Dissolved Ba as discriminator between two adjacent karst catchments that are both subject to allogenic recharge (Sohodol valley, Vâlcan Mountains, Romania)

Dissolved Ba as discriminator between two adjacent karst catchments that are both subject to allogenic recharge (Sohodol valley, Vâlcan Mountains, Romania) | 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 Dissolved Ba as discriminator between two adjacent karst catchments that are both subject to allogenic recharge (Sohodol valley, Vâlcan Mountains, Romania) Nicolae Cruceru, Horia Mitrofan, Constantin Marin, Marius Vlaicu, and 4 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4317845/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 28 Nov, 2024 Read the published version in Environmental Earth Sciences → Version 1 posted 3 You are reading this latest preprint version Abstract In a fluviokarst region, three seldom used natural tracers, SiO 2 , Na and Ba, were considered for tracking the allogenic, silicate-derived water contribution to cave streams and to final karst outflows. The concerned allogenic recharge originates in watersheds that consist of metamorphic formations intruded by magmatic rocks, for which available whole rock chemistry data indicate rather uniform contents of SiO 2 and Na, but contrasting (up to one order of magnitude) contents of Ba. All three considered natural tracers proved to behave, along karst flowpaths, conservatively, and indicated binary mixing between allogenic and autogenic inputs. However, only the dissolved Ba concentrations enabled chemical distinction to be made between two separate, adjacent karst catchments: one having allogenic inputs presumably derived mainly from the weathering of Ba-rich rocks (essentially granites), while the other had allogenic recharge originating mostly in the weathering of Ba-poor formations. In contrast, if only the sampled waters SiO 2 and Na concentrations had been considered, it would have been virtually impossible to establish if the two adjacent karst catchments were distinct - or not - from each other. When considering each of the two karst catchments separately, the concentrations distribution of each of the three natural tracers, SiO 2 , Na and Ba, consistently indicated that between a swallet and a connected cave stream, then further between cave streams and final karst outflows, the allogenic water relative contribution gradually diminished to the benefit of autogenic water. karst allogenic recharge hydrochemistry natural tracers barium Romania Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Introduction A basic type of karst landscape includes, as main features, valleys which had initially been shaped by surface streams. Subsequently, the corresponding river courses were captured in valley-bottom swallets, that conveyed the water flow to underground conduits developed by dissolution in a carbonate rocks substratum. Such a setting is designated (e.g., Smart 1988; Taylor and Greene 2008; Phillips 2017) as fluviokarst - in contrast to holokarst , a landscape that essentially consists of closed depressions formed by dissolution, and which is virtually devoid of any stream channels. Fluviokarst is in many instances related (e.g., Jennings 1982; Bočić 2003; Bočić and Baćurin 2004; Anthony ad Granger 2007; Mihevc 2007; Herman et al. 2012) to stream catchments whose headwaters are incised in a non-carbonate substratum, while the downstream reaches develop within carbonate rocks (the latter formations being those which had favoured the stream piracy in the underground). In such multi-lithological settings, the karst groundwater chemical composition is largely controlled (e.g., Petelet et al. 1998; Qin et al. 2017; Gill et al. 2018; Lorette et al. 2021; Fernández‑Ortega et al., 2023) by mixing between two main inputs: (i) water associated to the weathering of non-carbonate (usually silicate) formations, and which provides allogenic recharge to the karst areas situated downgradient, and (ii) autogenic recharge water, which dissolves the carbonate rock bodies that host the actual underground karst flowpaths. In order to discriminate between those two contributing water types, in the present study there have been selected three natural inorganic chemical tracers: Na, SiO 2 and Ba. Provided that no evaporite deposits or of anthropic pollution sources, Na was previously noticed to originate almost exclusively (e.g., Han and Liu 2004; Ma et al. 2011; Pu et al. 2012; Qin et al. 2017; Petalas and Moutsopoulos 2019) in silicate rocks weathering (dissolution of feldspars or other silicate minerals), while only a negligible amount of Na was released from limestone or dolomite dissolution. Therefore Na has been used on several occasions (Qin et al. 2017; Guo et al. 2019) for tracking water inflows from surface streams into karst aquifers. In contrast, SiO 2 has been only seldom considered as a possible natural tracer in karst environments with allogenic recharge. This circumstance is rather surprising, given that one would normally expect the dissolved SiO 2 content of silicate-derived (allogenic) water to be conspicuously larger than the content of the carbonate-derived (autogenic) inputs. Yet an example from the Upper Floridan aquifer (Katz et al. 1998) illustrates an opposite situation, in which a sinking river had a significantly lower SiO 2 concentration than pristine carbonate-derived groundwater which was sampled, under low flow conditions, from the karst aquifer. Another example of SiO 2 concentrations progressively increasing from the recharge toward the discharge zones was provided by Ma et al. (2011) for a karst aquifer in northern China. The dissolved silica enrichment has been ascribed in that case to higher temperatures acquired by water which before resurfacing in the discharge zone, had circulated along deep (up to 2 km) flowpaths. Other reports of silica abundances in karst waters (e.g., Lastennet and Mudry, 1997; Díaz-Puga et al. 2016; Denimal et al. 2017) have addressed settings virtually devoid of any allogenic recharge, hence the corresponding results cannot be directly compared to those of the present investigation. Like in the case of SiO 2 , few reports exist so far (Molina-Porras et al. 2017; Gill et al. 2018; Petalas and Moutsopoulos 2019) concerning the utilization of the minor element Ba as natural tracer in karst environments with allogenic recharge. Yet in the area considered by the present study, Ba proved to be, out all analysed constituents, the only one being able to properly discriminate between two distinct karst catchments. Extended areas within the watersheds which provide allogenic recharge to those catchments are occupied by magmatic intrusions, whose chemical composition specificities (reported in Savu et al. 1971, 1974; Féménias et al. 2008) were taken into account in an attempt to explain the recorded particular behaviour of Ba. In the present investigation, advantage has also been taken of the conservative behaviour which had been previously outlined in karst environments for Na (Petelet at al. 1998; Qin et al. 2017; Gill et al. 2018), SiO 2 (Katz et al. 1998) and Ba (Molina-Porras et al. 2017; Gill et al. 2018). Consequently, those tracers’ concentration values were used in the present study for constructing bivariate plots that provided information on: binary mixing patterns mirroring hydrological connections along underground flowpaths; relative contributions of the allogenic and autogenic inputs along those flowpaths. An approach somehow similar to that of Gill et al. (2018) and Lorette et al. (2021) was adopted, by focusing on geochemical signatures associated to underground flowpaths along which the relative contribution of autogenic inputs (originating in diffuse infiltration through the limestone body) progressively increased, to the detriment of the allogenic water contribution: starting from swallets supplied by silicate rock watersheds, toward streams intercepted in underground conduits, and further to the final karst outflows. Eventually, consistent estimates of the allogenic water fraction discharged by the considered major karst outflows have been provided by the concentrations of Na and SiO 2 (and sometimes, also by the Ba contents). Overall, the obtained results could represent initial assessments concerning the ability of the three considered natural tracers to elucidate underground drainage patterns within karst catchments subject to allogenic recharge. Physiographic and geological setting The present study addresses a fluviokarst region in Vâlcan mountains (South Carpathians range), within the catchment of Sohodol valley (Fig. 1 ). It is a rugged topography area, with several peaks ranging between 1400 and 1500 m a.s.l., while only one, Şigleul Mare, reaches almost 1700 m a.s.l.). On the other hand, the streambed of the Sohodol main valley descends, at its exit from the considered karst domain, down to 400 m a.s.l.. Most part of the considered catchment is covered by beech forests, grassland usually occupying only some of the highest peaks and ridges. The climate is temperate, with a mean annual temperature that declines from 8–9°C at the mountain front, down to about 2°C on the highest ridges. Average annual rainfall amounts to about 900 mm at the mountain front, increasing to 1200–1400 mm at higher altitudes. Two rainfall peaks occur, totalling 130–150 rainfall days/year: the main peak is recorded during March-May, and the secondary one in November-December. Snow falls occur during the cold season, with the snow layer usually lasting for 100–150 days (all indicated climate data are according to Muică 1995). Sudden temperature increases toward the end of February and in March result (Neamu 1998) in early snowmelt that triggers flash floods. All rock formations in the Sohodol watershed belong to a single geological unit, the Lainici Nappe (Berza et al. 1994; Liégeois et al. 1996), whose basement includes two polymetamorphic groups (Berza 1978) of Late Precambrian age. The more recent, metasedimentary Lainici-Păiuş Group includes a lower “Carbonate-Graphitic Formation” underlying an upper “Quartzitic and Biotite Gneiss Formation” (Liégeois et al. 1996). In addition, three types of magmatic intrusions were distinguished within the metamorphic formations: (i) dykes and bodies consisting of Late Precambrian leucogranitoids (Liégeois et al. 1996); (ii) Late Precambrian granites and granodiorites building up large plutons (Savu et al., 1971; Berza, 1978); (iii) Early Paleozoic (Pre-Silurian) dykes and sills (“Motru Dyke Swarm”) which include mainly andesites and basaltic andesites (Féménias et al., 2008). Overall, two thirds of the Lainici-Păiuş Group occurrence area was estimated to be occupied by granitoids (Berza 1978), yet a thorough cartographic representation of this setting was provided only for the large Precambrian plutons (Fig. 1 ). The older, metavolcanic Drăgşan Group includes (Berza et al. 1994; Liégeois et al. 1996) an Amphibolite Formation (consisting mainly of banded amphibolites). It is widely developed in the hanging wall of a major reverse fault that brings the amphibolites in contact with the Lainici-Păiuş Group (Stan et al. 1979; Berza et al. 1994). It has been however presumed (Berza, 1978) that Drăgşan metamorphics could be present also underneath the Lainici-Păiuş metasediments. A Paleozoic cover common to both metamorphic groups includes (Stan et al., 1979) low grade formations consisting of chlorite and sericite schists (belonging to the Ordovician and Devonian time-interval), and of carbonate and graphitic rocks (of Carboniferous age). The Mesozoic cover of the Lainici Nappe starts (Stan et al. 1979; Berza et al. 1994) with Early Jurassic siliciclastic deposits in Gresten facies (conglomerates, sandstones and shales). They are overlain by a thick carbonate series (various kinds of limestones, occasionally dolomitized – Pop 1973) that was deposited during the Middle Jurassic-Early Cretaceous (Aptian) interval, and which hosts the karst features concerned by the present study. The carbonate series is transgressively covered by Middle-Late Cretaceous clastics, some of which are intruded by ophiolite veins and dykes (Stan et al. 1979). Locally, Middle Jurassic-Early Cretaceous carbonates also occur in a thrust sheet that tectonically overlies Middle-Late Cretaceous clastics. The watersheds at the headwaters of Sohodol trunk stream and of its main tributaries (Măcriş, Şipot, Gropu Sec, Scărişoara, Gropu cu Apă) are developed, over 72 km 2 , within terrains that include the Lainici Nappe metamorphic and granitic basement and its Paleozoic low-grade cover formations. The indicated stream courses next enter an extended surface occupied mainly by Mesozoic carbonate rocks, where the subsequent 42 km 2 of watersheds occur. The carbonate rocks domain is yet rendered more complex by of an uplifted, island-shaped granite body, which crops out over about 4 km 2 and accordingly imposes restricted pathways to the limestone-hosted underground flows along Sohodol valley (Fig. 1 ). Sampling sites selection relying on previous information about karst hydrology Karst drainage features within the concerned section of Sohodol valley have been discussed in a paper published by Iurkiewicz and Mangin (1994). Based on their investigations, they conjectured that a common groundwater flow system was discharging via two large perennial karst springs, Pătrunsa (PAT) and Picuiel (PIC), both located on the right side of Sohodol valley (Table 1 , Fig. 1 ). It was additionally stipulated that Fuşteica (FUS) impenetrable swallet - where Sohodol stream itself loses in its right-side bank part (and in drought periods, the entirety) of its discharge - contributed to the supply of the same groundwater flow network. Moreover, about 300 m downstream FUS swallet, and also on the right side of the valley, it is situated the Cave Downstream Fuşteica Swallet, whose fossil passages intercept, about 500 m after the entrance, an underground stream (sampling point CFUS - Table 1 , Fig. 1 ), which flows into a sump. Table 1 The sampling sites within the investigated karst area of Sohodol valley side of Sohodol Type Name code Latitude N Longitude E elevation (m a.s.l) estimated flow rate a (L/s) sampling Oct 2023 May 2023 Mar 2023 Nov 2022 Oct 2022 right impenetrable swallet Fuşteica FUS 45°12'29.29" 23° 7'54.96" 516 250 x x x cave intercepting an underground stream Downstream Fuşteica Swallet CFUS b 45°12'21.74" 23° 7'52.17" 525 n.e. x x major impenetrable spring with assumed allogenic supply Picuiel PIC 45°10'37.97" 23° 7'59.02" 425 100–200 x x x Pătrunsa PAT 45°10'44.40" 23° 7'56.43" 430 100–500 x x small impenetrable spring with no allogenic input Piva PIV 45°11'43.80" 23° 3'13.61" 910 1–10 x x left cave intercepting an underground stream At the Mouth of Valea Rea CVAR b 45°10'22.82" 23° 8'10.81" 415 n.e. x x impenetrable spring with assumed allogenic supply Valea Rea VAR 45°10'23.71" 23° 8'10.53" 410 n.e. x x x small impenetrable spring with no allogenic input Travertine at Picuiel TRAP 45°10'41.40" 23° 7'59.90" 430 n.e. x x a - according to Iurkiewicz and Mangin (1994) b - the indicated coordinates correspond to the cave entrance n.e. - not estimated Iurkiewicz and Mangin (1994) have published details of an artificial tracer test which had substantiated the interconnection between PIC and PAT springs, but no specific information was provided about tracer tests having checked if FUS swallet (and/or CFUS cave stream) were linked to PAT and PIC major outflows. In the framework of the present study, water samples have been collected from all the above-indicated sites located on the right side of Sohodol. There have been sampled in addition two sites situated on the valley left side (Table 1 , Fig. 1 ): Valea Rea (VAR) impenetrable perennial spring, which has a far less abundant flow rate than either PAT, or PIC outflows; the underground stream intercepted in the Cave at the Mouth of Valea Rea, which is positioned quite close to VAR spring and about 5 m above it. A 40 m long streamlet (sampling point CVAR) permanently flows along the cave passage, to eventually discharge by the cave entrance. Iurkiewicz and Mangin (1994) have not dedicated any discussion to the latter two sites, and no artificial tracer test has addressed possible hydrological links that could involve VAR spring and/or CVAR cave stream. In an attempt to develop and expand the overall karst drainage model previously formulated by Iurkiewicz and Mangin (1994), the present study aimed to identify hydrochemical evidence that would contribute to elucidate underground hydrological connections which involved the six above-indicated sampling sites. At the same time, central to the present investigation was the circumstance that the relative contributions of the allogenic and autogenic water inputs differed between one sampling site and another. Specifically, since metamorphic and granitic formations built up most of the watershed supplying FUS swallet (Fig. 1 ), its sinking flow was considered to have a chemical composition largely representative for allogenic, silicate-derived water. Alternatively, it was reasonable o assume that each of the two springs PAT and PIC, and possibly also CFUS cave stream likely consisted of silicate-carbonate water mixtures. Moreover it was assumed, as a first order approach, that also VAR spring and CVAR cave stream discharged a mixture consisting of various proportions of silicate (allogenic) and carbonate (autogenic) water. Investigating the mixing process between allogenic and autogenic inputs also required some information on the chemistry of the pristine carbonate-derived (i.e. autogenic) water. Identifying sampling sites presumably representative in this respect was however not straightforward. One such site was conjectured to be the small perennial karst spring Piva (PIV), which discharged (Fig. 1 ) from a limestone body isolated on a mountain top that was devoid of any allogenic water inputs. Since large amounts of travertine were noticed to have precipitated from PIV outflow, analogous deposits associated to another small perennial spring (TRAP), were assumed to indicate that also its water was exclusively carbonate-derived. It is still important to emphasize that in the case of TRAP spring, a hydrological connection with the other sampled sites is highly unlikely, while in the case of PIV spring, such a link is just impossible: those two small springs can therefore be viewed only as proxies of the carbonate-derived (autogenic) water which was assumed to be actually involved in the supply of PAT, PIC and VAR springs and of the CFUS and CVAR cave streams. Sampling and analytical procedures A sampling operation including all the previously discussed sites (Table 1 ) has been conducted on 14–15 October 2023, during a low water stage. Some of the concerned sites, located on the right side of Sohodol valley, had been sampled also on 6–7 May 2023 (high water conditions) and on 29 Oct. 2022 (low water stage); while other sites, from the valley left side, had previously been sampled on 26 March 2023 (high water conditions) and on 26 November 2022 (low water stage) (Tables 1 and 2 ). Note that VAR spring could be sampled only during low water periods, since during high water, its outlet was flooded by the Sohodol streamflow. The water samples to be analysed for major, minor and trace elements were collected in Nalgene HDPE bottles. The analytical determinations on water samples filtered by Thermo Scientific Chromacol Polyether Sulphone Syringe Filters (0.45 µm pore size) were conducted in the Hydrogeochemistry Laboratory of the Emil Racoviţă Institute of Speleology (Bucharest, Romania). Gran electrometric titration with a HCl solution of 0.05 M concentration was used (Rounds 2006) for determining the total alkalinity. An UV/VIS double beam Lambda 25 spectrophotometer (PerkinElmer, United States) was used for measuring SO 4 concentrations according to the ASTM-D516-07 (American Society for Testing and Materials 1995) standard method. The determinations accuracy was measured by means of a SANGAMON-03 (Environment, Canada) certified reference. Table 2 Chemical characteristics of the sampled waters in Sohodol valley karst area Side of Sohodol Sampling site Sampling date pH conductivity Na K Ca Mg HCO 3 SO4 Cl NO 3 SiO 2 Fe Sr Al Ba As Rb µS/cm mg/L µg/L right FUS 14-Oct-2023 6.31 146.1 1.757 0.806 27.0 2.17 65.6 11.20 5.21 0.898 9.39 9.0 44.2 bql 6.40 1.349 1.014 CFUS 14-Oct-2023 5.81 152.2 1.731 0.754 27.0 2.21 80.0 11.14 bql 1.101 9.36 36.9 43.3 bql 6.24 1.373 0.951 PIC 15-Oct-2023 6.12 212.0 1.446 0.475 39.4 2.64 121.9 8.98 bql 1.488 8.18 28.0 34.7 8.46 5.73 1.332 0.618 PAT 15-Oct-2023 5.78 210.2 1.417 0.545 43.5 2.55 122.2 8.24 bql 1.425 7.90 23.7 33.6 9.04 5.52 1.295 0.584 PIV 14-Oct-2023 6.78 334.5 0.279 0.120 59.1 8.26 223.2 4.82 bql 1.051 2.43 58.7 24.2 13.95 4.74 1.142 bql FUS 7-May-2023 5.75 115.6 1.807 0.804 22.6 1.92 61.9 11.89 bql 1.189 9.44 34.9 36.7 20.77 4.77 0.547 1.021 PIC 7-May-2023 5.93 194.9 1.329 0.482 40.0 2.52 118.8 7.32 bql 2.082 7.24 63.2 26.1 27.75 5.18 0.238 0.630 PIV 6-May-2023 6.45 306.5 0.307 0.358 58.2 7.51 198.8 3.27 bql 1.153 1.71 71.5 19.2 7.43 6.37 bql 0.300 FUS 29-Oct-2022 6.08 144.2 1.880 0.918 26.6 2.21 71.9 9.95 1.19 bql 9.58 40.0 47.6 6.49 bql 0.503 0.955 CFUS 29-Oct-2022 6.09 159.5 1.845 0.914 29.0 2.32 100.8 9.57 bql 1.261 9.15 44.3 46.4 bql bql 0.484 0.911 PIC 29-Oct-2022 6.20 209.9 1.516 0.644 40.2 2.66 120.1 6.56 bql 1.737 8.13 77.7 35.6 7.46 bql 0.326 0.657 PAT 29-Oct-2022 5.99 209.5 1.504 0.630 41.6 2.63 123.6 5.06 bql 1.709 8.01 77.3 35.9 10.13 bql 0.345 0.626 left CVAR 15-Oct-2023 6.20 268.6 0.830 0.260 58.6 1.91 167.9 9.58 bql 1.595 5.67 42.0 39.8 6.87 14.78 0.942 bql VAR 15-Oct-2023 5.89 353.7 0.677 0.288 78.9 2.03 220.3 8.64 bql 2.030 5.07 60.9 46.0 bql 11.40 1.138 bql TRAP 15-Oct-2023 6.34 286.7 0.295 0.146 75.7 1.16 212.6 9.24 bql 1.086 3.73 60.6 26.8 bql 6.05 1.256 bql CVAR 26-Mar-2023 6.24 261.0 0.815 0.333 53.9 1.76 153.1 9.72 0.58 1.679 4.69 52.2 31.4 bql 10.42 bdl bql TRAP 26-Mar-2023 6.39 359.1 0.309 0.328 77.4 1.23 223.1 8.77 bql 1.690 3.10 84.4 24.6 bql 4.05 bdl 0.233 CVAR 26-Nov-2022 6.29 255.4 0.936 0.470 58.3 1.87 166.9 7.06 bql 2.028 6.07 121.3 40.3 13.54 9.68 0.116 bql VAR 26-Nov-2022 6.17 324.7 0.755 0.455 74.4 1.98 216.8 7.97 bql 2.626 5.44 156.3 46.5 bql 7.76 0.131 bql Relative analytical uncertainty (%) 5.0 5.0 7.6 9.3 6.5 5.0 10.0 10.0 5.8 10.0 9.3 6.7 3.4 11.6 9.8 10.3 13.6 bql – below quantification limit bdl – below detection limit For measuring the concentrations of all other chemical constituents there was used a NexION 300S (PerkinElemer, Shelton, CT, USA) ICP-MS system, provided with an S10 Autosampler. The determinations have followed the U.S. EPA (2014) 6020B standards. Determinations of Ca were conducted in dynamic reaction cell (DRC) mode, by using NH 3 as a reactive gas. The concentrations of Na, K, Mg and Sr were measured in kinetic energy discrimination (KED) mode by using He as inert gas. The chloride concentration determinations followed the standard mode (U.S. EPA 2014). Reference materials purchased from High-Purity Standards™ (Charleston, SC, USA) were used for calibrations. The contents of Na, K, Mg, Ca and Sr for the laboratory control samples were measured by using NIST Standard Reference Material®1640a, and the Cl contents for analogous samples were measured by using Simulated Seawater Standard (HighPS). The instructions of the ISO 11352:2012 standard were followed for estimating the analytical measurements uncertainty. Results and discussions Main geochemical features of the water samples As indicated by the Piper diagram (Fig. 2 a), a Ca–HCO 3 facies is characteristic to water samples collected from all considered sites, not only from impenetrable karst springs or from streams intercepted by caves, but also from FUS swallet. That swallet displays however a slight relative enrichment in SO 4 and Na, presumably as a consequence of the metamorphic and magmatic terrains which prevalently build up its catchment. In particular, the SO 4 enrichment could originate – similarly to the situations discussed by Ulloa-Cedamanos et al. (2020) – in the oxydation of small pyrite impurities that possiby occurred within the crystalline formations of the concerned watershed. At the same time, it appears that along the inferred underground flowpaths (starting from FUS swallet toward the inferred outflows PIC and PAT), the SO 4 and Na signatures become gradually less definite, to the detriment of the overall Ca–HCO 3 character. In order to better illustrate this trend, an additional representation was devised for the cations and anions ternary plots of the standard Piper diagram, by multiplying the concentrations of Na, K, Cl, SO 4 and NO 3 by a factor of 10 (Fig. 2 b). It is reasonable to assume that the water fraction which prevails in FUS swallet is that derived from silicate weathering. At the same time, the relative contribution of this silicate-derived water is expected to diminish progressively along the underground flowpaths toward the karst springs, because of additional inflows of carbonate water originating in the hosting limestone body. Such a space-variable balance between the silicate-derived and carbonate-derived water contributions could be the cause of the two trends outlined by the Piper diagram for the sampling sites on the right side of Sohodol valley (Fig. 2 b): (i) the alkali-earth involvement increases from FUS swallet, toward CFUS cave stream, an further toward the inferred outflows PIC and PAT, to the detriment of the alkali contribution; (ii) the alkalinity also increases from the swallet toward the outflows, to the detriment of the sulphate ion contribution. Analogous variations, although less conspicuous, are also visible starting from CVAR cave stream toward VAR spring, both of which are situated on the left side of Sohodol valley. Mixing patterns between allogenic and autogenic water inputs There was next attempted to identify natural tracers that could provide additional information on (i) underground hydrological connections within the karst region and (ii) the relative contributions of allogenic and autogenic inputs along the corresponding flowpaths. The most straightforward diagnoses in this respect should be provided by linear correlations between the concentrations of pairs of solutes that behaved conservatively. Such patterns displayed by bivariate plots indicate that two end-members of constant concentrations mix with one another in various ratios, which eventually determine the particular concentration values recorded at each sampled site. Given the existing karst setting, the two involved end-members are expected to be allogenic (silicate-derived) and autogenic (carbonate-derived) water. For the considered karst region, the tightest linear correlations between samples simultaneously collected from various locations were obtained for Na, SiO 2 , and Ba (Figs. 3 and 4 ). The most eloquent in terms of karst catchments delineation appeared to be two diagrams: one in which Ba concentrations were plotted against the concentrations of SiO 2 (Fig. 3 a), and the other in which Ba was plotted against Na (Fig. 3 b). In each of the two plots, mixing lines fitted to data points that corresponded to simultaneously collected samples clearly belong to two distinct sets: one set includes only the sampling sites located on the right side of Sohodol valley (filled symbols), while the other set includes only the sampling points from the valley left side (empty symbols). All samples assumed to be proxies of the autogenic (pristine carbonate) end-member plot in a narrow domain with small concentrations of SiO 2 (1.5 ÷ 4.0 mg/L) and Na (~ 0.3 mg/l), despite the fact that PIV sampling site is located on the right side of Sohodol valley, whereas TRAP is situated on the valley left side. Implicitly, the largest contributions of SiO 2 and Na must be provided by the allogenic end-members. One remarkable feature outlined by Fig. 3 is that the Ba/SiO 2 and Ba/Na concentration ratios in the allogenic end-member inferred to contribute to the left side sampling sites (CVAR and VAR) are significantly larger than the corresponding ratios of the allogenic end-member involved in the supply of the right side sampling points (FUS, CFUS, PIC ad PAT). It is accordingly suggested that: (i) on each side of the valley, distinct karst catchments developed, and (ii) significant differences exist in terms of Ba/SiO 2 and Ba/Na ratios between the allogenic inputs contributing to each of the two catchments. As a first order approach, the allogenic (silicate-derived) end-member that supplies the right side sampling points can be considered the water of FUS swallet (whose watershed contains relatively few carbonate terrains, Fig. 1 ). On each mixing line that includes samples simultaneously collected from the right-side sampling sites (Fig. 3 ), the data points associated to CFUS cave stream and to PIC and PAT major outflows fall in-between the conjectured allogenic (silicate) and autogenic (carbonate) end-members FUS and PIV, respectively. It is thus suggested that FUS, CFUS, PIC and PAT sampling sites are indeed hydrologically connected (as formerly asserted by Iurkiewicz and Mangin, 1994), and that the cave stream CFUS, as well as each of the major karst outflows PIC and PAT, consist of allogenic-autogenic water mixtures. The relative input of silicate (allogenic) fraction in those mixtures progressively decreases along the conjectured underground flowpath which extends from FUS swallet to CFUS cave stream, then further to PIC and PAT major springs: such an evolution pattern is outlined by the gradually diminishing SiO 2 and Na concentrations (Fig. 3 ). In the case of the left side sampling sites (empty symbols in Fig. 3 ), a similar reduction of the silicate water contribution is suggested to occur between CVAR cave stream and VAR impenetrable spring. However, since both sampling sites are water outflows, their likely interconnection does not necessarily consist of CVAR cave stream directly supplying VAR spring; but rather that a common allogenic (silicate-derived) input reaches both water flows, where it mixes with autogenic (carbonate-derived) diffuse recharge, whose contribution is more abundant in VAR than in CVAR sampling site. Implicitly, a silicate-derived (allogenic) end-member is conjectured to exist, which has SiO 2 , Na and Ba contents larger than those of CVAR cave stream; so far however, the contributing inflow representing that allogenic end-member has not been identified. The Na vs. SiO 2 bivariate plot (Fig. 4 ) is the one which outlines the tightest linear correlations between data points that correspond to simultaneously collected samples. The fitted linear regressions have considered sampling sites on the right side of Sohodol valley, separately from sampling sites on the valley left side, taking into consideration the corresponding distinction revealed by the previously discussed Ba vs. SiO 2 and Ba vs. Na diagrams. Yet as far as Na vs. SiO 2 mixing lines are concerned, only little difference seems to exist between the right and left side sampling sites. This circumstance seems to indicate that not only the carbonate (autogenic) end-member proxies have similar Na/SiO 2 concentration ratios, but also the allogenic (silicate-derived) end-members. Therefore, by using just the Na vs. SiO 2 reciprocal concentration plot, it would have been virtually impossible to identify the distinction existing between the karst catchments of the right and the left sides of Sohodol valley. At the same time, if the separation between the right and left sides of the valley is taken beforehand into account, it is obvious that the data points relative positions within the Na vs. SiO 2 diagram are fully consistent with the hydrological connections and the relative contributions of allogenic and autogenic inputs which had been conjectured based on the Ba vs. SiO 2 and Ba vs. Na bivariate plots. It is also worth mentioning that in all three diagrams (Ba vs. SiO 2 – Fig. 3 a, Ba vs. Na – Fig. 3 b, and Na vs. SiO 2 – Fig. 4 ), the data-points corresponding to samples simultaneously collected from the PIC and PAT outflows are virtually coincident. This result is consistent with the tracer test results reported in Iurkiewicz and Mangin (1994), which indicated that those two major springs are ”twin” outflows of a single karst drainage system. Quantifying relative contributions of allogenic (silicate-derived) and autogenic (carbonate-derived) water As previously discussed, the linear trends outlined in the Ba vs. SiO 2 , Ba vs. Na and Na vs. SiO 2 diagrams (Figs. 3 a, 3 b and 4 , respectively) indicate that the corresponding solutes concentrations are controlled by binary mixing between silicate (allogenic) and carbonate (autogenic) end-members. The contribution that each of those two end-members has in a particular water sample can be assessed, similarly to the approach of Katz et al. (1998), Qin et al. (2017), or Gill et al. (2018), by a two-component mixing model. Specifically, the allogenic end-member fraction f all in the sampled mixture is expressed as: f all = ( C m - C aut )/( C all - C aut ) (1) where C m, C all , and C aut are the concerned solute concentrations in the mixture, the allogenic end-member, and the autogenic end-member, respectively. Taking into account that the major karst springs PIC and PAT had been shown to discharge mixtures of allogenic and autogenic water, the allogenic end-member fraction which contributed to each of those two outflows could be computed by means of Eq. (1). The concentration of PIV small spring was adopted as autogenic end-member, and the FUS swallet concentration as allogenic end-member. The computations were conducted for two distinct sampling dates, October 2023 and May 2023; and for each of those sampling operations, separate estimations were performed by using each of the three distinct tracers: SiO 2 , Na and Ba. The obtained values are listed in Table 3 . Table 3 Allogenic water fractions in the karst springs PAT (the Oct 2023 sampling) and PIC (the Oct 2023 and May 2023 samplings). For each instance, there are indicated the fractions separately computed by means of each of the tracers SiO 2 , Na and Ba Sampling site PAT PIC Sampling date Oct 2023 Oct 2023 May 2023 Tracer SiO 2 0.79 0.83 0.72 Na 0.77 0.79 0.68 Ba 0.47 0.59 0.74 In May 2023, allogenic water fractions could be computed only for PIC spring (since PAT spring was not sampled at that date). Quite consistent allogenic water fraction values (around 0.7) were obtained by means of each considered tracer (SiO 2 , Na and Ba). The allogenic fraction values obtained for the same spring in October 2023 by using either SiO 2 , or Na as a tracer, were consistent with each other and larger (around 0.8) than the values obtained in May 2023. The value (0.59) based on Ba concentrations appeared however to be less accurate. For the October 2023 sampling of PAT spring, computations based on SiO 2 also provided similar fractions with the computations based on Na (slightly smaller than 0.8, on the average); whereas the value based on Ba concentrations appeared to be less reliable (0.47). There can be concluded that PAT spring included a slightly smaller fraction of allogenic water than the sample simultaneously collected from PIC spring. In more general terms, the allogenic fraction in PIC outflow during the high water stage (May 2023) resulted to be smaller than during the low water period (October 2023). It is implicitly suggested that on the occasion of flood episodes, autogenic recharge increases, on the whole, at a faster rate than the allogenic one. Such a general conclusion appears to be largely consistent with more detailed results provided by Lorette et al. (2021) for a flood episode recorded in a karst region of southern France. Possible controls on the Ba abundance of the allogenic water inputs A distinctive feature of Sohodol karst region consists in the significantly smaller Ba/SiO 2 and Ba/Na ratios displayed (Fig. 3 ) by the allogenic supply to the valley right side sampling sites (i.e. the FUS swallet), as compared to the analogous ratios recorded in the case of the left side allogenic input (the one which supplies CVAR and VAR). Such a setting suggests that also the rock formations leached by the corresponding allogenic water flows could considerably differ from each other in terms of their Ba/SiO 2 and Ba/Na ratios. In an attempt to substantiate such a hypothesis about water-rock interactions in the considered watersheds, two additional plots have been constructed with data provided by whole rock chemical analyses: Ba/SiO 2 vs. Ba (Fig. 5 a) and Ba/Na vs. Ba (Fig. 5 b). For devising the diagrams, since most of the Sohodol watershed is developed on Lainici-Păiuş rock formations, within which three types of magmatic intrusions had been identified, use has been made of the whole rock chemical composition data presently available for those intrusions: namely, the analyses provided by Savu et al. (1974) for leucogranitoid dykes and sills collected from the Jiu and Şuşiţa valleys, those provided by Savu et al. (1971) for granites collected from the Suseni pluton (located immediately to the east of Sohodol watershed), and those provided by Féménias et al. (2008) for Motru Dyke Swarm andesites and basaltic andesites (collected from the areas designated as Jiu Susita and North Bistrita). Unfortunately, no similar chemical analyses are also available for any of the Lainici-Păiuş metamorphic rocks. Figures 5 a,b indicates that leucogranitoids, together with the Suseni pluton granites, form a distinct group of Ba-rich rocks. Consequently, prevalent leaching of such lithologies might explain the Ba-enrichment displayed by the allogenic input conjectured to supply the karst water sampling sites VAR and CVAR located on the left side of Sohodol valley. Alternatively, Ba contents of the Motru Dyke Swarm rocks are significantly smaller (by one order of magnitude in some cases) than those of the granites in Suseni pluton, or of the leucogranitoids. Therefore, the Ba-poor water of FUS swallet may indicate that in the corresponding sinking stream watershed, dykes of Motru Swarm type are abundant. Based on the previously mentioned rock samples analyses, a Na/SiO 2 vs. Ba bivariate plot has also been constructed (Fig. 5 c). It clearly shows that for the considered rock formations, the Na/SiO 2 ratios variation range is much narrower than the variation range of either the Ba/SiO 2 (Fig. 5 a), or the Ba/Na (Fig. 5 b) ratios. In fact, the Ba contents of the rock samples are clearly uncorrelated with the corresponding Na/SiO 2 ratios, and those ratios only slightly vary between one lithological type and another. The latter observations could explain why all allogenic end-members involved in the supply of the sampled karst waters did not differ significantly from each other in terms of their Na/SiO 2 ratios, irrespective of the catchment to which the sampling points belonged (Fig. 4 ). All in all however, more elaborate interpretations on the water-rock interaction topic are not warranted, due to the paucity of rock chemistry data available for the considered region, and especially because of the complete absence of such information pertaining to the metamorphic formations. One further point to be emphasized is that on most water sampling occasions, all three considered natural tracers, Na, SiO 2 , and Ba were more concentrated in the allogenic (silicate-derived) water input than in the autogenic (carbonate) one (Figs. 3 , 4 ). On a single instance however (the samples collected in May 2023 from the right side of Sohodol valley), the concentrations of Ba in the autogenic end-member exceeded the corresponding concentrations of the allogenic end-member. The particular behaviour recorded on that high water period could be the result of an even larger fraction of Ba-poor silicate rocks being temporarily involved in providing allogenic recharge to FUS swallet. Still one cannot exclude an alternative explanation, that would consider disturbances associated to the intense seismic activity (Radulian et al. 2023) which has affected the considered area for a few months, starting with February 2023. Comparison with previously reported Ba vs. Na concentration relationships in karst aquifers with allogenic recharge In terms of Ba and Na behaviour, the closest analogue reported so far for the Sohodol valley sampling sites appears to be the Hérault stream watershed, in southern France: there, simultaneous enrichments in Na and Ba were displayed by silicate-derived sinking streams, while the correspondingly connected karst outflows were noticed to be depleted in both elements (Petelet at al. 1998). For two karst springs sampled by Moldovan et al. (2021) in the South Carpathians (Romania) and designated as GWR1 and GWR3, Török et al. (2023) have conjectured that they likely included a silicate-derived (hence allogenic) water contribution, and that their content of dissolved Na and Ba originated mainly in carbonate rocks weathering. The latter inference could suggest that the concerned outflows were analogues of the PIV and TRAP springs, which had been shown in the present study to discharge only pristine carbonate water. A similarity with springs like PIV and TRAP would however be at odds with the silicate water contribution inferred by Török et al. (2023) for the GWR1 and GWR3 outflows; on the other hand, an allogenic input would explain the GWR1 and GWR3 springs enrichment in Ba and Na (with concentrations that significantly exceeded, in most instances – Fig. 6 - those of PIV and TRAP springs of Sohodol watershed). One cannot therefore exclude the possibility that although small amounts of Ba and Na dissolved in the springs addressed by Moldovan et al. (2021) and Török et al. (2023) were derived from carbonate rocks dissolution, larger amounts actually originated in allogenic (silicate-derived) water contributions. In the case of Gort Lowlands karst network (western Ireland), aqueous concentrations of Ba and Na reported by Gill et al. (2018) proved to be linearly correlated (Fig. 7 ), outlining binary mixing between allogenic and autogenic water inputs. Similarly to the Sohodol valley setting, the allogenic end-member is a sinking stream, while the autogenic end-member proxy is a particular karst spring. However, no cave streams have been sampled in that case, but instead, samples were collected from water surcharging out of the conduit network: on the mixing line, the latter samples plot – similarly to cave stream samples of Sohodol valley – between the swallet and the karst catchment main outflow. It is thus indicated that the allogenic water relative contribution gradually diminishes along the underground flowpaths, to the benefit of the autogenic inputs contribution. Notice that Gort Lowlands is, to the best of our knowledge, the only karst setting reported so far where Na is more abundant in the autogenic end-member than in the allogenic one (Fig. 7 ). This specificity (which appears to mirror the impact of the nearby seawater - Gill et al. 2018) did not alter however the binary mixing pattern which indicates that along the undergound flowpaths, the autogenic water contribution progressively increases to the detriment of the allogenic input contribution. Conclusions The trace element Ba, in conjunction with the major constituents SiO 2 and Na, have been used as natural tracers for investigating underground drainage patterns in karst catchments which are located in the Sohodol valley and are subject to allogenic (silicate-derived) recharge. Advantage was taken of the fact that various silicate rocks included in the watersheds that supplied allogenic water to the considered karst aquifers did not significantly differ from each other in terms of either Na, or SiO 2 contents; instead, Ba contents differed by up to one order of magnitude between one type of silicate rock and another. As a result, it was possible to distinguish a karst catchment supplied by Ba-rich allogenic inputs, from another karst catchment supplied by Ba-poor allogenic water; however, such a distinction could not have been outlined by using only the sampled waters concentrations of SiO 2 and Na. While most previous studies concerned with allogenic and autogenic inputs in karst aquifers had addressed only surface rivers and karst springs, the present investigation has focused on particular underground flowpaths which connected a swallet to a cave stream, and further to the final karst outflows. For each of the three natural tracers which had been considered (Na, SiO 2 and Ba), the concentrations distribution consistently outlined a gradual reduction of the allogenic recharge relative contribution, to the benefit of the relative contribution of the autogenic (carbonate) water inputs: from a swallet to a cave stream, and further from cave streams to the final karst outflows (for which the included fraction of allogenic water always remained important, about 70–80%, with the larger percentage being recorded during a low water stage). These results further support the reliability of the considered natural tracers for estimating the relative contributions of allogenic and autogenic inputs in karst waters. A synopsis of the considered natural tracers ability to elucidate underground drainage patterns in the Sohodol valley karst area is provided in Fig. 8 , which shows that: (i) all three considered solutes (Na, SiO 2 and Ba) behave in the considered setting conservatively; (ii) the outlined binary mixing patterns indicate that from a surface stream swallet toward a cave stream, and further from cave streams toward karst outflows, the autogenic water relative contribution gradually increases, to the detriment of the relative contribution of allogenic inputs; (iii) in a reciprocal concentration plot including Ba, two karst catchments can be clearly distinguished from each other, whereas in an analogous SiO 2 vs. Na diagram, such a distinction is virtually undetectable. Both in Romania and worldwide, fluviokarst environments with allogenic recharge characteristics similar to those encountered in Sohodol valley are not uncommon. In such settings, the utilization of the three considered natural tracers - Ba in conjunction with SiO 2 and Na - could be further tested for investigating underground drainage patterns within the corresponding karst catchments. Declarations Conflict of interest The authors have no relevant financial or non-financial interests to disclose. Funding The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Author Contribution Conceptualization, HM, NC, MV, CN and GC; methodology, NC, HM, CM, MV, CN, GC, AT and LN; formal analysis, NC, HM, CM, GC, AT, LN and MV; investigation, NC, HM, GC, and MV; writing – original draft preparation, HM, NC, MV, and LN; writing – review and editing HM, NC and MV. All authors have read and agreed to the published version of the manuscript. 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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-4317845","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":297518914,"identity":"5b969f08-a0ef-41b5-bace-37f576f49277","order_by":0,"name":"Nicolae Cruceru","email":"","orcid":"","institution":"\"Emil Racoviță\" Institute of Speleology, Romanian Academy","correspondingAuthor":false,"prefix":"","firstName":"Nicolae","middleName":"","lastName":"Cruceru","suffix":""},{"id":297518915,"identity":"ca8ccd85-71d5-431b-9047-6685eae126bb","order_by":1,"name":"Horia Mitrofan","email":"","orcid":"","institution":"“Sabba S. Ştefănescu” Institute of Geodynamics, Romanian Academy, Bucharest, Romania","correspondingAuthor":false,"prefix":"","firstName":"Horia","middleName":"","lastName":"Mitrofan","suffix":""},{"id":297518916,"identity":"401cbe7c-511d-4a4c-9646-d192c745532a","order_by":2,"name":"Constantin Marin","email":"","orcid":"","institution":"\"Emil Racoviță\" Institute of Speleology, Romanian Academy","correspondingAuthor":false,"prefix":"","firstName":"Constantin","middleName":"","lastName":"Marin","suffix":""},{"id":297518917,"identity":"efdac564-bb9b-4599-9945-7eb38d84a574","order_by":3,"name":"Marius Vlaicu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA30lEQVRIiWNgGAWjYJCCAyCCj4GxgYGhQoIELWxgLWeI1MIA0QIEjG1EqNRtP/vwMM8fhsQ29sONn3nnWdjzSx9g+/ABjxazM+kGh3nbgFp4EpulebdJJM7sS2CeOQOflgNpDId5GxiM2YC6mIFaEgzOMDAz8+DTcv4ZA8hhxmz8D4Fa5kjY2xPUcgNoCw8bgxybBMiWBgnGDTwEtTxjODi3TQKo5WGz5JxjEokzzjA2M+L1y/k05g9v/tjw8POnP/zwpqbOnr+H+TADvhCDApQYBMXpKBgFo2AUjAKKAABwbUEsqUklNQAAAABJRU5ErkJggg==","orcid":"","institution":"\"Emil Racoviță\" Institute of Speleology, Romanian Academy","correspondingAuthor":true,"prefix":"","firstName":"Marius","middleName":"","lastName":"Vlaicu","suffix":""},{"id":297518918,"identity":"748240d4-6601-46ed-adbe-b4737a9d6c41","order_by":4,"name":"Cornel Naidin","email":"","orcid":"","institution":"Clubul de speologie Silex","correspondingAuthor":false,"prefix":"","firstName":"Cornel","middleName":"","lastName":"Naidin","suffix":""},{"id":297518919,"identity":"1b873189-888e-4d51-a3d0-b2cadb0782d7","order_by":5,"name":"Gabriel Constantinescu","email":"","orcid":"","institution":"","correspondingAuthor":false,"prefix":"","firstName":"Gabriel","middleName":"","lastName":"Constantinescu","suffix":""},{"id":297518920,"identity":"796a5337-0597-4384-ba49-a2fa9e630b99","order_by":6,"name":"Alin Tudorache","email":"","orcid":"","institution":"\"Emil Racoviță\" Institute of Speleology, Romanian Academy","correspondingAuthor":false,"prefix":"","firstName":"Alin","middleName":"","lastName":"Tudorache","suffix":""},{"id":297518921,"identity":"503bd301-a928-4698-80d8-93667c58ace2","order_by":7,"name":"Lucica Niculae","email":"","orcid":"","institution":"“Sabba S. Ştefănescu” Institute of Geodynamics, Romanian Academy, Bucharest, Romania","correspondingAuthor":false,"prefix":"","firstName":"Lucica","middleName":"","lastName":"Niculae","suffix":""}],"badges":[],"createdAt":"2024-04-24 11:26:26","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4317845/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4317845/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12665-024-11990-8","type":"published","date":"2024-11-28T15:56:50+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":55719853,"identity":"f7602a7b-b85a-4daf-bc1b-9fb570b41d51","added_by":"auto","created_at":"2024-05-02 08:38:17","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1711494,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Map of the investigated area encompassed by the Sohodol catchment water divide. There are indicated the main geological features (after Stan et al. 1979, simplified), the sampled karst water flows, and the extent of the sub-catchment supplying FUS swallet; (b) Detail of the region included in the brown dashed rectangle in (a); (c) Index map showing the position of Sohodol catchment within Romania\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/4786f11495b4232a295db88b.png"},{"id":55719869,"identity":"84ccd5a8-b553-4ce7-8815-474a5a0c4094","added_by":"auto","created_at":"2024-05-02 08:38:17","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":699735,"visible":true,"origin":"","legend":"\u003cp\u003ePiper diagram of the sampled waters. (a) Standard representation; (b) Additional representation of the Piper diagram cation and anion ternary plots, in which the concentrations of Na, K, Cl, NO\u003csub\u003e3\u003c/sub\u003e and SO\u003csub\u003e4\u003c/sub\u003e were multiplied by a factor of 10, in order to improve the readability. Filled symbols indicate samples collected from the right side of Sohodol valley, while empty symbols indicate samples collected from the valley left side: warm to cold tones indicate transition from a swallet (with prevalently silicate water contribution) toward springs that discharge assumedly pristine carbonate water\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/6169250b176f4be9e18801ff.png"},{"id":55719873,"identity":"daed310b-503b-4256-af33-9584b3129986","added_by":"auto","created_at":"2024-05-02 08:38:18","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":516311,"visible":true,"origin":"","legend":"\u003cp\u003eBa vs. SiO\u003csub\u003e2\u003c/sub\u003e (a) and Ba vs. Na (b) bivariate plots of the sampled waters. Full and empty symbols are for sampling sites on the right and left sides of Sohodol valley, respectively. The dashed regression lines were fitted to data points associated to samples simultaneously collected either from the right, or and from the left side of the valley. Such lines outline binary mixing trends between allogenic (SiO\u003csub\u003e2\u003c/sub\u003e- and Na-rich) and autogenic (SiO\u003csub\u003e2\u003c/sub\u003e- and Na-poor) water inputs\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/d967257ed2c90578617ce536.png"},{"id":55719875,"identity":"0184f929-9611-4194-9275-14433d51f624","added_by":"auto","created_at":"2024-05-02 08:38:19","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":568867,"visible":true,"origin":"","legend":"\u003cp\u003eNa vs. SiO\u003csub\u003e2\u003c/sub\u003e bivariate plot of the sampled waters. Full and empty symbols are for sampling sites on the right and left sides of Sohodol valley, respectively. The dashed regression lines were fitted to data points associated to samples simultaneously collected either from the right, or and from the left side of the valley. Such lines outline binary mixing trends between allogenic (SiO\u003csub\u003e2\u003c/sub\u003e- and Na-rich) and autogenic (SiO\u003csub\u003e2\u003c/sub\u003e- and Na-poor) water inputs\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/957af96a6302c759a41f8078.png"},{"id":55719870,"identity":"4672627c-7879-4c93-b743-050cfee6eb61","added_by":"auto","created_at":"2024-05-02 08:38:17","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":337031,"visible":true,"origin":"","legend":"\u003cp\u003eBa/SiO\u003csub\u003e2\u003c/sub\u003e vs. Ba (a), Ba/Na vs. Ba (b), and Na/SiO\u003csub\u003e2\u003c/sub\u003e vs. Ba (c) bivariate plots constructed for rock samples which might be representative for the formations weathered by the allogenic inputs to the sampled karst waters. The whole rock chemical data were retrieved from Savu et al. (1974) for leucogranitoid dykes, from Savu et al. (1971) for granites of Suseni pluton, and from Féménias et al. (2008) for andesites and basaltic andesites of the Motru Dyke Swarm.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/5252feb621c9aaf998143474.png"},{"id":55719871,"identity":"c01238a3-3391-4e10-a66d-7b7552b68ce3","added_by":"auto","created_at":"2024-05-02 08:38:17","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":489079,"visible":true,"origin":"","legend":"\u003cp\u003eBa vs. Na bivariate plot essentially similar to that in Fig. 3b, but additionally including water samples collected in various seasons (Moldovan et al. 2021;Török et al. 2023) from two other karst outflows (GWR1 and GWR3) situated also in the South Carpathians (Romania)\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/f442fd970fc8a8ea8db81b42.png"},{"id":55719872,"identity":"629456c5-2748-48e5-a787-64209ae64fc9","added_by":"auto","created_at":"2024-05-02 08:38:18","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":67800,"visible":true,"origin":"","legend":"\u003cp\u003eBa vs. Na bivariate plot constructed with data provided by Gill et al. (2018) for water samples simultaneously collected from various sites of the Gort Lowlands karst network (Ireland). In the legend, the original ID of each sample is indicated in brackets. The dashed regression line fitted to the data points outlines binary mixing between allogenic (Ba-rich and Na-poor) and autogenic (Ba-poor and Na-rich) water inputs\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/be29b653ee124e8f54b047f7.png"},{"id":55719874,"identity":"92502288-da53-4061-b95b-a4e4d2e5cb2a","added_by":"auto","created_at":"2024-05-02 08:38:18","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":466394,"visible":true,"origin":"","legend":"\u003cp\u003eBa vs. Na and SiO\u003csub\u003e2\u003c/sub\u003e vs. Na bivariate plots summarizing the considered natural tracers ability to elucidate underground drainage patterns in Sohodol valley. For clarity, the diagrams include only water samples collected on a single instance (October 2023)\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/a04913da2cab0187a3a553bd.png"},{"id":70381785,"identity":"17f8516e-ac3b-464b-b01f-c117e3ae5d06","added_by":"auto","created_at":"2024-12-02 16:14:46","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5533759,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4317845/v1/87410e2f-68ec-4013-813e-c8f141882bbb.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Dissolved Ba as discriminator between two adjacent karst catchments that are both subject to allogenic recharge (Sohodol valley, Vâlcan Mountains, Romania)","fulltext":[{"header":"Introduction","content":"\u003cp\u003eA basic type of karst landscape includes, as main features, valleys which had initially been shaped by surface streams. Subsequently, the corresponding river courses were captured in valley-bottom swallets, that conveyed the water flow to underground conduits developed by dissolution in a carbonate rocks substratum. Such a setting is designated (e.g., Smart 1988; Taylor and Greene 2008; Phillips 2017) as \u003cem\u003efluviokarst\u003c/em\u003e - in contrast to \u003cem\u003eholokarst\u003c/em\u003e, a landscape that essentially consists of closed depressions formed by dissolution, and which is virtually devoid of any stream channels.\u003c/p\u003e \u003cp\u003eFluviokarst is in many instances related (e.g., Jennings 1982; Bočić 2003; Bočić and Baćurin 2004; Anthony ad Granger 2007; Mihevc 2007; Herman et al. 2012) to stream catchments whose headwaters are incised in a non-carbonate substratum, while the downstream reaches develop within carbonate rocks (the latter formations being those which had favoured the stream piracy in the underground).\u003c/p\u003e \u003cp\u003eIn such multi-lithological settings, the karst groundwater chemical composition is largely controlled (e.g., Petelet et al. 1998; Qin et al. 2017; Gill et al. 2018; Lorette et al. 2021; Fern\u0026aacute;ndez‑Ortega et al., 2023) by mixing between two main inputs: (i) water associated to the weathering of non-carbonate (usually silicate) formations, and which provides allogenic recharge to the karst areas situated downgradient, and (ii) autogenic recharge water, which dissolves the carbonate rock bodies that host the actual underground karst flowpaths. In order to discriminate between those two contributing water types, in the present study there have been selected three natural inorganic chemical tracers: Na, SiO\u003csub\u003e2\u003c/sub\u003e and Ba.\u003c/p\u003e \u003cp\u003eProvided that no evaporite deposits or of anthropic pollution sources, Na was previously noticed to originate almost exclusively (e.g., Han and Liu 2004; Ma et al. 2011; Pu et al. 2012; Qin et al. 2017; Petalas and Moutsopoulos 2019) in silicate rocks weathering (dissolution of feldspars or other silicate minerals), while only a negligible amount of Na was released from limestone or dolomite dissolution. Therefore Na has been used on several occasions (Qin et al. 2017; Guo et al. 2019) for tracking water inflows from surface streams into karst aquifers.\u003c/p\u003e \u003cp\u003eIn contrast, SiO\u003csub\u003e2\u003c/sub\u003e has been only seldom considered as a possible natural tracer in karst environments with allogenic recharge. This circumstance is rather surprising, given that one would normally expect the dissolved SiO\u003csub\u003e2\u003c/sub\u003e content of silicate-derived (allogenic) water to be conspicuously larger than the content of the carbonate-derived (autogenic) inputs. Yet an example from the Upper Floridan aquifer (Katz et al. 1998) illustrates an opposite situation, in which a sinking river had a significantly lower SiO\u003csub\u003e2\u003c/sub\u003e concentration than pristine carbonate-derived groundwater which was sampled, under low flow conditions, from the karst aquifer. Another example of SiO\u003csub\u003e2\u003c/sub\u003e concentrations progressively increasing from the recharge toward the discharge zones was provided by Ma et al. (2011) for a karst aquifer in northern China. The dissolved silica enrichment has been ascribed in that case to higher temperatures acquired by water which before resurfacing in the discharge zone, had circulated along deep (up to 2 km) flowpaths. Other reports of silica abundances in karst waters (e.g., Lastennet and Mudry, 1997; D\u0026iacute;az-Puga et al. 2016; Denimal et al. 2017) have addressed settings virtually devoid of any allogenic recharge, hence the corresponding results cannot be directly compared to those of the present investigation.\u003c/p\u003e \u003cp\u003eLike in the case of SiO\u003csub\u003e2\u003c/sub\u003e, few reports exist so far (Molina-Porras et al. 2017; Gill et al. 2018; Petalas and Moutsopoulos 2019) concerning the utilization of the minor element Ba as natural tracer in karst environments with allogenic recharge. Yet in the area considered by the present study, Ba proved to be, out all analysed constituents, the only one being able to properly discriminate between two distinct karst catchments. Extended areas within the watersheds which provide allogenic recharge to those catchments are occupied by magmatic intrusions, whose chemical composition specificities (reported in Savu et al. 1971, 1974; F\u0026eacute;m\u0026eacute;nias et al. 2008) were taken into account in an attempt to explain the recorded particular behaviour of Ba.\u003c/p\u003e \u003cp\u003eIn the present investigation, advantage has also been taken of the conservative behaviour which had been previously outlined in karst environments for Na (Petelet at al. 1998; Qin et al. 2017; Gill et al. 2018), SiO\u003csub\u003e2\u003c/sub\u003e (Katz et al. 1998) and Ba (Molina-Porras et al. 2017; Gill et al. 2018). Consequently, those tracers\u0026rsquo; concentration values were used in the present study for constructing bivariate plots that provided information on:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003ebinary mixing patterns mirroring hydrological connections along underground flowpaths;\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003erelative contributions of the allogenic and autogenic inputs along those flowpaths.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eAn approach somehow similar to that of Gill et al. (2018) and Lorette et al. (2021) was adopted, by focusing on geochemical signatures associated to underground flowpaths along which the relative contribution of autogenic inputs (originating in diffuse infiltration through the limestone body) progressively increased, to the detriment of the allogenic water contribution: starting from swallets supplied by silicate rock watersheds, toward streams intercepted in underground conduits, and further to the final karst outflows.\u003c/p\u003e \u003cp\u003eEventually, consistent estimates of the allogenic water fraction discharged by the considered major karst outflows have been provided by the concentrations of Na and SiO\u003csub\u003e2\u003c/sub\u003e (and sometimes, also by the Ba contents).\u003c/p\u003e \u003cp\u003eOverall, the obtained results could represent initial assessments concerning the ability of the three considered natural tracers to elucidate underground drainage patterns within karst catchments subject to allogenic recharge.\u003c/p\u003e"},{"header":"Physiographic and geological setting","content":"\u003cp\u003eThe present study addresses a fluviokarst region in V\u0026acirc;lcan mountains (South Carpathians range), within the catchment of Sohodol valley (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). It is a rugged topography area, with several peaks ranging between 1400 and 1500 m a.s.l., while only one, Şigleul Mare, reaches almost 1700 m a.s.l.). On the other hand, the streambed of the Sohodol main valley descends, at its exit from the considered karst domain, down to 400 m a.s.l..\u003c/p\u003e \u003cp\u003eMost part of the considered catchment is covered by beech forests, grassland usually occupying only some of the highest peaks and ridges. The climate is temperate, with a mean annual temperature that declines from 8\u0026ndash;9\u0026deg;C at the mountain front, down to about 2\u0026deg;C on the highest ridges. Average annual rainfall amounts to about 900 mm at the mountain front, increasing to 1200\u0026ndash;1400 mm at higher altitudes. Two rainfall peaks occur, totalling 130\u0026ndash;150 rainfall days/year: the main peak is recorded during March-May, and the secondary one in November-December. Snow falls occur during the cold season, with the snow layer usually lasting for 100\u0026ndash;150 days (all indicated climate data are according to Muică 1995). Sudden temperature increases toward the end of February and in March result (Neamu 1998) in early snowmelt that triggers flash floods.\u003c/p\u003e \u003cp\u003eAll rock formations in the Sohodol watershed belong to a single geological unit, the Lainici Nappe (Berza et al. 1994; Li\u0026eacute;geois et al. 1996), whose basement includes two polymetamorphic groups (Berza 1978) of Late Precambrian age.\u003c/p\u003e \u003cp\u003eThe more recent, metasedimentary Lainici-Păiuş Group includes a lower \u0026ldquo;Carbonate-Graphitic Formation\u0026rdquo; underlying an upper \u0026ldquo;Quartzitic and Biotite Gneiss Formation\u0026rdquo; (Li\u0026eacute;geois et al. 1996). In addition, three types of magmatic intrusions were distinguished within the metamorphic formations: (i) dykes and bodies consisting of Late Precambrian leucogranitoids (Li\u0026eacute;geois et al. 1996); (ii) Late Precambrian granites and granodiorites building up large plutons (Savu et al., 1971; Berza, 1978); (iii) Early Paleozoic (Pre-Silurian) dykes and sills (\u0026ldquo;Motru Dyke Swarm\u0026rdquo;) which include mainly andesites and basaltic andesites (F\u0026eacute;m\u0026eacute;nias et al., 2008). Overall, two thirds of the Lainici-Păiuş Group occurrence area was estimated to be occupied by granitoids (Berza 1978), yet a thorough cartographic representation of this setting was provided only for the large Precambrian plutons (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe older, metavolcanic Drăgşan Group includes (Berza et al. 1994; Li\u0026eacute;geois et al. 1996) an Amphibolite Formation (consisting mainly of banded amphibolites). It is widely developed in the hanging wall of a major reverse fault that brings the amphibolites in contact with the Lainici-Păiuş Group (Stan et al. 1979; Berza et al. 1994). It has been however presumed (Berza, 1978) that Drăgşan metamorphics could be present also underneath the Lainici-Păiuş metasediments.\u003c/p\u003e \u003cp\u003eA Paleozoic cover common to both metamorphic groups includes (Stan et al., 1979) low grade formations consisting of chlorite and sericite schists (belonging to the Ordovician and Devonian time-interval), and of carbonate and graphitic rocks (of Carboniferous age).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe Mesozoic cover of the Lainici Nappe starts (Stan et al. 1979; Berza et al. 1994) with Early Jurassic siliciclastic deposits in Gresten facies (conglomerates, sandstones and shales). They are overlain by a thick carbonate series (various kinds of limestones, occasionally dolomitized \u0026ndash; Pop 1973) that was deposited during the Middle Jurassic-Early Cretaceous (Aptian) interval, and which hosts the karst features concerned by the present study. The carbonate series is transgressively covered by Middle-Late Cretaceous clastics, some of which are intruded by ophiolite veins and dykes (Stan et al. 1979). Locally, Middle Jurassic-Early Cretaceous carbonates also occur in a thrust sheet that tectonically overlies Middle-Late Cretaceous clastics.\u003c/p\u003e \u003cp\u003eThe watersheds at the headwaters of Sohodol trunk stream and of its main tributaries (Măcriş, Şipot, Gropu Sec, Scărişoara, Gropu cu Apă) are developed, over 72 km\u003csup\u003e2\u003c/sup\u003e, within terrains that include the Lainici Nappe metamorphic and granitic basement and its Paleozoic low-grade cover formations. The indicated stream courses next enter an extended surface occupied mainly by Mesozoic carbonate rocks, where the subsequent 42 km\u003csup\u003e2\u003c/sup\u003e of watersheds occur.\u003c/p\u003e \u003cp\u003eThe carbonate rocks domain is yet rendered more complex by of an uplifted, island-shaped granite body, which crops out over about 4 km\u003csup\u003e2\u003c/sup\u003e and accordingly imposes restricted pathways to the limestone-hosted underground flows along Sohodol valley (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e).\u003c/p\u003e\n\u003ch3\u003eSampling sites selection relying on previous information about karst hydrology\u003c/h3\u003e\n\u003cp\u003eKarst drainage features within the concerned section of Sohodol valley have been discussed in a paper published by Iurkiewicz and Mangin (1994). Based on their investigations, they conjectured that a common groundwater flow system was discharging via two large perennial karst springs, Pătrunsa (PAT) and Picuiel (PIC), both located on the right side of Sohodol valley (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). It was additionally stipulated that Fuşteica (FUS) impenetrable swallet - where Sohodol stream itself loses in its right-side bank part (and in drought periods, the entirety) of its discharge - contributed to the supply of the same groundwater flow network. Moreover, about 300 m downstream FUS swallet, and also on the right side of the valley, it is situated the Cave Downstream Fuşteica Swallet, whose fossil passages intercept, about 500 m after the entrance, an underground stream (sampling point CFUS - Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), which flows into a sump.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe sampling sites within the investigated karst area of Sohodol valley\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"13\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eside of Sohodol\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eType\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eName\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003ecode\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLatitude N\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eLongitude E\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eelevation (m a.s.l)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eestimated flow rate\u003csup\u003ea\u003c/sup\u003e (L/s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"5\" nameend=\"c13\" namest=\"c9\"\u003e \u003cp\u003esampling\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eOct 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003eMay 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003eMar 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003eNov 2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003eOct 2022\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"4\" rowspan=\"5\"\u003e \u003cp\u003eright\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eimpenetrable swallet\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFuşteica\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;12'29.29\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 7'54.96\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e516\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e250\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ecave intercepting an underground stream\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eDownstream Fuşteica Swallet\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCFUS\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;12'21.74\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 7'52.17\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e525\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003en.e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003emajor impenetrable spring with assumed allogenic supply\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePicuiel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePIC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;10'37.97\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 7'59.02\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e100\u0026ndash;200\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePătrunsa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePAT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;10'44.40\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 7'56.43\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e100\u0026ndash;500\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003esmall impenetrable spring with no allogenic input\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePiva\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003ePIV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;11'43.80\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 3'13.61\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e910\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e1\u0026ndash;10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eleft\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ecave intercepting an underground stream\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eAt the Mouth of Valea Rea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCVAR\u003csup\u003eb\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;10'22.82\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 8'10.81\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e415\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003en.e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eimpenetrable spring with assumed allogenic supply\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eValea Rea\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eVAR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;10'23.71\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 8'10.53\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e410\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003en.e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003esmall impenetrable spring with no allogenic input\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTravertine at Picuiel\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eTRAP\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e45\u0026deg;10'41.40\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e23\u0026deg; 7'59.90\"\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e430\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003en.e.\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003ex\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e\u0026nbsp;\u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e\u0026nbsp;\u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003csup\u003ea\u003c/sup\u003e - according to Iurkiewicz and Mangin (1994)\u003c/p\u003e \u003cp\u003e \u003csup\u003eb\u003c/sup\u003e - the indicated coordinates correspond to the cave entrance\u003c/p\u003e \u003cp\u003en.e. - not estimated\u003c/p\u003e \u003cp\u003eIurkiewicz and Mangin (1994) have published details of an artificial tracer test which had substantiated the interconnection between PIC and PAT springs, but no specific information was provided about tracer tests having checked if FUS swallet (and/or CFUS cave stream) were linked to PAT and PIC major outflows.\u003c/p\u003e \u003cp\u003eIn the framework of the present study, water samples have been collected from all the above-indicated sites located on the right side of Sohodol. There have been sampled in addition two sites situated on the valley left side (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e):\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eValea Rea (VAR) impenetrable perennial spring, which has a far less abundant flow rate than either PAT, or PIC outflows;\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003ethe underground stream intercepted in the Cave at the Mouth of Valea Rea, which is positioned quite close to VAR spring and about 5 m above it. A 40 m long streamlet (sampling point CVAR) permanently flows along the cave passage, to eventually discharge by the cave entrance.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e \u003cp\u003eIurkiewicz and Mangin (1994) have not dedicated any discussion to the latter two sites, and no artificial tracer test has addressed possible hydrological links that could involve VAR spring and/or CVAR cave stream.\u003c/p\u003e \u003cp\u003eIn an attempt to develop and expand the overall karst drainage model previously formulated by Iurkiewicz and Mangin (1994), the present study aimed to identify hydrochemical evidence that would contribute to elucidate underground hydrological connections which involved the six above-indicated sampling sites.\u003c/p\u003e \u003cp\u003eAt the same time, central to the present investigation was the circumstance that the relative contributions of the allogenic and autogenic water inputs differed between one sampling site and another. Specifically, since metamorphic and granitic formations built up most of the watershed supplying FUS swallet (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e), its sinking flow was considered to have a chemical composition largely representative for allogenic, silicate-derived water. Alternatively, it was reasonable o assume that each of the two springs PAT and PIC, and possibly also CFUS cave stream likely consisted of silicate-carbonate water mixtures. Moreover it was assumed, as a first order approach, that also VAR spring and CVAR cave stream discharged a mixture consisting of various proportions of silicate (allogenic) and carbonate (autogenic) water. Investigating the mixing process between allogenic and autogenic inputs also required some information on the chemistry of the pristine carbonate-derived (i.e. autogenic) water. Identifying sampling sites presumably representative in this respect was however not straightforward. One such site was conjectured to be the small perennial karst spring Piva (PIV), which discharged (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) from a limestone body isolated on a mountain top that was devoid of any allogenic water inputs. Since large amounts of travertine were noticed to have precipitated from PIV outflow, analogous deposits associated to another small perennial spring (TRAP), were assumed to indicate that also its water was exclusively carbonate-derived.\u003c/p\u003e \u003cp\u003eIt is still important to emphasize that in the case of TRAP spring, a hydrological connection with the other sampled sites is highly unlikely, while in the case of PIV spring, such a link is just impossible: those two small springs can therefore be viewed only as proxies of the carbonate-derived (autogenic) water which was assumed to be actually involved in the supply of PAT, PIC and VAR springs and of the CFUS and CVAR cave streams.\u003c/p\u003e\n\u003ch3\u003eSampling and analytical procedures\u003c/h3\u003e\n\u003cp\u003eA sampling operation including all the previously discussed sites (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e) has been conducted on 14\u0026ndash;15 October 2023, during a low water stage. Some of the concerned sites, located on the right side of Sohodol valley, had been sampled also on 6\u0026ndash;7 May 2023 (high water conditions) and on 29 Oct. 2022 (low water stage); while other sites, from the valley left side, had previously been sampled on 26 March 2023 (high water conditions) and on 26 November 2022 (low water stage) (Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and \u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e). Note that VAR spring could be sampled only during low water periods, since during high water, its outlet was flooded by the Sohodol streamflow.\u003c/p\u003e \u003cp\u003eThe water samples to be analysed for major, minor and trace elements were collected in Nalgene HDPE bottles. The analytical determinations on water samples filtered by Thermo Scientific Chromacol Polyether Sulphone Syringe Filters (0.45 \u0026micro;m pore size) were conducted in the Hydrogeochemistry Laboratory of the Emil Racoviţă Institute of Speleology (Bucharest, Romania).\u003c/p\u003e \u003cp\u003eGran electrometric titration with a HCl solution of 0.05 M concentration was used (Rounds 2006) for determining the total alkalinity. An UV/VIS double beam Lambda 25 spectrophotometer (PerkinElmer, United States) was used for measuring SO\u003csub\u003e4\u003c/sub\u003e concentrations according to the ASTM-D516-07 (American Society for Testing and Materials 1995) standard method. The determinations accuracy was measured by means of a SANGAMON-03 (Environment, Canada) certified reference.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eChemical characteristics of the sampled waters in Sohodol valley karst area\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"20\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c11\" colnum=\"11\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c12\" colnum=\"12\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c13\" colnum=\"13\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c14\" colnum=\"14\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c15\" colnum=\"15\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c16\" colnum=\"16\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c17\" colnum=\"17\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c18\" colnum=\"18\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c19\" colnum=\"19\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c20\" colnum=\"20\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSide of Sohodol\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSampling site\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSampling date\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003epH\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003econductivity\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eNa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eK\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMg\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003eHCO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c11\"\u003e \u003cp\u003eSO4\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c12\"\u003e \u003cp\u003eCl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c13\"\u003e \u003cp\u003eNO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c14\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c15\"\u003e \u003cp\u003eFe\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c16\"\u003e \u003cp\u003eSr\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c17\"\u003e \u003cp\u003eAl\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c18\"\u003e \u003cp\u003eBa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c19\"\u003e \u003cp\u003eAs\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c20\"\u003e \u003cp\u003eRb\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e\u0026micro;S/cm\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"9\" nameend=\"c14\" namest=\"c6\"\u003e \u003cp\u003emg/L\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c20\" namest=\"c15\"\u003e \u003cp\u003e\u0026micro;g/L\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"11\" rowspan=\"12\"\u003e \u003cp\u003eright\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eFUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14-Oct-2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e146.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.757\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.806\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e27.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e65.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e11.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e5.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e0.898\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e9.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e9.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e \u003cp\u003e44.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e6.40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e1.349\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e1.014\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eCFUS\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14-Oct-2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e152.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.731\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.754\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e27.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e80.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e11.14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.101\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e9.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e36.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e \u003cp\u003e43.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e6.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e1.373\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e0.951\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePIC\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15-Oct-2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e212.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.446\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.475\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e39.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e121.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e8.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.488\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e8.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e28.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e \u003cp\u003e34.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003e8.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e5.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e1.332\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e0.618\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePAT\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e15-Oct-2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e210.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e1.417\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.545\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e43.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e2.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e122.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e8.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.425\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e7.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e23.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e \u003cp\u003e33.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003e9.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e5.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e1.295\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e0.584\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003ePIV\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14-Oct-2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e334.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.279\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e59.1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e8.26\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e223.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e4.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e1.051\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e2.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e58.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e 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align=\"left\" colname=\"c16\"\u003e \u003cp\u003e40.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003e13.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e9.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e0.116\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eVAR\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e26-Nov-2022\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e6.17\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e324.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e0.755\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e0.455\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e74.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e1.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e216.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e7.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e2.626\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e5.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e156.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e \u003cp\u003e46.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e7.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e0.131\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003ebql\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"3\" nameend=\"c3\" namest=\"c1\"\u003e \u003cp\u003eRelative analytical uncertainty (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e7.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c8\"\u003e \u003cp\u003e6.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e5.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c10\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c11\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c12\"\u003e \u003cp\u003e5.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c13\"\u003e \u003cp\u003e10.0\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c14\"\u003e \u003cp\u003e9.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c15\"\u003e \u003cp\u003e6.7\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c16\"\u003e \u003cp\u003e3.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c17\"\u003e \u003cp\u003e11.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c18\"\u003e \u003cp\u003e9.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c19\"\u003e \u003cp\u003e10.3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c20\"\u003e \u003cp\u003e13.6\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003ebql \u0026ndash; below quantification limit\u003c/p\u003e \u003cp\u003ebdl \u0026ndash; below detection limit\u003c/p\u003e \u003cp\u003eFor measuring the concentrations of all other chemical constituents there was used a NexION 300S (PerkinElemer, Shelton, CT, USA) ICP-MS system, provided with an S10 Autosampler. The determinations have followed the U.S. EPA (2014) 6020B standards. Determinations of Ca were conducted in dynamic reaction cell (DRC) mode, by using NH\u003csub\u003e3\u003c/sub\u003e as a reactive gas. The concentrations of Na, K, Mg and Sr were measured in kinetic energy discrimination (KED) mode by using He as inert gas. The chloride concentration determinations followed the standard mode (U.S. EPA 2014). Reference materials purchased from High-Purity Standards\u0026trade; (Charleston, SC, USA) were used for calibrations. The contents of Na, K, Mg, Ca and Sr for the laboratory control samples were measured by using NIST Standard Reference Material\u0026reg;1640a, and the Cl contents for analogous samples were measured by using Simulated Seawater Standard (HighPS). The instructions of the ISO 11352:2012 standard were followed for estimating the analytical measurements uncertainty.\u003c/p\u003e"},{"header":"Results and discussions","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eMain geochemical features of the water samples\u003c/h2\u003e \u003cp\u003eAs indicated by the Piper diagram (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea), a Ca\u0026ndash;HCO\u003csub\u003e3\u003c/sub\u003e facies is characteristic to water samples collected from all considered sites, not only from impenetrable karst springs or from streams intercepted by caves, but also from FUS swallet. That swallet displays however a slight relative enrichment in SO\u003csub\u003e4\u003c/sub\u003e and Na, presumably as a consequence of the metamorphic and magmatic terrains which prevalently build up its catchment. In particular, the SO\u003csub\u003e4\u003c/sub\u003e enrichment could originate \u0026ndash; similarly to the situations discussed by Ulloa-Cedamanos et al. (2020) \u0026ndash; in the oxydation of small pyrite impurities that possiby occurred within the crystalline formations of the concerned watershed.\u003c/p\u003e \u003cp\u003eAt the same time, it appears that along the inferred underground flowpaths (starting from FUS swallet toward the inferred outflows PIC and PAT), the SO\u003csub\u003e4\u003c/sub\u003e and Na signatures become gradually less definite, to the detriment of the overall Ca\u0026ndash;HCO\u003csub\u003e3\u003c/sub\u003e character. In order to better illustrate this trend, an additional representation was devised for the cations and anions ternary plots of the standard Piper diagram, by multiplying the concentrations of Na, K, Cl, SO\u003csub\u003e4\u003c/sub\u003e and NO\u003csub\u003e3\u003c/sub\u003e by a factor of 10 (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb).\u003c/p\u003e \u003cp\u003eIt is reasonable to assume that the water fraction which prevails in FUS swallet is that derived from silicate weathering. At the same time, the relative contribution of this silicate-derived water is expected to diminish progressively along the underground flowpaths toward the karst springs, because of additional inflows of carbonate water originating in the hosting limestone body. Such a space-variable balance between the silicate-derived and carbonate-derived water contributions could be the cause of the two trends outlined by the Piper diagram for the sampling sites on the right side of Sohodol valley (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb): (i) the alkali-earth involvement increases from FUS swallet, toward CFUS cave stream, an further toward the inferred outflows PIC and PAT, to the detriment of the alkali contribution; (ii) the alkalinity also increases from the swallet toward the outflows, to the detriment of the sulphate ion contribution. Analogous variations, although less conspicuous, are also visible starting from CVAR cave stream toward VAR spring, both of which are situated on the left side of Sohodol valley.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003eMixing patterns between allogenic and autogenic water inputs\u003c/h2\u003e \u003cp\u003eThere was next attempted to identify natural tracers that could provide additional information on (i) underground hydrological connections within the karst region and (ii) the relative contributions of allogenic and autogenic inputs along the corresponding flowpaths.\u003c/p\u003e \u003cp\u003eThe most straightforward diagnoses in this respect should be provided by linear correlations between the concentrations of pairs of solutes that behaved conservatively. Such patterns displayed by bivariate plots indicate that two end-members of constant concentrations mix with one another in various ratios, which eventually determine the particular concentration values recorded at each sampled site. Given the existing karst setting, the two involved end-members are expected to be allogenic (silicate-derived) and autogenic (carbonate-derived) water.\u003c/p\u003e \u003cp\u003eFor the considered karst region, the tightest linear correlations between samples simultaneously collected from various locations were obtained for Na, SiO\u003csub\u003e2\u003c/sub\u003e, and Ba (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe most eloquent in terms of karst catchments delineation appeared to be two diagrams: one in which Ba concentrations were plotted against the concentrations of SiO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea), and the other in which Ba was plotted against Na (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb). In each of the two plots, mixing lines fitted to data points that corresponded to simultaneously collected samples clearly belong to two distinct sets: one set includes only the sampling sites located on the right side of Sohodol valley (filled symbols), while the other set includes only the sampling points from the valley left side (empty symbols).\u003c/p\u003e \u003cp\u003eAll samples assumed to be proxies of the autogenic (pristine carbonate) end-member plot in a narrow domain with small concentrations of SiO\u003csub\u003e2\u003c/sub\u003e (1.5\u0026thinsp;\u0026divide;\u0026thinsp;4.0 mg/L) and Na (~\u0026thinsp;0.3 mg/l), despite the fact that PIV sampling site is located on the right side of Sohodol valley, whereas TRAP is situated on the valley left side. Implicitly, the largest contributions of SiO\u003csub\u003e2\u003c/sub\u003e and Na must be provided by the allogenic end-members.\u003c/p\u003e \u003cp\u003eOne remarkable feature outlined by Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e is that the Ba/SiO\u003csub\u003e2\u003c/sub\u003e and Ba/Na concentration ratios in the allogenic end-member inferred to contribute to the left side sampling sites (CVAR and VAR) are significantly larger than the corresponding ratios of the allogenic end-member involved in the supply of the right side sampling points (FUS, CFUS, PIC ad PAT). It is accordingly suggested that: (i) on each side of the valley, distinct karst catchments developed, and (ii) significant differences exist in terms of Ba/SiO\u003csub\u003e2\u003c/sub\u003e and Ba/Na ratios between the allogenic inputs contributing to each of the two catchments.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAs a first order approach, the allogenic (silicate-derived) end-member that supplies the right side sampling points can be considered the water of FUS swallet (whose watershed contains relatively few carbonate terrains, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e). On each mixing line that includes samples simultaneously collected from the right-side sampling sites (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), the data points associated to CFUS cave stream and to PIC and PAT major outflows fall in-between the conjectured allogenic (silicate) and autogenic (carbonate) end-members FUS and PIV, respectively. It is thus suggested that FUS, CFUS, PIC and PAT sampling sites are indeed hydrologically connected (as formerly asserted by Iurkiewicz and Mangin, 1994), and that the cave stream CFUS, as well as each of the major karst outflows PIC and PAT, consist of allogenic-autogenic water mixtures. The relative input of silicate (allogenic) fraction in those mixtures progressively decreases along the conjectured underground flowpath which extends from FUS swallet to CFUS cave stream, then further to PIC and PAT major springs: such an evolution pattern is outlined by the gradually diminishing SiO\u003csub\u003e2\u003c/sub\u003e and Na concentrations (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn the case of the left side sampling sites (empty symbols in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e), a similar reduction of the silicate water contribution is suggested to occur between CVAR cave stream and VAR impenetrable spring. However, since both sampling sites are water outflows, their likely interconnection does not necessarily consist of CVAR cave stream directly supplying VAR spring; but rather that a common allogenic (silicate-derived) input reaches both water flows, where it mixes with autogenic (carbonate-derived) diffuse recharge, whose contribution is more abundant in VAR than in CVAR sampling site. Implicitly, a silicate-derived (allogenic) end-member is conjectured to exist, which has SiO\u003csub\u003e2\u003c/sub\u003e, Na and Ba contents larger than those of CVAR cave stream; so far however, the contributing inflow representing that allogenic end-member has not been identified.\u003c/p\u003e \u003cp\u003eThe Na vs. SiO\u003csub\u003e2\u003c/sub\u003e bivariate plot (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e) is the one which outlines the tightest linear correlations between data points that correspond to simultaneously collected samples. The fitted linear regressions have considered sampling sites on the right side of Sohodol valley, separately from sampling sites on the valley left side, taking into consideration the corresponding distinction revealed by the previously discussed Ba vs. SiO\u003csub\u003e2\u003c/sub\u003e and Ba vs. Na diagrams. Yet as far as Na vs. SiO\u003csub\u003e2\u003c/sub\u003e mixing lines are concerned, only little difference seems to exist between the right and left side sampling sites. This circumstance seems to indicate that not only the carbonate (autogenic) end-member proxies have similar Na/SiO\u003csub\u003e2\u003c/sub\u003e concentration ratios, but also the allogenic (silicate-derived) end-members. Therefore, by using just the Na vs. SiO\u003csub\u003e2\u003c/sub\u003e reciprocal concentration plot, it would have been virtually impossible to identify the distinction existing between the karst catchments of the right and the left sides of Sohodol valley.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eAt the same time, if the separation between the right and left sides of the valley is taken beforehand into account, it is obvious that the data points relative positions within the Na vs. SiO\u003csub\u003e2\u003c/sub\u003e diagram are fully consistent with the hydrological connections and the relative contributions of allogenic and autogenic inputs which had been conjectured based on the Ba vs. SiO\u003csub\u003e2\u003c/sub\u003e and Ba vs. Na bivariate plots. It is also worth mentioning that in all three diagrams (Ba vs. SiO\u003csub\u003e2\u003c/sub\u003e \u0026ndash; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, Ba vs. Na \u0026ndash; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, and Na vs. SiO\u003csub\u003e2\u003c/sub\u003e \u0026ndash; Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e), the data-points corresponding to samples simultaneously collected from the PIC and PAT outflows are virtually coincident. This result is consistent with the tracer test results reported in Iurkiewicz and Mangin (1994), which indicated that those two major springs are \u0026rdquo;twin\u0026rdquo; outflows of a single karst drainage system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eQuantifying relative contributions of allogenic (silicate-derived) and autogenic (carbonate-derived) water\u003c/h2\u003e \u003cp\u003eAs previously discussed, the linear trends outlined in the Ba vs. SiO\u003csub\u003e2\u003c/sub\u003e, Ba vs. Na and Na vs. SiO\u003csub\u003e2\u003c/sub\u003e diagrams (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea, \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb and \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, respectively) indicate that the corresponding solutes concentrations are controlled by binary mixing between silicate (allogenic) and carbonate (autogenic) end-members. The contribution that each of those two end-members has in a particular water sample can be assessed, similarly to the approach of Katz et al. (1998), Qin et al. (2017), or Gill et al. (2018), by a two-component mixing model. Specifically, the allogenic end-member fraction \u003cem\u003ef\u003c/em\u003e\u003csub\u003eall\u003c/sub\u003e in the sampled mixture is expressed as:\u003cdiv class=\"BlockQuote\"\u003e\u003cp\u003e \u003cem\u003ef\u003c/em\u003e \u003csub\u003eall\u003c/sub\u003e = (\u003cem\u003eC\u003c/em\u003e\u003csub\u003em\u003c/sub\u003e-\u003cem\u003eC\u003c/em\u003e\u003csub\u003eaut\u003c/sub\u003e)/(\u003cem\u003eC\u003c/em\u003e\u003csub\u003eall\u003c/sub\u003e-\u003cem\u003eC\u003c/em\u003e\u003csub\u003eaut\u003c/sub\u003e) (1)\u003c/p\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003ewhere \u003cem\u003eC\u003c/em\u003e\u003csub\u003em,\u003c/sub\u003e \u003cem\u003eC\u003c/em\u003e\u003csub\u003eall\u003c/sub\u003e, and \u003cem\u003eC\u003c/em\u003e\u003csub\u003eaut\u003c/sub\u003e are the concerned solute concentrations in the mixture, the allogenic end-member, and the autogenic end-member, respectively.\u003c/p\u003e \u003cp\u003eTaking into account that the major karst springs PIC and PAT had been shown to discharge mixtures of allogenic and autogenic water, the allogenic end-member fraction which contributed to each of those two outflows could be computed by means of Eq.\u0026nbsp;(1). The concentration of PIV small spring was adopted as autogenic end-member, and the FUS swallet concentration as allogenic end-member.\u003c/p\u003e \u003cp\u003eThe computations were conducted for two distinct sampling dates, October 2023 and May 2023; and for each of those sampling operations, separate estimations were performed by using each of the three distinct tracers: SiO\u003csub\u003e2\u003c/sub\u003e, Na and Ba. The obtained values are listed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eAllogenic water fractions in the karst springs PAT (the Oct 2023 sampling) and PIC (the Oct 2023 and May 2023 samplings). For each instance, there are indicated the fractions separately computed by means of each of the tracers SiO\u003csub\u003e2\u003c/sub\u003e, Na and Ba\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"5\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eSampling site\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003ePAT\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003ePIC\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c2\" namest=\"c1\"\u003e \u003cp\u003eSampling date\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eOct 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eOct 2023\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMay 2023\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003eTracer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.72\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eNa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.77\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.79\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e0.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e0.59\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e0.74\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eIn May 2023, allogenic water fractions could be computed only for PIC spring (since PAT spring was not sampled at that date). Quite consistent allogenic water fraction values (around 0.7) were obtained by means of each considered tracer (SiO\u003csub\u003e2\u003c/sub\u003e, Na and Ba).\u003c/p\u003e \u003cp\u003eThe allogenic fraction values obtained for the same spring in October 2023 by using either SiO\u003csub\u003e2\u003c/sub\u003e, or Na as a tracer, were consistent with each other and larger (around 0.8) than the values obtained in May 2023. The value (0.59) based on Ba concentrations appeared however to be less accurate.\u003c/p\u003e \u003cp\u003eFor the October 2023 sampling of PAT spring, computations based on SiO\u003csub\u003e2\u003c/sub\u003e also provided similar fractions with the computations based on Na (slightly smaller than 0.8, on the average); whereas the value based on Ba concentrations appeared to be less reliable (0.47). There can be concluded that PAT spring included a slightly smaller fraction of allogenic water than the sample simultaneously collected from PIC spring.\u003c/p\u003e \u003cp\u003eIn more general terms, the allogenic fraction in PIC outflow during the high water stage (May 2023) resulted to be smaller than during the low water period (October 2023). It is implicitly suggested that on the occasion of flood episodes, autogenic recharge increases, on the whole, at a faster rate than the allogenic one. Such a general conclusion appears to be largely consistent with more detailed results provided by Lorette et al. (2021) for a flood episode recorded in a karst region of southern France.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003ePossible controls on the Ba abundance of the allogenic water inputs\u003c/h2\u003e \u003cp\u003eA distinctive feature of Sohodol karst region consists in the significantly smaller Ba/SiO\u003csub\u003e2\u003c/sub\u003e and Ba/Na ratios displayed (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e) by the allogenic supply to the valley right side sampling sites (i.e. the FUS swallet), as compared to the analogous ratios recorded in the case of the left side allogenic input (the one which supplies CVAR and VAR). Such a setting suggests that also the rock formations leached by the corresponding allogenic water flows could considerably differ from each other in terms of their Ba/SiO\u003csub\u003e2\u003c/sub\u003e and Ba/Na ratios.\u003c/p\u003e \u003cp\u003eIn an attempt to substantiate such a hypothesis about water-rock interactions in the considered watersheds, two additional plots have been constructed with data provided by whole rock chemical analyses: Ba/SiO\u003csub\u003e2\u003c/sub\u003e vs. Ba (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea) and Ba/Na vs. Ba (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb). For devising the diagrams, since most of the Sohodol watershed is developed on Lainici-Păiuş rock formations, within which three types of magmatic intrusions had been identified, use has been made of the whole rock chemical composition data presently available for those intrusions: namely, the analyses provided by Savu et al. (1974) for leucogranitoid dykes and sills collected from the Jiu and Şuşiţa valleys, those provided by Savu et al. (1971) for granites collected from the Suseni pluton (located immediately to the east of Sohodol watershed), and those provided by F\u0026eacute;m\u0026eacute;nias et al. (2008) for Motru Dyke Swarm andesites and basaltic andesites (collected from the areas designated as Jiu Susita and North Bistrita). Unfortunately, no similar chemical analyses are also available for any of the Lainici-Păiuş metamorphic rocks.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigures\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea,b indicates that leucogranitoids, together with the Suseni pluton granites, form a distinct group of Ba-rich rocks. Consequently, prevalent leaching of such lithologies might explain the Ba-enrichment displayed by the allogenic input conjectured to supply the karst water sampling sites VAR and CVAR located on the left side of Sohodol valley. Alternatively, Ba contents of the Motru Dyke Swarm rocks are significantly smaller (by one order of magnitude in some cases) than those of the granites in Suseni pluton, or of the leucogranitoids. Therefore, the Ba-poor water of FUS swallet may indicate that in the corresponding sinking stream watershed, dykes of Motru Swarm type are abundant.\u003c/p\u003e \u003cp\u003eBased on the previously mentioned rock samples analyses, a Na/SiO\u003csub\u003e2\u003c/sub\u003e vs. Ba bivariate plot has also been constructed (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ec). It clearly shows that for the considered rock formations, the Na/SiO\u003csub\u003e2\u003c/sub\u003e ratios variation range is much narrower than the variation range of either the Ba/SiO\u003csub\u003e2\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003ea), or the Ba/Na (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eb) ratios. In fact, the Ba contents of the rock samples are clearly uncorrelated with the corresponding Na/SiO\u003csub\u003e2\u003c/sub\u003e ratios, and those ratios only slightly vary between one lithological type and another. The latter observations could explain why all allogenic end-members involved in the supply of the sampled karst waters did not differ significantly from each other in terms of their Na/SiO\u003csub\u003e2\u003c/sub\u003e ratios, irrespective of the catchment to which the sampling points belonged (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAll in all however, more elaborate interpretations on the water-rock interaction topic are not warranted, due to the paucity of rock chemistry data available for the considered region, and especially because of the complete absence of such information pertaining to the metamorphic formations.\u003c/p\u003e \u003cp\u003eOne further point to be emphasized is that on most water sampling occasions, all three considered natural tracers, Na, SiO\u003csub\u003e2\u003c/sub\u003e, and Ba were more concentrated in the allogenic (silicate-derived) water input than in the autogenic (carbonate) one (Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e). On a single instance however (the samples collected in May 2023 from the right side of Sohodol valley), the concentrations of Ba in the autogenic end-member exceeded the corresponding concentrations of the allogenic end-member. The particular behaviour recorded on that high water period could be the result of an even larger fraction of Ba-poor silicate rocks being temporarily involved in providing allogenic recharge to FUS swallet. Still one cannot exclude an alternative explanation, that would consider disturbances associated to the intense seismic activity (Radulian et al. 2023) which has affected the considered area for a few months, starting with February 2023.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003eComparison with previously reported Ba vs. Na concentration relationships in karst aquifers with allogenic recharge\u003c/h2\u003e \u003cp\u003eIn terms of Ba and Na behaviour, the closest analogue reported so far for the Sohodol valley sampling sites appears to be the H\u0026eacute;rault stream watershed, in southern France: there, simultaneous enrichments in Na and Ba were displayed by silicate-derived sinking streams, while the correspondingly connected karst outflows were noticed to be depleted in both elements (Petelet at al. 1998).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFor two karst springs sampled by Moldovan et al. (2021) in the South Carpathians (Romania) and designated as GWR1 and GWR3, T\u0026ouml;r\u0026ouml;k et al. (2023) have conjectured that they likely included a silicate-derived (hence allogenic) water contribution, and that their content of dissolved Na and Ba originated mainly in carbonate rocks weathering. The latter inference could suggest that the concerned outflows were analogues of the PIV and TRAP springs, which had been shown in the present study to discharge only pristine carbonate water. A similarity with springs like PIV and TRAP would however be at odds with the silicate water contribution inferred by T\u0026ouml;r\u0026ouml;k et al. (2023) for the GWR1 and GWR3 outflows; on the other hand, an allogenic input would explain the GWR1 and GWR3 springs enrichment in Ba and Na (with concentrations that significantly exceeded, in most instances \u0026ndash; Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e - those of PIV and TRAP springs of Sohodol watershed). One cannot therefore exclude the possibility that although small amounts of Ba and Na dissolved in the springs addressed by Moldovan et al. (2021) and T\u0026ouml;r\u0026ouml;k et al. (2023) were derived from carbonate rocks dissolution, larger amounts actually originated in allogenic (silicate-derived) water contributions.\u003c/p\u003e \u003cp\u003eIn the case of Gort Lowlands karst network (western Ireland), aqueous concentrations of Ba and Na reported by Gill et al. (2018) proved to be linearly correlated (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e), outlining binary mixing between allogenic and autogenic water inputs. Similarly to the Sohodol valley setting, the allogenic end-member is a sinking stream, while the autogenic end-member proxy is a particular karst spring. However, no cave streams have been sampled in that case, but instead, samples were collected from water surcharging out of the conduit network: on the mixing line, the latter samples plot \u0026ndash; similarly to cave stream samples of Sohodol valley \u0026ndash; between the swallet and the karst catchment main outflow. It is thus indicated that the allogenic water relative contribution gradually diminishes along the underground flowpaths, to the benefit of the autogenic inputs contribution.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eNotice that Gort Lowlands is, to the best of our knowledge, the only karst setting reported so far where Na is more abundant in the autogenic end-member than in the allogenic one (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e). This specificity (which appears to mirror the impact of the nearby seawater - Gill et al. 2018) did not alter however the binary mixing pattern which indicates that along the undergound flowpaths, the autogenic water contribution progressively increases to the detriment of the allogenic input contribution.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe trace element Ba, in conjunction with the major constituents SiO\u003csub\u003e2\u003c/sub\u003e and Na, have been used as natural tracers for investigating underground drainage patterns in karst catchments which are located in the Sohodol valley and are subject to allogenic (silicate-derived) recharge.\u003c/p\u003e \u003cp\u003eAdvantage was taken of the fact that various silicate rocks included in the watersheds that supplied allogenic water to the considered karst aquifers did not significantly differ from each other in terms of either Na, or SiO\u003csub\u003e2\u003c/sub\u003e contents; instead, Ba contents differed by up to one order of magnitude between one type of silicate rock and another. As a result, it was possible to distinguish a karst catchment supplied by Ba-rich allogenic inputs, from another karst catchment supplied by Ba-poor allogenic water; however, such a distinction could not have been outlined by using only the sampled waters concentrations of SiO\u003csub\u003e2\u003c/sub\u003e and Na.\u003c/p\u003e \u003cp\u003eWhile most previous studies concerned with allogenic and autogenic inputs in karst aquifers had addressed only surface rivers and karst springs, the present investigation has focused on particular underground flowpaths which connected a swallet to a cave stream, and further to the final karst outflows. For each of the three natural tracers which had been considered (Na, SiO\u003csub\u003e2\u003c/sub\u003e and Ba), the concentrations distribution consistently outlined a gradual reduction of the allogenic recharge relative contribution, to the benefit of the relative contribution of the autogenic (carbonate) water inputs: from a swallet to a cave stream, and further from cave streams to the final karst outflows (for which the included fraction of allogenic water always remained important, about 70\u0026ndash;80%, with the larger percentage being recorded during a low water stage). These results further support the reliability of the considered natural tracers for estimating the relative contributions of allogenic and autogenic inputs in karst waters.\u003c/p\u003e \u003cp\u003eA synopsis of the considered natural tracers ability to elucidate underground drainage patterns in the Sohodol valley karst area is provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e, which shows that: (i) all three considered solutes (Na, SiO\u003csub\u003e2\u003c/sub\u003e and Ba) behave in the considered setting conservatively; (ii) the outlined binary mixing patterns indicate that from a surface stream swallet toward a cave stream, and further from cave streams toward karst outflows, the autogenic water relative contribution gradually increases, to the detriment of the relative contribution of allogenic inputs; (iii) in a reciprocal concentration plot including Ba, two karst catchments can be clearly distinguished from each other, whereas in an analogous SiO\u003csub\u003e2\u003c/sub\u003e vs. Na diagram, such a distinction is virtually undetectable.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBoth in Romania and worldwide, fluviokarst environments with allogenic recharge characteristics similar to those encountered in Sohodol valley are not uncommon. In such settings, the utilization of the three considered natural tracers - Ba in conjunction with SiO\u003csub\u003e2\u003c/sub\u003e and Na - could be further tested for investigating underground drainage patterns within the corresponding karst catchments.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003cstrong\u003eConflict of interest\u003c/strong\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eConceptualization, HM, NC, MV, CN and GC; methodology, NC, HM, CM, MV, CN, GC, AT and LN; formal analysis, NC, HM, CM, GC, AT, LN and MV; investigation, NC, HM, GC, and MV; writing \u0026ndash; original draft preparation, HM, NC, MV, and LN; writing \u0026ndash; review and editing HM, NC and MV. All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eField operations greatly benefitted of the valuable support provided by Agata Teodorescu, Mădălina Constantinescu, Emilian Stoica, Doru Măcreanu, Mircea Vlădulescu and Vlad-George Cruceru. Our gratitude is also extended to Floarea Răducă for her dedicated assistance in the laboratory work.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eAnthony DM, Granger DE (2007) An empirical stream power formulation for knickpoint retreat in Appalachian Plateau fluviokarst.\u003cem\u003e \u003c/em\u003eJ Hydrol 343:117-126. https://doi.org/10.1016/j.jhydrol.2007.06.013\u003c/li\u003e\n\u003cli\u003eAmerican Society for Testing and Materials (1995) ASTM-D516-07. 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Washington DC. https://www.epa.gov/sites/default/files/2015-12/documents/6020b.pdf\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":"karst, allogenic recharge, hydrochemistry, natural tracers, barium, Romania","lastPublishedDoi":"10.21203/rs.3.rs-4317845/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4317845/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn a fluviokarst region, three seldom used natural tracers, SiO\u003csub\u003e2\u003c/sub\u003e, Na and Ba, were considered for tracking the allogenic, silicate-derived water contribution to cave streams and to final karst outflows. The concerned allogenic recharge originates in watersheds that consist of metamorphic formations intruded by magmatic rocks, for which available whole rock chemistry data indicate rather uniform contents of SiO\u003csub\u003e2\u003c/sub\u003e and Na, but contrasting (up to one order of magnitude) contents of Ba. All three considered natural tracers proved to behave, along karst flowpaths, conservatively, and indicated binary mixing between allogenic and autogenic inputs. However, only the dissolved Ba concentrations enabled chemical distinction to be made between two separate, adjacent karst catchments: one having allogenic inputs presumably derived mainly from the weathering of Ba-rich rocks (essentially granites), while the other had allogenic recharge originating mostly in the weathering of Ba-poor formations. In contrast, if only the sampled waters SiO\u003csub\u003e2\u003c/sub\u003e and Na concentrations had been considered, it would have been virtually impossible to establish if the two adjacent karst catchments were distinct - or not - from each other. When considering each of the two karst catchments separately, the concentrations distribution of each of the three natural tracers, SiO\u003csub\u003e2\u003c/sub\u003e, Na and Ba, consistently indicated that between a swallet and a connected cave stream, then further between cave streams and final karst outflows, the allogenic water relative contribution gradually diminished to the benefit of autogenic water.\u003c/p\u003e","manuscriptTitle":"Dissolved Ba as discriminator between two adjacent karst catchments that are both subject to allogenic recharge (Sohodol valley, Vâlcan Mountains, Romania)","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-02 08:38:11","doi":"10.21203/rs.3.rs-4317845/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"checksComplete","content":"","date":"2024-04-26T00:32:39+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-26T00:32:39+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Earth Sciences","date":"2024-04-24T11:24:01+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":"714c9ae2-2afe-4652-8344-0c8e205b1927","owner":[],"postedDate":"May 2nd, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-12-02T15:59:31+00:00","versionOfRecord":{"articleIdentity":"rs-4317845","link":"https://doi.org/10.1007/s12665-024-11990-8","journal":{"identity":"environmental-earth-sciences","isVorOnly":false,"title":"Environmental Earth Sciences"},"publishedOn":"2024-11-28 15:56:50","publishedOnDateReadable":"November 28th, 2024"},"versionCreatedAt":"2024-05-02 08:38:11","video":"","vorDoi":"10.1007/s12665-024-11990-8","vorDoiUrl":"https://doi.org/10.1007/s12665-024-11990-8","workflowStages":[]},"version":"v1","identity":"rs-4317845","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4317845","identity":"rs-4317845","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}