precipitation of metals (Beckers and Rinklebe 2017). Microbial decomposition of OM leads to a decrease in pH down the core from alkaline (pH 8.2) to slightly acidic (pH 6.4) values (Table 1). Changes in pH values can affect the concentration of mercury at local sediment sites, such as in the interval of 8–27 cm (Fig. 3). The presence of organic or inorganic complexing agents also influences the geochemistry of mercury. The formation of soluble humic complexes can significantly increase the solubility and mobility of Hg in aquatic systems, especially at pH > 5 (Ullrich et al. 2001). Another important factor contributing to the concentration of mercury in bottom sediments is its complexation involving dissolved organic matter (Beckers and Rinklebe 2017). However, dissolved organic matter (DOC) appears to play an insignificant role in mercury concentration, as there is no correlation between the increase in DOC in pore waters and the increase in Hg in the bottom sediments. For example, where the interval of 231–310 cm has the highest concentrations of DOC (137–143 mg L –1 ), yet the mercury content in both the bottom sediments (Fig. 3) and pore waters (Table 3) is below the detection limit. The accumulation of mercury, both within bottom sediments and pore water, appears to be driven by the precipitation/dissolution dynamics of iron and manganese oxides and oxyhydroxides according to (Tisserand et al. 2022). In a study conducted by Malikova and Strakhovenko (2017), a positive correlation between Hg and Mn in the sediment of Lake Bolshoye Yarovoye was established. The notable surge in dissolved forms of Fe and particularly Mn observed in the upper sediment intervals (0–40 cm) may indirectly signify processes involving the dissolution of iron and manganese oxides and oxyhydroxides under highly reducing conditions (Table 1). This phenomenon could potentially elevate the concentrations of dissolved mercury within the unconsolidated sediment and at the water—sediment interface (Table 3). It is noteworthy that a correlation exists between the distribution patterns of sulfur forms, TOC, sediment grain size composition, and mercury content (including its chemical forms) within lake sediments, as highlighted by Ullrich et al. (2001) and Wang et al. (2022). The sulfur cycle within bottom sediments may be intricately linked to the formation of methylmercury (MeHg), as suggested by Wang et al. (2022). The mobility of Hg (II) is governed by the formation of soluble polysulfides or organic complexes, as proposed by Ullrich et al. (2001). According to our findings, a correlation exists between the distribution of Hg-OM and S (II) down to a depth of 51 cm; however, this correlation is not discernible beyond this depth (Fig. 3). This association is likely attributed to the activity of microorganisms, which have the capacity to influence mercury geochemistry (Manceau et al. 2015). Various physiological groups of microorganisms inhabit the water and sediments of Lake Bolshoe Yarovoe, including heterotrophic, halophilic, and non-spore-forming bacteria (Solovyanova et al. 2022). Studies have demonstrated the presence of sulfate reducers belonging to the Desulfobacterota taxon, as well as halophilic sulfidogenic bacteria from the genera Halanaerobium and Halomonas, capable of iron reduction under anaerobic conditions, in the sediments of the nearby saline Lake Maloe Yarovoe, situated 32 km to the northwest (Maltsev et al. 2023). Certain groups of sulfate-reducing and iron-reducing bacteria possess the ability to methylate mercury, converting dissolved inorganic mercury into MeHg, while also participating in the sulfur biogeochemical cycle within sediments, facilitating the mutual transformation of various forms of sulfur (Ullrich et al. 2001). Consequently, bacterial sulfate reduction occurring within the upper sediment intervals may lead to mercury accumulation. Active processes of bacterial sulfate reduction are indirectly corroborated by: i. the reduction in sulfate ion concentrations and dissolved iron (refer to Table 1); ii. an increase in total iron (see Fig. 2a) and S (II) (refer to Fig. 3) within the bottom sediments; iii. the presence of iron sulfides (see Fig. 2b). The geochemistry of mercury within bottom sediments, encompassing both organic and inorganic forms, is subject to the influence of various sulfur compounds, including sulfate, sulfide, polysulfide, elemental sulfur (S 0 ), and pyrite (FeS 2 ), as elucidated by Skyllberg et al. (2021). Among these compounds, sulfide and polysulfide serve as potent ligands for Hg 2+ , thereby potentially restricting the biological availability of mercury and impacting the formation of methylmercury (MeHg). Consequently, the biogeochemical sulfur cycle within sedimentary deposits may exert a significant influence on MeHg formation (Wang et al. 2022). The formation of iron sulfides in the upper sediment intervals (Fig. 2b) may also contribute to the accumulation of mercury (Fig. 3). 4.3. The ecological condition of the ecosystem of Lake Bolshoye Yarovoye (comparison with regional and global background) The mercury enrichment of mesoplankton in Lake Bolshoye Yarovoye, in the immediate vicinity of the “Altaikhimprom” chemical plant, increases several times (1.1–2.3 ppm) compared to that in the background point on the opposite shore (0.46–0.84 ppm), indicating the technogenic nature of high mercury concentrations in A. salina . Plankton samples collected in August 2022 from the central part of the lake also showed lower Hg concentrations (0.28 ppm), which are comparable to mercury contents for A. salina from salt lakes in the south of Western Siberia, particularly the Altai region (Table 5). In contrast, zooplankton from salt lakes in the European part of Russia contains an order of magnitude less Hg: from 0.029 to 0.096 ppm. Thus, the enrichment of zooplankton with mercury is determined not only by the geochemical specificity of the mineralized brine of Lake Bolshoye Yarovoye, as evidenced by the chemical forms of mercury (Table 4), but also by anthropogenic factors. Table 4. Percentages (%) of Hg and Fe species in brine of Lake Bolshoye Yarovoye (Leonova et al. 2007) Element species % Hg HgCl 2 0 0.5 HgCl 3 – 2.7 HgCl 4 2– 96.8 Fe Fe(OH) 2 + 43.65 Fe(OH) 3 0 55.41 Fe(OH) 4 – 0.94 Since mercury in the soils of the lake’s watershed averages 0.04 ppb (Malikova and Strakhovenko 2017), which is significantly below the maximum permissible concentrations set in Russia (2.1 ppb) (МРС, 2006), the main source of Hg is “Altaikhimprom” chemical plant. This was confirmed by our studies (Leonova et al. 2007). Further, mercury can infiltrate the lake environment where it is concentrated during filtration by mesozooplankton A. salina , eventually depositing into the bottom sediments. In our opinion, the main diffuse sources of technogenic mercury entering the lake are the coastal dumps of solid waste from the “Altaikhimprom”, especially during the snowmelt period, which is consistent with the data of other researchers (Temerev et al. 2002). However, the concentration of Hg in the water of Lake Bolshoye Yarovoye is lower than in regional salt lakes, as well as salt lakes in the European part of Russia and America (Table 5). This indicates that the input of “technogenic” mercury into lake mainly occurs in suspended form (Table 3). This does not lead to the accumulation of mercury in the lake water. Mercury is concentrated in plankton (especially in the vicinity of the plant) and bottom sediments, for which Hg contents (up to 4.5 ppm) are higher than in other saline water bodies with higher mercury contents (Table 5). This could pose an ecological risk to the ecosystem of Lake Bolshoye Yarovoye. Table 5. Mercury content in water, Artemia and bottom sediments of salt lakes in Russia and the world Lake / region Salinity, g L –1 Hg in water µg L –1 Hg in artemia, ppm Hg in sediments, ppm Reference Russia, south of Western Siberia Bolshoye Yarovoe, Altai region 138–150 <0.0 1– 0.0 4* 0.28 0.01–4.5 Our data (2022) Kulundinskoe, Altai region 94 0.06 0.29 0.01 Leonova et al. 2007 Maloye Yarovoe, Altai region 262 0.08 0.12 0.01 Bolshoy Bagan, Novosibirsk region 282 <0.01 — 0.0013–0.022 Our data (2019) European Russia Kiyatskoe, Crimea 83 0.020–0.363 — 0.017 Mirzoyeva et al. 2015 Kirleutskoye, Crimea 190 0.019 0.029–0.096 — Evstafeva et al. 2021; Shadrin et al. 2022 Aktashskoe, Crimea 214 0.022 0.038 0.011–0.026 Stetsyuk et al. 2018; Shadrin et al. 2022 World objects The Great Salt Lake, Utah, USA 150 0.005 — 0.5–1.5 Wurtsbaugh et al. 2020; Wright et al. 2020 Devils, North Dakota, USA 11–25 0.04–0.15 — 0.005–0.15 Swenson and Colby 1954; Lent and Alexander 1997 Dash — no data, <0.01 — less than detection limit, * — according to Leonova et al. 2007. 5. Conclusions i. Mercury primarily exists in inorganic complexes in the form of HgCl 4 2– and Hg(SR) 2 . In both lake and pore waters, mercury is predominantly found in the form of MeHgSR-DOM rather than MeHgCl. ii. Dissolved organic matter exhibit negligible influence on mercury concentration within the sediment of Lake Bolshoye Yarovoye. Instead, the accumulation of mercury in bottom sediments is attributed to the precipitation/dissolution processes oxides and oxyhydroxides of Fe and Mn. iii. The geochemistry of mercury within bottom sediments, encompassing both organic and inorganic forms, is subject to the influence of various sulfur compounds, including sulfate, sulfide, polysulfide, elemental sulfur, and pyrite. Sulfide and polysulfide serve as potent ligands for Hg 2+ , thereby potentially restricting the biological availability of mercury and impacting the formation of methylmercury. iv. Within the upper 50 cm of sediment, a correlation exists between the distribution of Hg-OM and S (II). This correlation is linked to the activity of sulfate-reducing microorganisms. v. The vertical migration of technogenic mercury in the sediment core due to its high water content has been identified. At a depth of 110–120 cm, a geochemical barrier emerges, characterized as a zone of active transformation of mercury forms. A geochemical barrier is formed by a combination of processes such as sorption on clay minerals and organic matter, as well as alterations in sediment density. vi. By employing a set of geochemical criteria, it has been deduced that there exists moderate mercury contamination within the bottom sediments and mesoplankton of Lake Bolshoye Yarovoye within the influence zone of the “Altaikhimprom” plant. The primary source of diffuse technogenic mercury influx into the lake stems from the coastal solid waste dumps of the plant, particularly during the snowmelt period. Declarations CRediT authorship contribution statement Maria Gustaytis : Conceptualization, Writing—original draft preparation, Methodology, Investigation. Anton Maltsev: Conceptualization, Editing, Investigation, Fieldwork. Galina Leonova: Methodology, Supervision. Sergey Krivonogov: Funding, Fieldwork. The first draft of the manuscript was written by Mariya Gustaytis and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Declaration of competing interest The authors declare no conflict of interest. Data availability Data will be made available on request. Funding The analytical studies were carried out in the Analytical Center for multi-elemental and isotope research SB RAS. Work is done on state assignment of V.S. Sobolev Institute of Geology and Mineralogy Siberian Branch Russian Academy of Sciences, Projects No 122041400193-7 and No 122041400252-1. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6909634","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":501914523,"identity":"d6cf0d84-4f63-47a5-b847-e0a6dec9d19c","order_by":0,"name":"Mariya Gustaytis","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA50lEQVRIiWNgGAWjYNACAwYeBvbGBqLVMzYwGBjwMPAcJEkL0BoGiQQi1ctHpD9/8KPgj4z8zMfNr24w3LHnb+B9JoFPi+GNHMPGHqDDDG4ntlnnMDxLnHGA3Qy/lhk5jA08IC3SiW3GOQyHEwwY2NgIaEl/2PgHqEV+5kGwFnuCWuQlEgybQbYw3GBsfgzUwriBkBYDnjeGs2UMjHkMziS2MecYHE6ccZiN2QKvLe3pDz6++SNnL99+/PHnnIrD9vztbYw38NpyAMEGugcYPwzM+NSDbGlAsJk/EFA8CkbBKBgFIxQAAJ9cQ02VSD7xAAAAAElFTkSuQmCC","orcid":"","institution":"Sobolev Institute of Geology and Mineralogy SB RAS","correspondingAuthor":true,"prefix":"","firstName":"Mariya","middleName":"","lastName":"Gustaytis","suffix":""},{"id":501914527,"identity":"828c489b-4cce-4698-8b0b-eae921ee1859","order_by":1,"name":"Anton Maltsev","email":"","orcid":"","institution":"Sobolev Institute of Geology and Mineralogy SB RAS","correspondingAuthor":false,"prefix":"","firstName":"Anton","middleName":"","lastName":"Maltsev","suffix":""},{"id":501914529,"identity":"ada85d87-70ed-4341-99f4-43596e3cb461","order_by":2,"name":"Galina Leonova","email":"","orcid":"","institution":"Sobolev Institute of Geology and Mineralogy SB RAS","correspondingAuthor":false,"prefix":"","firstName":"Galina","middleName":"","lastName":"Leonova","suffix":""},{"id":501914530,"identity":"16b648d6-49fe-4f32-b63e-753b53abb965","order_by":3,"name":"Sergei Krivonogov","email":"","orcid":"","institution":"Sobolev Institute of Geology and Mineralogy SB RAS","correspondingAuthor":false,"prefix":"","firstName":"Sergei","middleName":"","lastName":"Krivonogov","suffix":""}],"badges":[],"createdAt":"2025-06-17 02:53:19","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6909634/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6909634/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12665-025-12735-x","type":"published","date":"2025-12-24T15:57:18+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":89384222,"identity":"6abe6c77-a8b8-48ac-80c9-9b943a9366a3","added_by":"auto","created_at":"2025-08-19 12:24:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1265639,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of Lake Bolshoye Yarovoe (a, b) and point of brine, plankton, and core sampling (c).\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6909634/v1/ebec5abbf8c05ef3d2dbe677.png"},{"id":89384225,"identity":"9454442b-f605-4aed-829e-94feba7c134b","added_by":"auto","created_at":"2025-08-19 12:24:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":1081175,"visible":true,"origin":"","legend":"\u003cp\u003eA) Core section structure, component composition of bottom sediments, Fe, and Mn distribution: 1. Black, highly watered hydrogen sulfide silts (0–51 cm); 2. Dark gray hydrogen sulfide silts (51–72 cm); 3. Gray silts (72–104 cm); 4. Gray-blue, dense clays (104–310 cm). B) Framboidal pyrite in unconsolidated sediment. C) Fe-Ti intermetallic compounds with an admixture of Mn in the 3–5 cm sediment layer. SEM photos and energy dispersive spectra captured using \u003cem\u003eTescan Mira 3 LMU\u003c/em\u003e. *Dates by (Kosareva et al. 2020).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6909634/v1/99567c4526b7005ad9743299.png"},{"id":89388094,"identity":"98cef3d5-90aa-4399-af7f-d26fd8b2b98f","added_by":"auto","created_at":"2025-08-19 12:40:17","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":322978,"visible":true,"origin":"","legend":"\u003cp\u003eThe distribution of mercury species, sulfur species, total organic carbon (TOC), and hydrogen (H) in bottom sediments of Lake Bolshoye Yarovoye.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6909634/v1/2d17a1392d9e60d270c58a52.png"},{"id":89385805,"identity":"d15872da-742a-4f33-b4a2-8ccf74d16571","added_by":"auto","created_at":"2025-08-19 12:32:17","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":115272,"visible":true,"origin":"","legend":"\u003cp\u003eDiagram illustrating the predominant forms of mercury in lake and pore water under oxygenated conditions in the absence (A, B) and presence (C) of low molecular weight thiols. 1. Data from Skyllberg (2012); Our data: 2. lake water, 3. pore water.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6909634/v1/4ab42e9b13e8c7334d0d1c79.png"},{"id":99172481,"identity":"c680b2b8-9108-4b54-ae8a-2f8fcbc68254","added_by":"auto","created_at":"2025-12-29 16:10:17","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3822417,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6909634/v1/7dd9bd94-72ae-4e7c-848c-41e95fbf20e3.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Mercury species in zooplankton, brine, and bottom sediments of hyperhaline Lake Bolshoye Yarovoye (south of Western Siberia)","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eMercury is a highly toxic element and has the ability to bioaccumulate. Mercury has the highest ionization potential and a wide variety of chemical forms Hg in the environment. The potential risk and bioavailability of mercury for aquatic organisms directly depends on its chemical forms in aqueous solution and bottom sediments (Mason et al. 1993; Hai Luu Duc et al. 2010). Compounds of mercury with low-molecular-weight organic ligands, such as methylmercury, or free hydrated ions, exhibit a cumulative effect and higher stability in the aquatic environment. These forms of mercury are more toxic than inorganic forms of Hg. The methylated form of mercury has the most negative impact on aquatic biota (UNEP 2019). In water bodies, mercury accumulates in the surface layers of bottom sediments and can be included in various links of trophic chains (Zhu et al. 2018; Branfireun et al. 2020). Chemical compounds of mercury can accumulate both in aquatic organisms and in bottom sediments. In bottom sediments, mercury is transformed from an inorganic form to a methylated form (Fleck et al. 2016; D\u0026oacute;rea et al. 2023). Judgments about the toxicity of mercury are based on its forms in bottom sediments rather than on the total concentration. Bottom sediments are used as indicators of water ecosystem pollution.\u003c/p\u003e\n\u003cp\u003eDue to the high toxicity of mercury compounds to living organisms there is a greater relevance for comprehensive biogeochemical studies, allowing us to trace the migration paths of Hg in various components of the biosphere. These studies allow tracking the migration pathways of mercury in various components of the biosphere. The peculiarities of mercury migration and its bioaccumulation under natural and anthropogenic conditions in the south of Western Siberia are examined using the example of the impact of the chemical production facility of \u0026ldquo;Altaikhimprom\u0026rdquo;. Until 2014, the chemical plant was a major producer of chemical reagents in Russia, including two crystalline modifications of mercury oxides HgO (yellow and red), for the production of which metallic mercury was used as raw material. \u0026ldquo;Altaikhimprom\u0026rdquo; is located in the Altai region of Russia, near the town of Yarovoye, on the shore of the hyperhaline (salty) Lake Bolshoe Yarovoe.\u003c/p\u003e\n\u003cp\u003eSalt lakes are particularly susceptible to anthropogenic influence as they lack surface and groundwater outflows. High mineralization of water and reducing conditions at depth do not contribute to the precipitation of heavy metals, which leads to their accumulation in salt lakes (Wurtsbaugh et al. 2020). Most salt lakes are characterized by a specific halophilic biota, often represented by various branchiopods, which can also concentrate large amounts of heavy metals. As a result of the death of branchiopods and their microbiological processing in salt lakes, organic muds, or therapeutic sulfide muds (peloids), are formed. They can accumulate heavy metals that come from the biota.\u003c/p\u003e\n\u003cp\u003eThe hyperhaline Lake Bolshoye Yarovoye is a large balneological resort and physiotherapeutic mud baths (Egorkina and Bender 2012).\u0026nbsp;Our previous studies have demonstrated that the chemical plant \u0026ldquo;Altaikhimprom\u0026rdquo;, located on the shore of the lake, has created an unfavorable environmental situation in the near zone of its influence. According to our long-term research, the main diffuse sources of anthropogenic mercury input into the lake were the coastal dumps of solid mercury-containing waste from the plant,\u0026nbsp;especially during the snowmelt period, which is consistent with the findings of other researchers (Temerev et al.\u0026nbsp;2002).\u003c/p\u003e\n\u003cp\u003eA universal method that would allow the determination of all forms of mercury in brine (including organic form) has not yet been proposed due to the complexity of the composition of brine. Mercury compounds in environmental objects are determined using combined methods. They are multi-stage processes. These processes include the stage of preliminary extraction of the compounds being determined into a solution or gas phase. They are then separated by liquid (gas) chromatography or capillary electrophoresis followed by element-selective detection, usually by atomic spectrometric methods.\u0026nbsp;In the analysis of solid natural samples, a necessary step is the preliminary transfer of analytes into solution by extraction or sorption. At this stage, losses of the determined forms are often observed, as well as their transformation from one form to another (Shuvaeva et al. 2008). Currently, the most promising method should be recognized as a direct hybrid method for the determination of inorganic compounds of mercury (II), monomethylmercury and mercury sulfide in solid samples. The method combines thermal analysis with atomic absorption detection, based on the differences in evaporation temperatures for various mercury compounds (Shuvaeva et al. 2008; Gustaytis et al. 2021).\u003c/p\u003e\n\u003cp\u003eAt present, the vertical distribution of mercury forms in hyperhaline environments has not been studied well enough. Thus, the goal of the work is to identify the characteristics of the concentration and distribution of chemical forms of mercury in plankton, brine and along the vertical profile of bottom sediments of the hyperhaline Lake Bolshoye Yarovoye using the direct hybrid method for determining Hg compounds. The study based on several objectives:\u003c/p\u003e\n\u003cp\u003ei.\u0026nbsp;To establish the distribution of mercury in brine and plankton;\u003c/p\u003e\n\u003cp\u003eii.\u0026nbsp;To determine the forms of mercury in biota, water and sediments;\u003c/p\u003e\n\u003cp\u003eiii.\u0026nbsp;To establish the degree of pollution of the bottom sediments of Lake Bolshoe Yarovoe after the closure of the \u0026ldquo;Altaikhimprom\u0026rdquo; enterprise;\u003c/p\u003e\n\u003cp\u003eiv.\u0026nbsp;To identify the features of the concentration and distribution of mercury forms along the vertical profile of bottom sediments using the direct hybrid method for determining Hg compounds (such work has not been carried out in the region);\u003c/p\u003e\n\u003cp\u003ev. To determine the causes of the transformation of mercury forms in the brine\u0026mdash;plankton\u0026mdash;bottom sediments system.\u003c/p\u003e"},{"header":"2. Materials and methods","content":"\u003cp\u003e\u003cem\u003e2.1. Physiographic background and site description\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eLake Bolshoe Yarovoe occupies a deep depression (approximately 25 m) in the western part of the Kulunda Plain of the Ob-Irtysh interfluve (Altai Territory, southern West Siberia). The lake is located 6 km southwest of the town of Slavgorod (Fig. 1a, b).\u0026nbsp;The northern and northeastern shores of the lake are gentle, rising 1.5\u0026ndash;2.0\u0026nbsp;m above the water level\u0026nbsp;(Fig. 1c).\u0026nbsp;The southwestern shores of the lake are steep, reaching heights of up to 20 m. The lake is situated at an elevation of approximately 84 m above sea level.\u0026nbsp;The length of the lake is 11\u0026nbsp;km and the width is 7.9\u0026nbsp;km.\u0026nbsp;The water area of the lake is 70\u0026nbsp;km\u003csup\u003e2\u003c/sup\u003e, with an average depth of 4\u0026nbsp;m and a maximum depth of around 8\u0026nbsp;m (Rudaya et al. 2012). Lake Bolshoye Yarovoye is one of the deepest at the Kulunda Plain.\u003c/p\u003e\n\u003cp\u003eThe surrounding plain provides aeolian material input to the lake. The lake shoreline is not indented. Such relief characteristics result in the deposition of terrigenous material into the lake during spring runoff and precipitation events (Kosareva et al. 2020). The lake is not fed by rivers. Positive water balance is maintained through spring runoff from the watershed, groundwater seepage from steep shores, and winter and summer precipitation. Negative water balance is attributed to evaporation. Intense evaporation and low precipitation rates in the region led to a high degree of water salinity (Malikova et al. 2008).\u003c/p\u003e\n\u003cp\u003eThe high salinity of the water contributes to the development of specific biota in the lake, which is represented by halophilic species such as the branchiopod crustacean \u003cem\u003eArtemia salina\u003c/em\u003e L. Lake Bolshoye Yarovoye is one of the most promising lakes in the region for harvesting \u003cem\u003eA. salina\u003c/em\u003e. Industrial procurement of artemia has been carried out since 1978. Over the past 20 years, the volume of artemia procurement has increased from 14 to 483 tons. The \u0026ldquo;Altaikhimprom\u0026rdquo; chemical plant located on the northern shore of the lake and mercury-containing waste located in the northeastern part of the lake (Fig. 1c) is a source of accumulation of mercury in brine and in \u003cem\u003eA. salina\u003c/em\u003e.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.2.\u0026nbsp;Water and sediment sampling\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eSampling of zooplankton (\u003cem\u003eArtemia salina)\u003c/em\u003e, brine and well drilling were carried out at the end of August 2022 in the central part of the lake (coordinates: N 52.86923\u0026deg; and E 78.60915\u0026deg;) (Fig. 1c). The brine was sampled with a bathometer throughout the entire depth of the lake in the epilimnion (0.5), metalimnion (4.0) and hypolimnion (8.2 m). Unconsolidated sediment (bottom sediments that is loosely arranged and unstratified) was collected using a bathometer in the bottom water layer. \u003cem\u003eA. salina\u003c/em\u003e was sampled using the small plankton net. Plankton samples were weighed, then dried to an air-dry state and transported to the laboratory.\u003c/p\u003e\n\u003cp\u003eThe bottom sediments cores were collected in the central part of the lake (Fig. 1c). The coring operations were carried out from an inflated pontoon with a load of 5 tons using a \u003cem\u003eLivingston\u003c/em\u003e-type piston sampler driven by vibration technology (Krivonogov et al. 2012). The sampler enables sequential retrieving of undisturbed lots of the core that are 2 m in length and 7.5 cm in diameter. The total core length was 4.83\u0026nbsp;m. The core was divided into 2\u0026ndash;3 cm layers for geochemical studies.\u003c/p\u003e\n\u003cp\u003eThe cores obtained were measured for pH and Eh with the \u003cem\u003eAnion 4100\u003c/em\u003e ionometer (Infrapack-Analit, Russia), wrapped in plastic film, placed in tight plastic boxes, and transported to Novosibirsk for investigation. The lots were split in halves and documented. One half was used for pore water extraction and the other half was used for all other methods. Pore water was squeezed out of 10-cm pieces of the core into tight syringes, protected from oxygen supply according to the standard method (Jahnke\u003cdel cite=\"mailto:Мальцев%20Антон%20Евгеньевич\" datetime=\"2025-02-11T10:34\"\u003e,\u003c/del\u003e 1988) with the \u003cem\u003eOmec PI.88.00\u003c/em\u003e hydraulic press (Omec S.n.c., Mugio, Italy).\u003c/p\u003e\n\u003cp\u003eSamples of the lake water were collected at the coring place by a bathometer near surface and near bottom. Temperature, pH, and Eh were immediately measured in the samples with an \u003cem\u003eAnion 4100\u003c/em\u003e ionometer. Raw water samples were used for hydrochemical analysis, and for elemental analysis, the water was vacuum-filtered through 0.45 \u0026micro;m filters and packed in plastic bottles with the addition of concentrated nitric acid (1 ml L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) for preservation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.3.\u0026nbsp;Analytical methods\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eConcentrations of anions in the lake and pore water samples were determined by capillary zone electrophoresis (CZE) (Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e, PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e), on \u003cem\u003eAgilent\u0026nbsp;7100\u003c/em\u003e (Agilent Technologies, USA). Elements (Fe, Mn) in pore water and bottom sediments were measured by atomic emission spectroscopy with inductively coupled plasma (ICP-AES), on IRIS \u003cem\u003eAdvantage\u003c/em\u003e ICP-AES spectrometer (Thermo Jarrell Ash Corp., Franklin, MA, USA). Authigenic components (carbonates) were estimated by their successive removal with HCl, and the terrigenous mineral part was the residue.\u003c/p\u003e\n\u003cp\u003eTotal dissolved carbon (TDC) and proportions of dissolved inorganic and organic carbon (DIC and DOC, respectively) in water were determined on an AG \u003cem\u003eMulti N/C\u003c/em\u003e 2100S analyzer (Analytik Jena GmbH, Jena, Germany). TDC was estimated by the amount of CO\u003csub\u003e2\u003c/sub\u003e released from samples after catalytic oxidation at 950\u0026deg; in the presence of oxygen flux in a quartz reactor. DIC was estimated by the amount of CO\u003csub\u003e2\u003c/sub\u003e released from samples after digestion in 10% H\u003csub\u003e3\u003c/sub\u003ePO\u003csub\u003e4\u003c/sub\u003e. DOC was found as the difference between TDC and DIC.\u003c/p\u003e\n\u003cp\u003eTotal organic carbon (TOC) was determined by Tyurin\u0026rsquo;s method. The method is based on the oxidation of organic matter with chromic acid to form carbon dioxide (Vorobyova, 1998). Contents of H, N, and S were measured on an automatic CHNS analyzer \u003cem\u003eEuro EA 3000\u003c/em\u003e (EuroVector S.p.A., Milan, Italy) following Fadeeva et al. (2008).\u003c/p\u003e\n\u003cp\u003eThe speciation of sulfur in sediment samples, total sulfur (S\u003csub\u003etotal\u003c/sub\u003e), sulfate (S\u0026nbsp;(VI)), and sulfide (S\u0026nbsp;(II)), was studied with ICP-AES. S\u003csub\u003etotal\u003c/sub\u003e was determined by high-temperature digestion in HNO\u003csub\u003e3\u003c/sub\u003e under a lid and then by digestion in HCl, which transforms sulfide into sulfate. S (II) was removed from specimens via digestion in diluted HCl and subsequent filtering of the residue, whereby only sulfate sulfur remained. The amount of S (II) was estimated as the difference between S\u003csub\u003etotal\u003c/sub\u003e and S (VI).\u003c/p\u003e\n\u003cp\u003eMineral composition of the sediments was analyzed by the X-ray powder diffraction (XRD) method on a \u003cem\u003eDRON-4\u003c/em\u003e diffractometer (Cu-K\u0026alpha; radiation), at the Analytical Center for Multielement and Isotope Studies of the Institute of Geology and Mineralogy SB RAS. Morphology of mineral grains and their element composition were studied in selected samples by scanning electron microscopy (SEM) on a \u003cem\u003eTescan Mira 3 LMU\u003c/em\u003e microscope according to Goldstein et al. (1981).\u003c/p\u003e\n\u003cp\u003eThe sediments were \u003csup\u003e14\u003c/sup\u003eC dated by accelerator mass-spectrometry (AMS) method in the Center of Collective Use \u0026ldquo;Cenozoic geochronology\u0026rdquo; of SB RAS, Novosibirsk. The dates were calibrated and converted into calendar years using the CALIB 8.2 [WWW program] at http://calib.org.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e2.4. Chemical analyses of\u0026nbsp;\u003c/em\u003e\u003cem\u003emercury\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eLake and pore water samples were filtered through cellulose acetate membrane filters (GVS Filter Technology, USA) with a pore size of 0.45 \u0026micro;m (Howe and Clark 2002). Two fractions of mercury were obtained: dissolved + colloidal (Hg-dc) and suspended (Hg-susp). Each of the fractions was analyzed of mercury\u0026nbsp;species:\u0026nbsp;reactive mercury (Hg-R) and non-reactive mercury\u0026nbsp;(Hg-NR).\u003c/p\u003e\n\u003cp\u003eAccording to Lindqvist and Rodhe (1985), the reactive forms of mercury include Hg\u003csup\u003e2+\u003c/sup\u003e, HgX, HgX; and HgXi- with X = OH\u003csup\u003e\u0026ndash;\u003c/sup\u003e, Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e and Br\u003csup\u003e\u0026ndash;\u003c/sup\u003e; suspended HgO; complexes of Hg\u003csup\u003e2+\u003c/sup\u003e with organic acids; Non-reactive forms include CH, Hg\u003csup\u003e+\u003c/sup\u003e, CH, HgCl; CH, HgOH and other organomercury compounds, Hg(CN); HgS and Hg\u003csup\u003e2+\u003c/sup\u003e associated with sulfur in organic matter.\u003c/p\u003e\n\u003cp\u003eReactive/non-reactive (or inorganic/organic) mercury can be determined in various ways (Bloom et al. 2003; Umezaki and Iwamoto 1971), by successively leaching groups of compounds at each step, as in the sequential leaching procedures (Bloom et al. 2003). In the absence of reliable chemical methods for separation of organic and inorganic mercury, we used the Hg-R vs. Hg-NR rather than organic vs. inorganic division (Lindqvist and Rodhe 1985).\u003c/p\u003e\n\u003cp\u003eDetermination of total mercury in plankton, brine, bottom sediments, and pore waters was carried out using atomic absorption spectrometry \u003cem\u003eRA-915M\u003c/em\u003e (Lumex, Russia). Mercury contents in bottom sediments and pore waters were obtained down to a depth of 310 cm. Both unfiltered and filtered water samples for Hg assays were initially preconditioned using 1.5 mL of a 1:1 HNO\u003csub\u003e3\u003c/sub\u003e + H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e mixture added to 50 mL of sampled water. Then the solution, with 3\u0026ndash;4 drops of 5% KMnO\u003csub\u003e4\u003c/sub\u003e, was left overnight; excess KMnO\u003csub\u003e4\u003c/sub\u003e was removed with 10% hydroxylamine-sulfate (NH\u003csub\u003e2\u003c/sub\u003eOH)\u003csub\u003e2\u003c/sub\u003e\u0026bull;H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e added drop-by-drop until the solution became clear. Oxidation and extraction of mercury with KMnO\u003csub\u003e4\u003c/sub\u003e is commonly applied to environmental samples (Agemian and Chau 1976; Myagkaya et al. 2022). Reactive mercury species were analyzed using the method of Umezaki and Iwamoto (1971), in first-filtered samples (0.45 \u0026mu;m) with added 10 mL 2M H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, which were heated to 75\u0026ndash;80 \u0026deg;C in a water bath for 2\u0026ndash;3 h and cooled down; then the solution was diluted with distilled water to a volume of 50 mL. The concentrations of Hg-NR were determined in second-filter samples (0.45\u0026nbsp;\u0026mu;m) digested in a 1:1 HNO\u003csub\u003e3\u003c/sub\u003e + H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e mixture, from absorbance difference between Hg-susp and Hg-R after the flame atomic absorption spectroscopy (FAAS) assay. According to the specifications, the relative measurement error for Hg concentrations within the range of the analyzed samples was \u0026le;20% (p = 0.95) at a quantitation limit of 0.01 \u0026mu;g g\u003csup\u003e\u0026ndash;1\u003c/sup\u003e.\u0026nbsp;All samples were run in triplicate.\u003c/p\u003e\n\u003cp\u003eDetermination of inorganic compounds of Hg (II), Hg-OM and mercury sulfide (HgХ\u003csub\u003e2\u003c/sub\u003e, where X is Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e etc., and HgS) in bottom sediments was carried out by a direct hybrid method combining thermal analysis with atomic absorption detection \u003cem\u003eRA-915M\u003c/em\u003e (Shuvaeva et al., 2008). This technique allows you to determine some forms of mercury: stable (HgS и HgSe), labile (HgR\u003csub\u003e2\u003c/sub\u003e, were R is Cl, Br, O, SO\u003csub\u003e4\u003c/sub\u003e and thing lake that), toxic (methylmercury) and associated with organic matter (Hg-OM), for example, complex compounds with humic and fulvic acids.\u003c/p\u003e"},{"header":"3. Results","content":"\u003cp\u003e\u003cem\u003e3.1.\u0026nbsp;Lake and pore water chemistry\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe water of Lake Bolshoye Yarovoye belongs to the chloride class of sodium group, type III (Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e \u0026ge; Na\u003csup\u003e+\u003c/sup\u003e), by redox conditions \u0026mdash; to the oxidized type (Eh = +148...+26 mV), by alkaline-acid conditions \u0026mdash; to the weakly alkaline class (pH = 8\u0026ndash;8.2), by the value of total mineralization (138\u0026ndash;150 g L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e) \u0026mdash; to the family of brines (Table 1). Temperature stratification is observed in Lake Bolshoye Yarovoye with preservation of negative temperatures in summer. In August, the temperature of the surface layer of brine reached 21.6 \u0026deg;C, and at a depth of 4 m it was 18.5 \u0026deg;C. The water temperature at a depth of 8\u0026ndash;9 m can be negative and range from \u0026ndash;2 to \u0026ndash;5 \u0026deg;C (Solovyanova et al., 2022). The pH and Eh values change with depth in the lake waters (Table 1).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;1.\u003c/strong\u003e Hydrochemical parameters of surface and pore waters of Lake Bolshoye Yarovoye\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"671\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003eWater and core depth, cm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003epH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003eEh\u003c/p\u003e\n \u003cp\u003emV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eDIC\u003c/p\u003e\n \u003cp\u003emg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003eDOC\u003c/p\u003e\n \u003cp\u003emg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003eSO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003eCl\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003eg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003eFe\u003csub\u003etot\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003emg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003eMn\u003csub\u003etot\u003c/sub\u003e\u003c/p\u003e\n \u003cp\u003emg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003ePO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e\u003c/p\u003e\n \u003cp\u003emg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003eTDS mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003eEpilimnion, 50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e8.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e+148\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e89.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e40.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e5.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e79.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.090\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e1.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e138\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003eMetalimnion, 400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e8.17\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e+136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e94.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e36.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e5.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e87.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.096\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e1.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e147\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003eHypolimnion, 820\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e8.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e+26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e96\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e39.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e6.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e89.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.008\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.092\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e2.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e150\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003eWater\u0026mdash;sediment interface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e7.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;348\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e187.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e63.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e5.89\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e94.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.131\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e1.209\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e18.45\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e155\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003eUnconsolidated sediment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e7.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;384\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e235.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e44.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e5.74\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e98.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.124\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e1.392\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e17.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e161\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e0\u0026ndash;8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e7.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;329\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e79.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e9.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e89.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.051\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e2.343\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e162\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e20\u0026ndash;28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.90\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;310\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e10.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e92.09\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.045\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e2.093\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e1.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e165\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e32\u0026ndash;40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;356\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e65.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e51.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e10.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e94.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.039\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e2.026\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.93\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e167\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e50\u0026ndash;58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.87\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;322\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e14.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e101.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.323\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e1.51\u003c/p\u003e\n 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\u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e186\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e88\u0026ndash;104\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;327\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e77.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e63.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e15.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e100.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.006\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.562\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e185\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e112\u0026ndash;120\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e7\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e\u003cstrong\u003e01\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026ndash;367\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e75.1\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e47.3\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e10.58\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e97.80\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.021\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e1.338\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e2.45\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e181\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e140\u0026ndash;148\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.48\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;256\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e12.35\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e99.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.479\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e1.94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e179\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e170\u0026ndash;176\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;308\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e77.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e52.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e14.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e101.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.011\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.307\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e1.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e185\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e192\u0026ndash;200\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.53\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;360\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e61.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e77.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e19.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e109.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.016\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.201\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e2.80\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e206\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e231\u0026ndash;238\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;349\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e143.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e19.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e130.92\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.060\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.258\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e5.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e236\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e263\u0026ndash;269\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;358\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e141.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e18.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e133.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.064\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.358\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e3.57\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e236\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 117px;\"\u003e\n \u003cp\u003e306\u0026ndash;310\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 45px;\"\u003e\n \u003cp\u003e6.47\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e\u0026ndash;360\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e4.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e137.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e21.16\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e133.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.037\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 55px;\"\u003e\n \u003cp\u003e0.301\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e4.50\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e242\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eDOC \u0026mdash; dissolved organic carbon, DIC \u0026mdash; dissolved inorganic carbon. Fe\u003csub\u003etot\u003c/sub\u003e \u0026mdash; total dissolved iron, Mn\u003csub\u003etot\u003c/sub\u003e \u0026mdash; total dissolved manganese. TDS \u0026mdash; total dissolved solids. Dash \u0026mdash; no data.\u003c/p\u003e\n\u003cp\u003eA stratification of the chemical characteristics of water is also observed in the lake: from the surface to the bottom, there is an increase in DIC concentration, dissolved Fe, anions (SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e, Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e, PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e), and mineralization. A decrease in DOC in the depth of the water column is noted from 40.9 to 39.7 mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e. Mercury concentrations throughout the water column were below the detection limit. A significant increase in DIC, PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e, and dissolved Fe concentrations is observed at the water-sediment interface and in the unconsolidated sediment. The pH values decrease from 7.22 to 6.36 along the depth of bottom sediments (Table\u0026nbsp;1). The values of Eh vary from \u0026ndash;384 to \u0026ndash;230 mV, indicating strongly reducing conditions throughout the core. The pore waters show an increase in DOC, SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e, and Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e with depth. The pore waters of the first meter of sediment are characterized by a decrease in the content of dissolved Fe. A significant increase in dissolved Mn content from 0.09 to 2.4 mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e is observed within the upper 40 cm of the sediment. For the lower part of bottom sediments (230\u0026ndash;310 cm), there is a significant decrease in DIC from 62 to 5 mg/L and a strong increase in DOC (up to 143 mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e3.2.\u0026nbsp;Stratigraphy and mineral composition of bottom\u003c/em\u003e\u003cem\u003e\u0026nbsp;sediments\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe structure of bottom sediments of Lake Bolshoye Yarovoye is shown in Fig.\u0026nbsp;2a. The age of the bottom sediments is estimated at 7600\u0026plusmn;60 cal. years BP. According to our data, the calibrated age of the bottom sediments at a depth of 58\u0026ndash;60 cm is 2660\u0026plusmn;30 cal. years BP, which corresponds to the pre-industrial era. The bottom sediments are marly clays with relatively high content of terrigenous component (up to 85%) and carbonates (up to 22%). Iron concentrations along the core vary from 2.53 to 4.16% and average 3.63%. Manganese concentrations along the core vary from 356 to 614\u0026nbsp;ppm and average 480\u0026nbsp;ppm. Two types of bottom sediments can be distinguished: these are dark and watered hydrogen sulfide silt (density = 1.09 g/cm\u003csup\u003e3\u003c/sup\u003e, moisture content = 29.02%) located at the depth of 0\u0026ndash;182\u0026nbsp;cm, below this are lighter and denser lake sediments (density = 1.39 g/cm\u003csup\u003e3\u003c/sup\u003e, moisture = 21.77%).\u003c/p\u003e\n\u003cp\u003eThe modern lake deposits (0\u0026ndash;51\u0026nbsp;cm) consist of black mineralized sulfide muds (peloids). This interval is characterized by an increase in total Fe contents. Below (51\u0026ndash;72 cm) there are dark gray sulfide silts, which are characterized by a decrease in Fe. The interval from 72 to 104 cm has distinct boundaries and stands out visually. It is represented by gray silts, which mark the change in the conditions of lake sedimentogenesis. This is reflected in the chemical composition of the bottom sediments. The upper boundary of this interval has an increase in the terrigenous component and a decrease in carbonates. The lower boundary of this interval has a decrease in the terrigenous component and an increase in carbonates and Fe. The interval of 104\u0026ndash;182\u0026nbsp;cm are hydrogen sulfide silts similar to bottom sediments from the interval of 51\u0026ndash;72\u0026nbsp;cm. Further on there are sediments of another type, which are represented by gray-bluish dense clays. These sediments contain thin layers (0.2\u0026ndash;1\u0026nbsp;cm) of whitish, sometimes dark gray or dark green color. For this interval of bottom sediments, there is a trend of decreasing total iron content with depth.\u003c/p\u003e\n\u003cp\u003eAccording to XRD analysis, among the terrigenous minerals in the bottom deposits, quartz, illite, mica, and plagioclase dominate. In subordinate quantities, chlorite and smectite are present, while even fewer amounts of K-feldspars (potassium feldspars) and kaolinite are found. Amphibole is contained in trace amounts. Authigenic minerals identified include calcite, gypsum, and halite. At a depth of 302\u0026ndash;310\u0026nbsp;cm there are thin (up to 0.5\u0026nbsp;cm) and light layers with a large number of small crystals of gypsum and halite. Pyrite was detected in trace amounts in the 104\u0026ndash;112\u0026nbsp;cm interval. SEM data show the presence of pyrite framboids in the unconsolidated sediment (Fig.\u0026nbsp;2b). The Fe-Ti-Mn intermetallic (FeO = 45.14%, TiO\u003csub\u003e2\u003c/sub\u003e = 51.69%, MnO = 2.25%) were detected in the upper 5 cm of the sediment (Fig. 2c). They are apparently of a technogenic nature. Iron sulfides, represented mainly by pyrite, were found in the upper 5 cm of the sediment.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e3.3. Distribution of C, H, N, S in plankton and\u0026nbsp;\u003c/em\u003e\u003cem\u003ebottom\u003c/em\u003e\u003cem\u003e\u0026nbsp;sediments\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe content of total organic carbon (TOC) by bottom sediments depth varies from 1.12 to 2.23% (Fig.\u0026nbsp;3). The highest TOC contents (5.23%) were found in unconsolidated sediment and in zooplankton (Table\u0026nbsp;2). The distribution of hydrogen throughout the core is generally consistent and does not exceed 1%, except for unconsolidated sediment and the interval 109\u0026ndash;113\u0026nbsp;cm, where H values are 1.26% and 1.04%, respectively. Low nitrogen contents are characteristic of Lake Bolshoye Yarovoye throughout the core, being below the detection limit of the method, which is associated with the material composition of the bottom sediments (clays). Significant N contents were detected only in unconsolidated sediment and zooplankton, which amounted to 0.59 and 6.63%, respectively.\u003c/p\u003e\n\u003cp\u003eThe distribution of sulfur is not homogeneous throughout the depth of the core (Fig. 3).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;In the upper interval (0\u0026ndash;51 cm), S distribution is relatively consistent, ranging from 0.89 to 1.04%. Sulfur contents increase to 1.70\u0026ndash;3.28% in the 51\u0026ndash;130 cm. In the middle interval of 146\u0026ndash;181 cm, sulfur concentrations decrease to 1.20\u0026ndash;1.99%. In the lower interval (200\u0026ndash;310 cm), S contents increase to 2.51\u0026ndash;2.86%. The uneven distribution of sulfur against consistent TOC and H values likely reflects changes in intra-lake conditions throughout the Holocene period, such as fluctuations (increase/decrease) in lake salinity. An increase in reduced forms of sulfur (S (II)) is observed with depth (Fig. 3, Table 2).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;2.\u003c/strong\u003e Chemical composition of zooplankton, unconsolidated sediment (u.s.), and upper 5 cm of bottom sediments of Lake Bolshoe Yarovoye\u003c/p\u003e\n\u003cdiv align=\"center\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003eC, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003eH, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003eN, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003eS, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\"\u003e\n \u003cp\u003eS (II), %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003eHg\u003csub\u003etotal\u003c/sub\u003e, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003eHg-OM, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003eHgS+HgSe, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003eFe, %\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003eMn, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\n \u003cp\u003e\u003cem\u003eA. salina\u003c/em\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e37.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e5.81\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e6.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e1.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e0.28\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e0.058\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e185\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\n \u003cp\u003eU.s.\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e6.19\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e1.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e0.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e1.04\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e3.689\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e614\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 74px;\"\u003e\n \u003cp\u003e0\u0026ndash;5\u0026nbsp;cm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 56px;\"\u003e\n \u003cp\u003e2.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e0.84\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 51px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 52px;\"\u003e\n \u003cp\u003e0.98\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 53px;\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 57px;\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 69px;\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 84px;\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 59px;\"\u003e\n \u003cp\u003e3.959\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 54px;\"\u003e\n \u003cp\u003e539\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u0026lt;0.01 \u0026mdash; below the detection limit. Dash \u0026mdash; no data.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e3.4.\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003eReactive and non-reactive mercury in lake and pore water\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe concentration of the Hg-dc (dissolved + colloidal) fraction in lake water is below the detection limit (\u0026lt;0.02 ppm) (Table 3). Mercury in dissolved form is found only in unconsolidated sediment (0.07 ppm) and at the water\u0026mdash;sediment interface (0.15 ppm). At the water\u0026mdash;sediment interface, a predominance of non-reactive mercury specie (70%) over reactive Hg (30%) was found. There is a clear predominance of mercury in the suspended (Hg-susp) fraction over the Hg-dc fraction (almost 2-fold). The unconsolidated contains the highest amount of mercury in the Hg-dc fraction (0.17 ppm), of which more than 82% is in reactive specie.\u003c/p\u003e\n\u003cp\u003eThe concentration of suspended mercury fraction in the epilimnion (0.5 m) is below the detection limit. The presence of Hg-susp is found in the metalimnion (4.0) and hypolimnion (8.2 m) of the lake. With depth, an increase in suspended mercury 0.37 to 0.59 ppm is noted. In the metalimnion, more than 67% of mercury is in non-reactive\u0026nbsp;specie\u0026nbsp;(Hg-NR), while in the hypolimnion, Hg-NR accounts for only 44%, with the remaining 56% being reactive\u0026nbsp;specie\u0026nbsp;(Hg-R).\u0026nbsp;At the water\u0026mdash;sediment interface, the mercury content is 0.11 ppm, of which all Hg is in non-reactive\u0026nbsp;specie. No suspended mercury\u0026nbsp;fraction\u0026nbsp;was detected in the unconsolidated sediment and the underlying interval. Significant Hg-susp values of 37 ppm were found only in deep intervals of bottom sediments\u0026nbsp;(Table\u0026nbsp;3).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;3.\u003c/strong\u003e The fractions of mercury in surface and pore waters of Lake Bolshoye Yarovoye: dissolved + colloidal (Hg-dc) and suspended (Hg-susp)\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"100%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" style=\"width: 280px;\"\u003e\n \u003cp\u003eWater and core depth, cm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 194px;\"\u003e\n \u003cp\u003eHg-dc, \u0026micro;g L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd colspan=\"3\" style=\"width: 195px;\"\u003e\n \u003cp\u003eHg-susp, \u0026micro;g L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003eHg\u003csub\u003etotal\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003eHg-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003eHg-NR\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003eHg\u003csub\u003etotal\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003eHg-R\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003eHg-NR\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003eEpilimnion, 50\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003eMetalimnion, 400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.\u003c/strong\u003e\u003cstrong\u003e37\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.25\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003eHypolimnion, 820\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.59\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.26\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.33\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003eWater\u0026mdash;sediment interface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.07\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.04\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.11\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.11\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003eUnconsolidated sediment\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.17\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.03\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.14\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003e112\u0026ndash;120\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 280px;\"\u003e\n \u003cp\u003e300\u0026ndash;310\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 64px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 65px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 60px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.\u003c/strong\u003e\u003cstrong\u003e37\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.25\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 68px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.12\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eHg\u003csub\u003etotal\u003c/sub\u003e \u0026mdash; total mercury, Hg-R \u0026mdash; reactive mercury (non-organic), Hg-NR \u0026mdash; non-reactive mercury (organic). Dash \u0026mdash; no data.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e3.5. Distribution and species\u0026nbsp;\u003c/em\u003e\u003cem\u003eof mercury\u003c/em\u003e\u003cem\u003e\u0026nbsp;\u003c/em\u003e\u003cem\u003ein\u0026nbsp;\u003c/em\u003e\u003cem\u003eplankton\u003c/em\u003e\u003cem\u003e\u0026nbsp;and bottom\u003c/em\u003e\u003cem\u003e\u0026nbsp;sediments\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe mercury content in plankton is 0.28 ppm (Table 2) and in sediment varies from 0.01 to 4.5 ppm, averaging 2.3 ppm (Fig. 3). In unconsolidated sediment, the total mercury concentrations are 1.7 ppm. The distribution of mercury throughout the core is non-uniform, with three peaks identified: the first at a depth of 8\u0026ndash;11 cm (1.5\u0026ndash;2.3 ppm), the second in the interval of 26\u0026ndash;28 cm (0.9 ppm), and the third at a depth of 117\u0026ndash;119 cm (4.5 ppm). In the 120\u0026ndash;300 cm interval, mercury content decreases to 0.011\u0026ndash;0.8 ppm. At a depth of 300\u0026ndash;310 cm, mercury concentrations are below the detection limit. The upper part (0\u0026ndash;120 cm) of the bottom sediments is of particular interest as it accumulates Hg and undergoes changes in mercury\u0026nbsp;species (Fig.\u0026nbsp;3).\u003c/p\u003e\n\u003cp\u003ePreviously, the presence of anthropogenic mercury in the unconsolidated sediment of the lake was established. However, through the investigation of a long drilling core, the migration of Hg downwards through the profile of bottom sediments has been identified, reaching a depth of 120 cm (Fig.\u0026nbsp;3). In the interval of 117\u0026ndash;119\u0026nbsp;cm, there is an accumulation of mercury with an increase in its concentration by two orders of magnitude (from 0.04 to 4.5 ppm).\u003c/p\u003e\n\u003cp\u003eVarious forms of mercury occurrence have been identified in plankton (Table 2) and bottom sediments (Fig. 3). Plankton only demonstrates a concentration of Hg-OM at 0.28 ppm. Unconsolidated sediment exhibits the highest levels of Hg-OM at 1.1 ppm, accompanied by low concentrations of HgS+HgSe at 0.6 ppm. Within the upper section of bottom sediments (0\u0026ndash;4 cm), Hg-OM predominates, constituting up to 65%, compared to HgS+HgSe at 40%. Moving deeper into the sediment profile, there is an equitable distribution between Hg-OM (50%) and HgS+HgSe (50%). In the interval of 19\u0026ndash;51 cm, the proportion of Hg-OM increases to 52\u0026ndash;60%, subsequently decreasing to 30\u0026ndash;45% within the interval of 98\u0026ndash;113 cm. At a depth of 118\u0026ndash;120 cm, there is an increase in Hg-OM\u0026nbsp;specie\u0026nbsp;to 62%, accompanied by a decrease in HgS+HgSe. Notably, oxidized mercury species (HgR\u003csub\u003e2\u003c/sub\u003e) appear at 14% concentration within this interval. Apparently, HgR\u003csub\u003e2\u003c/sub\u003e is present throughout the section (especially in the upper intervals), but its concentrations are below the detection limit of the method (Shuvaeva et al., 2008). However, a local increase in total mercury within the 117\u0026ndash;118 cm interval enables the detection of all its forms, including HgR\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e"},{"header":"4. Discussion","content":"\u003cp\u003e\u003cem\u003e4.1. Water\u0026nbsp;\u003c/em\u003e\u003cem\u003emercury\u003c/em\u003e\u003cem\u003e\u0026nbsp;chemistry\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eMercury is a typical complexing agent and migrates in the form of complex compounds with ligands such as Cl\u003csup\u003e\u0026ndash;\u003c/sup\u003e, Br\u003csup\u003e\u0026ndash;\u003c/sup\u003e, I\u003csup\u003e\u0026ndash;\u003c/sup\u003e, HS\u003csup\u003e\u0026ndash;\u003c/sup\u003e, S\u003csup\u003e2\u0026ndash;\u003c/sup\u003e. Due to its strong affinity for Hg, chloride ion is a potentially important factor influencing the adsorption of mercury in salt lakes. According to physicochemical modeling data, inorganic forms of mercury in the brine of Lake Bolshoye Yarovoye are represented by chloride complexes: HgCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e = 92\u0026ndash;96%, HgCl\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e = 2.7\u0026ndash;5.9%, HgCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e = 0.25\u0026ndash;2.5% (Table 4). These complexes determine increased availability of Hg for biological objects, in particular for the halophilic crustacean \u003cem\u003eA. salina\u0026nbsp;\u003c/em\u003e(Leonova et al. 2007)\u003cem\u003e.\u003c/em\u003e Artemia concentrates up to 0.28 ppm of mercury in its composition (Table 2). According to Egorkina and Bender (2012) zooplankton inhabits nearly the entire water column (up to a depth of 7 m) of the lake, thus it can accumulate dissolved mercury from different depths.\u003c/p\u003e\n\u003cp\u003eThe ions of Hg are characterized by complexation with low molecular weight organic compounds and thiols (Beckers and Rinklebe 2017), which readily form complexes with mercury. These include both Hg\u003csup\u003e2+\u003c/sup\u003e and MeHg\u003csup\u003e+\u003c/sup\u003e. Low molecular weight thiols (such as mercaptoacetic acid, mercaptopropionic acid, cysteine, and glutathione) are formed under both oxidative and reductive conditions in hypolimnetic waters (Skyllberg 2012). The amount of DOC (Table\u0026nbsp;1), TOC, and\u0026nbsp;S\u0026nbsp;(Fig.\u0026nbsp;3)\u0026nbsp;is sufficient to form low molecular weight thiols.\u0026nbsp;Therefore, it would be erroneous to limit the presence of mercury only in chloride complexes. Our data on lake and pore water have been plotted on diagrams of prevailing mercury forms (Fig. 4). Mercury in inorganic complexes is present in the form of\u0026nbsp;HgCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e (Fig. 4a) and as Hg(SR)\u003csub\u003e2\u003c/sub\u003e (Fig. 4b), which was not previously considered in the thermodynamic modeling of the forms of mercury in the aqueous phase (Leonova et al. 2007). It is important to note that thiol groups are associated with dissolved organic matter (DOM), therefore under these conditions (Fig. 4c), mercury will be present more likely as MeHgSR-DOM than MeHgCl. It is important to emphasize that our data are in excellent agreement with the findings of Skyllberg (2012).\u003c/p\u003e\n\u003cp\u003eAnother source of mercury input into the lake ecosystem is suspended particulate matter. This is confirmed by the presence of suspended forms of mercury (Hg-susp) in the brine and the increase in Hg-susp with depth in the water column (Table 3). Mercury can enter the lake in suspension, adsorbed on clay minerals or OM; these could be technogenic formations, for example, the detected Fe-Ti-Mn intermetallics (Fig. 2c). This is because the deposition of solid particles is considered the main mechanism for delivering mercury to the water\u0026mdash;sediment interface, the main site of methylation. Diffusion (driven by redox potential) upwards from the sediment pore water is likely less significant (Ullrich et al. 2001).\u003c/p\u003e\n\u003cp\u003ePlankton and suspended particulate matter enter bottom sediments. Decomposition of planktonic organic matter and breakdown of mercury-containing clay minerals lead to the leaching of Hg into the pore water (Table\u0026nbsp;3), where it can sorb onto iron sulfides according to (Skyllberg et al. 2021). Further destruction of sulfides during diagenesis may result in mercury entering the pore water and accumulating Hg lower in the core at the sediment type transition zone (117\u0026ndash;119\u0026nbsp;cm). The active mineralization of planktonic organic matter in the 0\u0026ndash;11\u0026nbsp;cm layer is confirmed by a decrease in sediment pH and Eh, an increase in pore waters PO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e3\u0026ndash;\u003c/sup\u003e, DOC, and DIC, leading to the accumulation of dissolved Mn and Fe. The decrease in sulfate ions (SO\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e) and increase in dissolved iron forms in this interval, followed by their decrease down the core, indicate the processes of bacterial sulfate reduction and pyritization. These processes can contribute to the accumulation of mercury in sediment, which indirectly confirms the local increase in total Hg in the intervals of 10\u0026ndash;12\u0026nbsp;cm and 26\u0026ndash;28\u0026nbsp;cm. The increase of chloride in pore waters along the depth of the core (Table\u0026nbsp;1) may also favor the concentration of mercury in the bottom sediments.\u003c/p\u003e\n\u003cp\u003eThus, the accumulation of mercury in pore waters and at the water\u0026mdash;sediment interface indicates the mobility of Hg and its danger for the lake ecosystem.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.2. Sediment\u0026nbsp;\u003c/em\u003e\u003cem\u003emercury\u003c/em\u003e\u003cem\u003e\u0026nbsp;chemistry\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe accumulation of mercury in bottom sediments is typically attributed to the presence of clay minerals and organic matter (Beckers and Rinklebe 2017). The primary natural source of Hg in the sediments of Lake Bolshoye Yarovoye is predominantly aluminosilicate minerals (Malikova and Strakhovenko 2017), represented by quartz, illite, muscovite, and plagioclase. Clay minerals can also participate in mercury absorption, which is controlled by pH values. The pH influence both the surface charge characteristics of sediment particles and the dissolution/precipitation of metals (Beckers and Rinklebe 2017). Microbial decomposition of OM leads to a decrease in pH down the core from alkaline (pH 8.2) to slightly acidic (pH 6.4) values (Table 1). Changes in pH values can affect the concentration of mercury at local sediment sites, such as in the interval of 8\u0026ndash;27 cm (Fig. 3).\u003c/p\u003e\n\u003cp\u003eThe presence of organic or inorganic complexing agents also influences the geochemistry of mercury. The formation of soluble humic complexes can significantly increase the solubility and mobility of Hg in aquatic systems, especially at pH \u0026gt; 5 (Ullrich et al. 2001). Another important factor contributing to the concentration of mercury in bottom sediments is its complexation involving dissolved organic matter (Beckers and Rinklebe 2017). However, dissolved organic matter (DOC) appears to play an insignificant role in mercury concentration, as there is no correlation between the increase in DOC in pore waters and the increase in Hg in the bottom sediments. For example, where the interval of 231\u0026ndash;310 cm has the highest concentrations of DOC (137\u0026ndash;143 mg L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e), yet the mercury content in both the bottom sediments (Fig.\u0026nbsp;3) and pore waters (Table 3) is below the detection limit.\u003c/p\u003e\n\u003cp\u003eThe accumulation of mercury, both within bottom sediments and pore water, appears to be driven by the precipitation/dissolution dynamics of iron and manganese oxides and oxyhydroxides according to (Tisserand et al. 2022). In a study conducted by Malikova and Strakhovenko (2017), a positive correlation between Hg and Mn in the sediment of Lake Bolshoye Yarovoye was established. The notable surge in dissolved forms of Fe and particularly Mn observed in the upper sediment intervals (0\u0026ndash;40\u0026nbsp;cm) may indirectly signify processes involving the dissolution of iron and manganese oxides and oxyhydroxides under highly reducing conditions (Table\u0026nbsp;1). This phenomenon could potentially elevate the concentrations of dissolved mercury within the unconsolidated sediment and at the water\u0026mdash;sediment interface (Table\u0026nbsp;3).\u003c/p\u003e\n\u003cp\u003eIt is noteworthy that a correlation exists between the distribution patterns of sulfur forms, TOC, sediment grain size composition, and mercury content (including its chemical forms) within lake sediments, as highlighted by Ullrich et al. (2001) and Wang et al. (2022). The sulfur cycle within bottom sediments may be intricately linked to the formation of methylmercury (MeHg), as suggested by Wang et al. (2022). The mobility of Hg\u0026nbsp;(II) is governed by the formation of soluble polysulfides or organic complexes, as proposed by Ullrich et al. (2001). According to our findings, a correlation exists between the distribution of Hg-OM and S\u0026nbsp;(II) down to a depth of 51\u0026nbsp;cm; however, this correlation is not discernible beyond this depth (Fig.\u0026nbsp;3). This association is likely attributed to the activity of microorganisms, which have the capacity to influence mercury geochemistry (Manceau et al. 2015).\u003c/p\u003e\n\u003cp\u003eVarious physiological groups of microorganisms inhabit the water and sediments of Lake Bolshoe Yarovoe, including heterotrophic, halophilic, and non-spore-forming bacteria (Solovyanova et al. 2022). Studies have demonstrated the presence of sulfate reducers belonging to the Desulfobacterota taxon, as well as halophilic sulfidogenic bacteria from the genera Halanaerobium and Halomonas, capable of iron reduction under anaerobic conditions, in the sediments of the nearby saline Lake Maloe Yarovoe, situated 32\u0026nbsp;km to the northwest (Maltsev et al. 2023). Certain groups of sulfate-reducing and iron-reducing bacteria possess the ability to methylate mercury, converting dissolved inorganic mercury into MeHg, while also participating in the sulfur biogeochemical cycle within sediments, facilitating the mutual transformation of various forms of sulfur (Ullrich et al. 2001). Consequently, bacterial sulfate reduction occurring within the upper sediment intervals may lead to mercury accumulation. Active processes of bacterial sulfate reduction are indirectly corroborated by: i. the reduction in sulfate ion concentrations and dissolved iron (refer to Table\u0026nbsp;1); ii. an increase in total iron (see Fig.\u0026nbsp;2a) and S\u0026nbsp;(II) (refer to Fig.\u0026nbsp;3) within the bottom sediments; iii. the presence of iron sulfides (see Fig.\u0026nbsp;2b).\u003c/p\u003e\n\u003cp\u003eThe geochemistry of mercury within bottom sediments, encompassing both organic and inorganic forms, is subject to the influence of various sulfur compounds, including sulfate, sulfide, polysulfide, elemental sulfur (S\u003csup\u003e0\u003c/sup\u003e), and pyrite (FeS\u003csub\u003e2\u003c/sub\u003e), as elucidated by Skyllberg et al. (2021). Among these compounds, sulfide and polysulfide serve as potent ligands for Hg\u003csup\u003e2+\u003c/sup\u003e, thereby potentially restricting the biological availability of mercury and impacting the formation of methylmercury (MeHg). Consequently, the biogeochemical sulfur cycle within sedimentary deposits may exert a significant influence on MeHg formation (Wang et al. 2022). The formation of iron sulfides in the upper sediment intervals (Fig. 2b) may also contribute to the accumulation of mercury (Fig. 3).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cem\u003e4.3.\u0026nbsp;The ecological condition of the ecosystem of Lake Bolshoye Yarovoye (comparison with regional and global background)\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe mercury enrichment of mesoplankton in Lake Bolshoye Yarovoye, in the immediate vicinity of the \u0026ldquo;Altaikhimprom\u0026rdquo; chemical plant, increases several times (1.1\u0026ndash;2.3 ppm) compared to that in the background point on the opposite shore (0.46\u0026ndash;0.84 ppm), indicating the technogenic nature of high mercury concentrations in \u003cem\u003eA. salina\u003c/em\u003e. Plankton samples collected in August 2022 from the central part of the lake also showed lower Hg concentrations (0.28 ppm), which are comparable to mercury contents for \u003cem\u003eA. salina\u003c/em\u003e from salt lakes in the south of Western Siberia, particularly the Altai region (Table 5). In contrast, zooplankton from salt lakes in the European part of Russia contains an order of magnitude less Hg: from 0.029 to 0.096 ppm. Thus, the enrichment of zooplankton with mercury is determined not only by the geochemical specificity of the mineralized brine of Lake Bolshoye Yarovoye, as evidenced by the chemical forms of mercury (Table 4), but also by anthropogenic factors.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;4.\u003c/strong\u003e Percentages (%) of Hg and Fe species in brine of Lake Bolshoye Yarovoye (Leonova et al. 2007)\u003c/p\u003e\n\u003cdiv align=\"\"\u003e\n \u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"50%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eElement species\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 334px;\"\u003e\n \u003cp\u003eHg\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eHgCl\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eHgCl\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e2.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eHgCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e96.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" valign=\"top\" style=\"width: 334px;\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eFe(OH)\u003csub\u003e2\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e43.65\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eFe(OH)\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e0\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e55.41\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 171px;\"\u003e\n \u003cp\u003eFe(OH)\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e\u0026ndash;\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 163px;\"\u003e\n \u003cp\u003e0.94\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eSince mercury in the soils of the lake\u0026rsquo;s watershed averages 0.04 ppb (Malikova and Strakhovenko 2017), which is significantly below the maximum permissible concentrations set in Russia (2.1 ppb) (МРС, 2006), the main source of Hg is \u0026ldquo;Altaikhimprom\u0026rdquo; chemical plant. This was confirmed by our studies (Leonova et al. 2007). Further, mercury can infiltrate the lake environment where it is concentrated during filtration by mesozooplankton \u003cem\u003eA. salina\u003c/em\u003e, eventually depositing into the bottom sediments.\u003c/p\u003e\n\u003cp\u003eIn our opinion, the main diffuse sources of technogenic mercury entering the lake are the coastal dumps of solid waste from the \u0026ldquo;Altaikhimprom\u0026rdquo;, especially during the snowmelt period, which is consistent with the data of other researchers (Temerev et al. 2002). However, the concentration of Hg in the water of Lake Bolshoye Yarovoye is lower than in regional salt lakes, as well as salt lakes in the European part of Russia and America (Table 5). This indicates that the input of \u0026ldquo;technogenic\u0026rdquo; mercury into lake mainly occurs in suspended form (Table 3). This does not lead to the accumulation of mercury in the lake water. Mercury is concentrated in plankton (especially in the vicinity of the plant) and bottom sediments, for which Hg contents (up to 4.5 ppm) are higher than in other saline water bodies with higher mercury contents (Table 5). This could pose an ecological risk to the ecosystem of Lake Bolshoye Yarovoye.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;5.\u003c/strong\u003e Mercury content in water, Artemia and bottom sediments of salt lakes in Russia and the world\u003c/p\u003e\n\u003ctable border=\"0\" cellspacing=\"0\" cellpadding=\"0\" width=\"662\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eLake / region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003eSalinity, g\u0026nbsp;L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003eHg in water \u0026micro;g L\u003csup\u003e\u0026ndash;1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003eHg in artemia, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003eHg in sediments, ppm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eReference\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" style=\"width: 662px;\"\u003e\n \u003cp\u003eRussia, south of Western Siberia\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eBolshoye Yarovoe,\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eAltai region\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e138\u0026ndash;150\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026lt;0.0\u003c/strong\u003e\u003cstrong\u003e1\u0026ndash;\u003c/strong\u003e\u003cstrong\u003e0.0\u003c/strong\u003e\u003cstrong\u003e4*\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.28\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e0.01\u0026ndash;4.5\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003e\u003cstrong\u003eOur data (2022)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eKulundinskoe,\u003cbr\u003e\u0026nbsp;Altai region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e94\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd rowspan=\"2\" style=\"width: 142px;\"\u003e\n \u003cp\u003eLeonova et al. 2007\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eMaloye Yarovoe,\u003cbr\u003e\u0026nbsp;Altai region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e262\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eBolshoy Bagan, Novosibirsk region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e282\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e\u0026lt;0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.0013\u0026ndash;0.022\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eOur data (2019)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" style=\"width: 662px;\"\u003e\n \u003cp\u003eEuropean Russia\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eKiyatskoe,\u003cbr\u003e\u0026nbsp;Crimea\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.020\u0026ndash;0.363\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eMirzoyeva et al. 2015\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eKirleutskoye,\u003cbr\u003e\u0026nbsp;Crimea\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e190\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.019\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.029\u0026ndash;0.096\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eEvstafeva et al. 2021;\u003cbr\u003e\u0026nbsp;Shadrin et al. 2022\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eAktashskoe,\u003cbr\u003e\u0026nbsp;Crimea\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e214\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.022\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e0.038\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.011\u0026ndash;0.026\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eStetsyuk et al. 2018;\u003cbr\u003e\u0026nbsp;Shadrin et al. 2022\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" style=\"width: 662px;\"\u003e\n \u003cp\u003eWorld objects\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eThe Great Salt Lake, Utah, USA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.005\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.5\u0026ndash;1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eWurtsbaugh\u0026nbsp;et al. 2020;\u003cbr\u003eWright et al. 2020\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd style=\"width: 162px;\"\u003e\n \u003cp\u003eDevils,\u003cbr\u003e\u0026nbsp;North Dakota, USA\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 76px;\"\u003e\n \u003cp\u003e11\u0026ndash;25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 83px;\"\u003e\n \u003cp\u003e0.04\u0026ndash;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 94px;\"\u003e\n \u003cp\u003e\u0026mdash;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 104px;\"\u003e\n \u003cp\u003e0.005\u0026ndash;0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd style=\"width: 142px;\"\u003e\n \u003cp\u003eSwenson and Colby 1954;\u003cbr\u003e\u0026nbsp;Lent and Alexander 1997\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eDash \u0026mdash; no data, \u0026lt;0.01 \u0026mdash; less than detection limit, * \u0026mdash; according to Leonova et al. 2007.\u003c/p\u003e"},{"header":"5. Conclusions","content":"\u003cp\u003ei.\u0026nbsp;Mercury primarily exists in inorganic complexes in the form of HgCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e and Hg(SR)\u003csub\u003e2\u003c/sub\u003e. In both lake and pore waters, mercury is predominantly found in the form of MeHgSR-DOM rather than MeHgCl.\u003c/p\u003e\n\u003cp\u003eii.\u0026nbsp;Dissolved organic matter exhibit negligible influence on mercury concentration within the sediment of Lake Bolshoye Yarovoye. Instead, the accumulation of mercury in bottom sediments is attributed to the precipitation/dissolution processes oxides and oxyhydroxides of Fe and Mn.\u003c/p\u003e\n\u003cp\u003eiii.\u0026nbsp;The geochemistry of mercury within bottom sediments, encompassing both organic and inorganic forms, is subject to the influence of various sulfur compounds, including sulfate, sulfide, polysulfide, elemental sulfur, and pyrite. Sulfide and polysulfide serve as potent ligands for Hg\u003csup\u003e2+\u003c/sup\u003e, thereby potentially restricting the biological availability of mercury and impacting the formation of methylmercury.\u003c/p\u003e\n\u003cp\u003eiv.\u0026nbsp;Within the upper 50\u0026nbsp;cm of sediment, a correlation exists between the distribution of Hg-OM and S\u0026nbsp;(II). This correlation is linked to the activity of sulfate-reducing microorganisms.\u003c/p\u003e\n\u003cp\u003ev.\u0026nbsp;The vertical migration of technogenic mercury in the sediment core due to its high water content has been identified. At a depth of 110\u0026ndash;120\u0026nbsp;cm, a geochemical barrier emerges, characterized as a zone of active transformation of mercury forms. A geochemical barrier is formed by a combination of processes such as sorption on clay minerals and organic matter, as well as alterations in sediment density.\u003c/p\u003e\n\u003cp\u003evi. By employing a set of geochemical criteria, it has been deduced that there exists moderate mercury contamination within the bottom sediments and mesoplankton of Lake Bolshoye Yarovoye within the influence zone of the \u0026ldquo;Altaikhimprom\u0026rdquo; plant. The primary source of diffuse technogenic mercury influx into the lake stems from the coastal solid waste dumps of the plant, particularly during the snowmelt period.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCRediT authorship contribution statement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eMaria Gustaytis\u003c/strong\u003e\u003cstrong\u003e:\u003c/strong\u003e Conceptualization, Writing\u0026mdash;original draft preparation, Methodology, Investigation. \u003cstrong\u003eAnton Maltsev:\u003c/strong\u003e Conceptualization, Editing, Investigation, Fieldwork. \u003cstrong\u003eGalina Leonova:\u003c/strong\u003e Methodology, Supervision. \u003cstrong\u003eSergey Krivonogov:\u003c/strong\u003e Funding, Fieldwork. The first draft of the manuscript was written by \u003cstrong\u003eMariya Gustaytis\u003c/strong\u003e and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no conflict of interest.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData will be made available on request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe analytical studies were carried out in the Analytical Center for multi-elemental and isotope research SB RAS. Work is done on state assignment of V.S.\u0026nbsp;Sobolev Institute of Geology and Mineralogy Siberian Branch Russian Academy of Sciences, Projects No 122041400193-7 and No 122041400252-1.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe greatly appreciate cooperation with our colleagues who performed analytical work: determination of total mercury by N.V. Androsova and the X-ray powder diffraction (XRD) analysis by L.V. Miroshnichenko from the Sobolev Institute of Geology and Mineralogy SB RAS (Novoibirsk).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAgemian H, Chau A S Y, (1976) An improved digestion method for the extraction of mercury from environmental samples. Analyst 101 (1199): 91\u0026ndash;95.\u003c/li\u003e\n\u003cli\u003eBeckers F, Rinklebe J (2017) Cycling of mercury in the environment: Sources, fate, and human health implications: A review. 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Mine Water and the Environment 41 (2): 437\u0026ndash;457. https://doi.org/10.1007/s10230-022-00859-6\u003c/li\u003e\n\u003cli\u003eMalikova I N, Ustinov M T, Anoshin G N, Badmaeva Zh O, Malikov Yu I, (2008) Mercury in soils and plants in the area of Lake Bol\u0026rsquo;shoe Yarovoe (Altai Territory). Russian Geology and Geophysics 49 (1): 46\u0026ndash;51. https://doi.org/10.1016/j.rgg.2007.12.004\u003c/li\u003e\n\u003cli\u003eMalikova I N, Strakhovenko V D, (2017) Correlations between Mercury in Soils and Bottom Deposits of Bol\u0026apos;shoye Yarovoye Lake. Chemistry for sustainable development 25 (2): 191\u0026ndash;198. DOI: 10.15372/KhUR20170211\u003c/li\u003e\n\u003cli\u003eMaltsev A E, Safonov A V, Leonova G A, Krivonogov S K, (2023) Biogeochemistry of Holocene sediments of the bitter-salty lake Maloye Yarovoye (Altai Territory). In: Modern development of biogeochemical ideas V.I. Vernadsky. Non-governmental environmental foundation V.I. Vernadsky, Moscow: 310\u0026ndash;320. (In Russian)\u003c/li\u003e\n\u003cli\u003eManceau A, Lemouchi C, Enescu M, Gaillot A C, Lanson M, Magnin V, Glatzel P, Poulin B A, Ryan J N, Aiken\u003csup\u003e \u003c/sup\u003eG R, Gautier-Luneau I Nagy K L (2015). Formation of mercury sulfide from Hg (II)\u0026ndash;thiolate complexes in natural organic matter. Environmental Science \u0026amp; Technology, 49(16): 9787-9796. DOI: 10.1021/acs.est.5b02522\u003c/li\u003e\n\u003cli\u003eMason R P, Fitzgerald W F, Hurley J, Hanson Jr A K, Donaghay P L, Sieburth J M, (1993) Mercury biogeochemical cycling in a stratified estuary. Limnology and Oceanography, 38(6): 1227-1241.\u003c/li\u003e\n\u003cli\u003eMirzoyeva N, Gulina L, Gulin S O, Stetsuk A, Arkhipova S, Korkishko N, Eremin O, (2015) Radionuclides and mercury in the salt lakes of the Crimea. Chin. J. Ocean. 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Science of the Total Environment, 749: 141273. https://doi.org/10.1016/j.scitotenv.2020.141273\u003c/li\u003e\n\u003cli\u003eWurtsbaugh W A, Leavitt P R, Moser K A, (2020) Effects of a century of mining and industrial production on metal contamination of a model saline ecosystem, Great Salt Lake, Utah. Environmental Pollution 266: 115072. https://doi.org/10.1016/j.envpol.2020.115072\u003c/li\u003e\n\u003cli\u003eZhu S, Zhang Z, Zagar D, (2018) Mercury transport and fate models in aquatic systems: a review and synthesis. Sci. Total Environ. 639: 538\u0026ndash;549. https://doi.org/10.1016/j.scitotenv.2018.04.397\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Mercury, Methylmercury, Mercury species, Sulfur, Mercury biogeochemistry, Hyperhaline lake, Western Siberia","lastPublishedDoi":"10.21203/rs.3.rs-6909634/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6909634/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe investigation focused on examining the concentration of mercury in the brine, plankton, and bottom sediments of Lake Bolshoye Yarovoye. Mercury in inorganic complexes primarily exists in the forms of HgCl\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e2\u0026ndash;\u003c/sup\u003e and Hg(SR)\u003csub\u003e2\u003c/sub\u003e. Within lake and pore waters, mercury will be present as MeHgSR-DOM rather than MeHgCl. Accumulation of mercury in bottom sediments ensues from the precipitation/dissolution processes oxides and oxyhydroxides of Fe and Mn. The geochemical behavior of mercury in sediments is subject to the influence of various sulfur compounds, including S (VI), S (II), S\u003csup\u003e0\u003c/sup\u003e, and pyrite, which possess the capacity to constrain the bioavailability of mercury and impact the formation of MeHg. A correlation is noted in the distribution of Hg-OM and S (II) within the upper 50 cm of sediment. The vertical migration of technogenic mercury in the sediment core due to its high water content has been identified. At a depth of 110\u0026ndash;120 cm, a geochemical barrier emerges, characterized as a zone of active transformation of mercury forms. A moderate level of mercury contamination has been observed in bottom sediments and plankton \u003cem\u003eArtemia salina\u003c/em\u003e within the influence zone of the \u0026ldquo;Altaikhimprom\u0026rdquo; plant.\u003c/p\u003e","manuscriptTitle":"Mercury species in zooplankton, brine, and bottom sediments of hyperhaline Lake Bolshoye Yarovoye (south of Western Siberia)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-08-19 12:24:12","doi":"10.21203/rs.3.rs-6909634/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-10-06T14:47:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-28T12:46:26+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"250607059629623111004778805983716150897","date":"2025-09-04T07:07:38+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-09-04T04:09:20+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"207305901548112080452738045999771786961","date":"2025-09-03T17:42:21+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"159144427953403803663982402356998229512","date":"2025-08-14T11:22:57+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-08-11T10:23:26+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-18T03:45:10+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-18T03:44:05+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Earth Sciences","date":"2025-06-17T02:50:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-earth-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"enge","sideBox":"Learn more about [Environmental Earth Sciences](https://www.springer.com/journal/12665)","snPcode":"12665","submissionUrl":"https://submission.nature.com/new-submission/12665/3","title":"Environmental Earth Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"d500018a-5c18-4a87-a0aa-86c42f8c3394","owner":[],"postedDate":"August 19th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-29T16:05:54+00:00","versionOfRecord":{"articleIdentity":"rs-6909634","link":"https://doi.org/10.1007/s12665-025-12735-x","journal":{"identity":"environmental-earth-sciences","isVorOnly":false,"title":"Environmental Earth Sciences"},"publishedOn":"2025-12-24 15:57:18","publishedOnDateReadable":"December 24th, 2025"},"versionCreatedAt":"2025-08-19 12:24:12","video":"","vorDoi":"10.1007/s12665-025-12735-x","vorDoiUrl":"https://doi.org/10.1007/s12665-025-12735-x","workflowStages":[]},"version":"v1","identity":"rs-6909634","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6909634","identity":"rs-6909634","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}