Accelerated Carbonates Dissolution Caused by Anthropogenic Acidification - Contrast of Watershed Soils to Lake Sediments in Taihu Region, China

Accelerated Carbonates Dissolution Caused by Anthropogenic Acidification - Contrast of Watershed Soils to Lake Sediments in Taihu Region, China | 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 Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Accelerated Carbonates Dissolution Caused by Anthropogenic Acidification - Contrast of Watershed Soils to Lake Sediments in Taihu Region, China Yu Tao, Jia Binyang, Wang Rui, Deng Yixiang, Zhuo Xiaoke, Cheng Zhonghua, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-1556696/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 7 You are reading this latest preprint version Abstract Anthropogenic disturbances have greatly changed the water chemistry in Taihu lake, however, how soil carbonates responded to the long-term human-induced acidification received less attention likely due to the “acid-insensitive” region of Taihu watershed. In this work, we investigated soil carbonate concentrations from different land uses in the upstream of the lake and sediment carbonate profiles in the lake, to explore the linkage of carbonates dissolution in the land and sedimentation in the lake. The result showed that the wheat-rice surface soil, the most acidification-impacted by fertilization and acid deposition, had significantly lower pH than vegetable and wetland soils (p < 0.05). Meanwhile, the carbonate concentration in wetland soils, only impacted by acid deposition, was significantly higher than that in wheat-rice and vegetable soils (p < 0.05). The pH profile of fertilized soils, with an increasing trend from the surface to bottom, further indicated the acidifying effect of fertilization. Although the average soil pH across all land uses was 6.6 in the upstream of the lake, remaining carbonate buffering system, the significant carbonate decrease especially in surface soils evidenced the definite carbonate dissolution by acidification, which is cumulative and irreversible. Contrary to the topsoils, the sediment carbonate concentration presented an increasing trend from the depth of 15cm (denoting around the early 1980s) to surface, indicating that lake sediments are major sink of carbonate Ca and Mg from the watershed, particular under an alkaline lake environment caused by frequent algae blooms in the past decades. In addition, Ca/Mg ratio in the sediment, having higher values in a higher pH environment, was quite different from the watershed pattern, suggesting different biogeochemical processes they underwent during their transportation and sedimentation. The effects of acidification-altered re-distribution of carbonate Ca and Mg and Ca/Mg ratio in the terrestrial and aquatic environments deserve wider considerations of ecosystem consequence. Carbonates Acidification Soil and sediment Ecosystem Taihu Watershed Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Calcium (Ca) and magnesium (Mg) are abundant elements in the earth surface system and are necessary macronutrients for the human and other living beings. These base cations are important in the maintaining of terrestrial and aquatic ecosystems, and their existence and concentration can regulate or alter species distribution (Weyhenmeyer et al., 2019) and ecosystem change (Bérangère et al., 2016). In the natural system, these rock-derived elements retain dynamic balance between terrestrial and water systems, however, this balance has been changed by the increasing human disturbance. A typical trend of this change is the significant increase in water hardness or alkalinity at the regional (Yu et al., 2013) or continental scale (Kaushal et al., 2018). One of the important driving forces to accelerate the base cation losses from lands to waters is human-induced acidification, generally caused by acidic gas emissions (Yu et al., 2013) and nitrogen fertilizer applications (Liang et al., 2019). Although soils acidify under natural conditions very slowly, usually over hundreds to millions of years, this process has been greatly accelerated by human activities (Guo et al., 2010). Atmospheric deposition caused acidification, commencing in Europe and eastern North America in the middle of the 20th century, also known as acid rain, has caused a series of environment problems and caused worldwide concerns (Bérangère et al., 2016). For example, atmospheric deposition of sulfide has been the dominant factor causing widespread and deleterious impacts on aquatic and terrestrial ecosystems (Mitchell and Linkens, 2011), and global land has received more than 50 kg ha −1 accumulated N deposition during 2000–2010, which has been documented as the main causation of soil acidification in terrestrial ecosystems (Tian et al., 2015). In addition, long-term N enrichment via fertilization in soils is another factor causing environment acidification (Guo et al., 2010). This is particularly true in China as N fertilizer consumption has rapidly increased to maintain or increase crop production. The national average N input was up to 311 kg N/ha/yr in 2010 in China, much higher than the world average, and overuse of N fertilizer contributes substantially to regional soil acidification in this country (Qichao et al., 2018). Acidification has resulted in profound environment problems and ecosystem damages. In oceans, acidification-induced carbonate dissolution could produce substantial consequences to the ecology of calcifiers (Sulpis et al., 2018), as carbonates such as calcite, constitute the shells of most coccolithophores and planktonic foraminifera (Sulpis et al., 2021). In terrestrial systems, acidification can result in soil quality degradation and soil environmental damage by accelerating lossess and depletion of soil nutrients, e.g., Ca 2 + , Mg 2 + , K + (Slessarev et al., 2016). Additionally, it can mobilize toxic metals such as Al 3+ and Mn 2+ and elevate their available concentrations in the soil solution, thus resulting in deleterious impacts on both aquatic and terrestrial ecosystems (Mitchell and Likens, 2011), and even affecting public health (Wang et al., 2018). Furthermore, serious soil acidification may induce the destruction of carbon balance in terrestrial ecosystems with large losses of soil carbon (Yang et al., 2012), and may be a significant threat to species diversity and terrestrial ecosystem functioning (Chen et al., 2013). Rock derived base cations (particularly Ca 2+ and Mg 2+ ) are critically important in buffering soil acidification at the early stage (Yang et al., 2012). When the environment pH is higher than 7.5, soil acidification is largely buffered by calcium carbonate; when pH at the range from 4.5 to 7.5, the acidification process is mostly buffered by base cations, such as exchangeable Ca 2+ , Mg 2+ , K + , etc. (Tian at al., 2015). However, with the development of acidification, depletion of carbonates or base cations and a series of consequent environment problems are expected. Once surrounding pH < 4.5，these base cations become severely deficient, and non-base cations (Al 3+ , Fe 3+ ) are mobilized to buffer against the acidification. It is reported that global soils may have shifted from base cation buffering to Al 3+ buffering due to anthropogenic acidification (Tian at al., 2015). Base cation depletion will in turn cause further ecosystem problem. A recent study showed that, in the northeastern United States, forest growth declined along with decreased soil calcium availability, indicating that the regional acid rain had depleted soil Ca to the point where it may be a limiting nutrient (Bérangère et al., 2016). China is the third major acid rain region on the globe after Europe and America, and Taihu region is one of the most serious acid rain areas in China, with the average atmospheric deposition pH<5 during 2011-2015 (Tao et al., 2016). In addition, intensive N fertilizer applications (515 kg N/ha/yr) in this region (Qichao et al., 2018) even exacerbated local soil acidification. Consequently, in the past decades, the hardness (Ca 2+ and Mg 2+ ) of Taihu lake water increased by three folds (Yu et al., 2013) due to accelerated chemical weathering caused by acidification in the watershed. The water quality and eutrophication issues in the Taihu watershed have drawn worldwide attentions and have been well documented (Guo et al., 2007). However, carbonate dissolution resulting from acid deposition and nitrogen fertilization in the watershed so far has been rarely reported, most likely due to the “acid–insensitive” characteristic of this region, i.e., an abundance of carbonates distribution in the watershed (Chetelat et al., 2008). However, the carbonate dissolution, consequent base cation losses and the lake responses deserve a closer attention, as these geochemical processes will likely produce profound, if not immediate, and irreversible effects on the both terrestrial and aquatic ecosystems. This study aims to (1) characterize the distribution of calcium and magnesium carbonates in soils of different land uses under the acidification background in Taihu watershed,（2）elucidate carbonates distribution on the profile of lake sediments, and（3）explore the linkage between the terrestrial base cation loss and lake sedimentation. This work is expected to provide basis for the quantitative modelling of carbonate dissolution and subsequent evaluation of the ecosystem effects in the acidification-impacted regions. 2. Material And Methods 2.1 Site Delineation The Taihu watershed is located in the downstream of the Yangtze River. It is one of the most economically developed and most densely populated areas in China, and it has been the breadbasket through the long Chinese history. Our study area involved the upstream river systems in the Taihu watershed and Taihu lake (Figure 1). The general topography of the Taihu watershed is characterized by hilly areas in the northwest and southwest to the lake, where river networks in this watershed originate and discharge into Taihu lake, thus composing the major linkage between the land and water environment through the river flux delivery (Figure1). Downstream of the hilly areas is the alluvial plain and Quaternary deposits, where the highly mature soils have undergone intensive weathering and leaching. Therefore, this work focused on the soils in the upstream drainage systems in the watershed to explore the linkage of the carbonate dissolution and sedimentation between the land and the lake. The matrices in the Taihu watershed are dominated by clastic rocks and carbonates (Chetelat et al., 2008), and the soil type in this region mainly consists of the yellow-brown soil, red soil, and paddy soil. Due to carbonates distribution in this watershed, considerable carbonate concentration is observed in local soils, which plays a major buffer to the acidification resulting from acid rains and nitrogen fertilization. According to the document, the concentration of calcium carbonate in various soils in Jiangsu province (a major area in the upstream of the Taihu watershed) ranged from 0.4-100g/kg (by gasometric method), of which the soil area with calcium carbonate<10g/kg accounted for approximate 50% of the total soil area (Jiangsu soil survey office, 1995). Carbonate rocks also appear in the Xishan Island in Taihu lake (Figure 1), where the carbonates constitute the main part of the hills and the carst caves also exist, which is a famous tourism resort. Taihu lake is characterized with two distinctive lake parts, i.e., the algae-dominated part in the northwest lake (NW), where surrounding pH is higher due to algae bloom effects, and the macrophyte-dominated part in the southeast lake (SE) (Figure 1), where the environment pH is relatively lower than the NW part. The environmental differences between the two lake parts were documented in our previous work (Yu et al., 2018). The Taihu region, located in the Yangtze Delta, has long been a breadbasket through the Chinese history, and it is one of the most economically developed areas in China, with the highest population density and high urbanization rate in this country. Due to the intensive anthropogenic disturbance, the Taihu watershed and the lake has undergone remarkable environmental changes in the past decades (Shi et al., 2015). One of the environmental concerns was acidification caused by both acid deposition and nitrogen fertilization application. This region is one of the most serious acid rain areas in China due to acidic gas emissions (Tao et al., 2016); on the other hand, the nitrogen fertilizer application in the local farmland (515 kg N/ha/yr) was much higher than the national average (Qichao et al., 2018). As a consequence, the losses of the terrestrial base cations and significantly increased hardness (Ca 2+ +Mg 2+ ) of the lake water during past decades have been greatly accelerated (Yu, et al., 2013) and will likely produce effects on the aquatic ecosystem (Weyhenmeyer et al., 2019). However, this issue so far has received much less attention than water pollution and eutrophication of this famous lake. 2.2 Sampling and sample pre-treatment The river systems, the lake, and all watershed soil and lake sediment sampling sites in this study are shown in Figure 1. The sampled carbonate sites in the watershed and small islands with carbonate rocks nearby Xishan island (north to Xishan island) in Taihu lake are illustrated in Figure S1. All Soil and sediment samples were taken in the six field investigations during 2017-2019, with 20% sampling sites repeated to check the reproducibility of the tests. The soil sites were distributed along the two major upstream river systems in the northwest of Taihu lake (Figure 1) so as to explore the linkage between the land and the lake. The soil samples were taken from four land uses, i.e., the dominant crop land or wheat-paddy rotation land soil and vegetable land soil, which are impacted by both chemical N fertilizer addition and acid deposition; wetland and forest land soil, both of which are only impacted by the acid deposition. All soil samples were taken with a soil corer sampler with a diameter of 5cm, and the soil column was segmented into 3cm sections from the surface to bottom in situ. Soil sections were preserved at around 4℃ until further processing in the laboratory. Figure 1 The river networks upstream of Taihu lake and soil sampling sites in different land uses and sediment sites in different lake part (Dash square indicates Dapu town near the lake, in which sampled soils were regarded to have identical matric for contrast of acidifying effect of different “treatments”) The lake sediment sites, designed to reflect the entire lake character, were located in the two distinctive parts of the lake-the northwest (NW) and the southeast (SE) lake area, with 9 sites at the representative lake bays and the open lake in the NW part and 4 in the SE part (Figure 1). The sediment samples were taken using a gravity core sampler with a diameter of 10 cm and length of 50 cm. Each sediment core was sliced into 2 cm sections from the surface to bottom in situ to explore the profile chronological characteristics. All segmented sediments were preserved at around 4℃ until further processing in the laboratory. In the laboratory, all soil and sediment samples were first freeze-dried and then ground and sieved with a 100-mesh sieve to obtain the <63 μm fraction, which was prepared for parameter measurements. 2.3 Sample measurement and quality control For the pH measurement of each soil and sediment sample, the extracted solution was first prepared by adding Milli-Q water to the sieved soil or sediment sample (mass ratio of water/soil or sediment= 5:1). The mixture was then mechanically shaken at 250 r/min at 25℃ for 24 h. After shaking, the overlaying solution was measured for pH using HACH (HQ30d) multi-functional water quality parameter instrument. The acid-extracted Ca and Mg of soil and sediment samples were extracted using 1M NaAc adjusted to pH =5.0 with acetic acid (HAc), which is regarded as carbonate combined species of Ca or Mg (Tessier et al., 1979). Then the extracted supernatant was analyzed for Ca and Mg concentration using the atomic absorption spectroscopy method (AA240FS/GTA120). Nitrogen species (NH 4 + , NO 3 - and total nitrogen) of soil samples were analyzed using spectrophotometry (Shimadzu, UV-1800). Parallel tests and the reference sample (GSD-10) were used for the analytical quality assurance in the sample processing and test. The relative standard deviation (RSD) of replicated tests was <25% and the recovery of the reference sample tests was 87-112% (for Ca) and 83-106% (for Mg). 2.4 Data manipulation Logarithm transform (for correlation analysis) or normalization (for column plots) of the acid-extracted Ca/Mg raw data was utilized in the graphic presentation to eliminate large variance and make the results comparable at the same scale. The column plot was used to summarize and contrast the distribution of measured results. Data distribution was tested prior to the statistical analysis/calculation to select the appropriate parametric/non-parametric test. The Pearson coefficient was calculated based on accepted normal distribution assumption otherwise nonparametric coefficient was calculated in the correlation analysis. Statistical comparison was based on independent-samples t-test (for two variables) or One-Way ANOVA (for three or more variables). Linear regression was used to explain how the observed factor (variable) affected the target variable. A significance level of 0.05 was used for the statistical testing. All data calculations, statistical analyses, and mapping were performed with Origin 9.3, SPSS 23, and ArcGIS 10. 3. Results And Discussion In this study, acid-extracted Ca and Mg and relevant parameters such as pH and acid-extracted Ca/Mg ratio of all soils and sediments were highlighted to elucidate how the acidification impacted carbonate bound Ca or Mg in different land uses and in the lake sediment. 3.1 Watershed soils Our field data showed that both calcium carbonate and magnesium carbonate concentrations of the four land use soils presented a significantly positive correlation to soil pH (Figure 2a and b), indicating that pH is an important regulator of soil carbonate concentrations. This positive correlation between pH and acid-extracted Ca or Mg also implies higher calcareous soils having stronger buffering capacity against acidification, and pH decreasing with calcium and magnesium carbonates losses at the watershed scale. A negative correlation between pH and Ca/Mg ratio was observed in all land use soils (Figure 2c), which indicates that at the same pH condition, magnesium carbonate is more likely to dissolve and run off than calcium carbonate. Figure 2 also showed Carbonate Ca or Mg and Ca/Mg having the least variations in wheat-rice land soils, and the largest variations in forest soils, and we supposed that this variation pattern was largely associated with the acidified extent. Figure 2 Correlation between soil pH and acid-exacted Ca (a), Mg (b) and Ca/Mg ratio (c) in different land uses The examined parameters on soil profiles can further explain how acidification affected their variations in different land use soils and at different depths. The surface soils are more susceptible to acidification. pH of all soils ranged from 4.3 to 8.5, with the average of 6.6 ± 0.8. Whereas the surface soil (0-15cm) of four land uses had significantly different pH, and the wheat-rice soil pH (mean=6.34) and forest soil pH (mean=6.27) were significant lower than vegetable and wetland soils (p<0.05), while there was no significant difference between wheat-rice soil pH and forest soil pH, and between vegetable and wetland soils (Figure 3a). The wheat-rice soils having the lowest pH in this watershed is reasonably well understood as the wheat-rice land simultaneously received two acidifying processes, i.e., intensive N fertilization and acid deposition in this region. Furthermore, there existed an observable pH gradient down the soil depth in the vegetable and wheat-rice soil (Figure 3a), indicating N fertilization played a significant role in the acidification in contrast to forest and wetland soil profiles. Previous study using 11 year of continuous N addition experiment showed that excess N inputs significantly decreased soil pH, typically with the topsoil pH lower than subsoil pH (Lu et al., 2021), which is in good agreement with our field findings. It seems unusual that the forest soils, without impacts of fertilization, had the similar surface soil pH to the wheat-rice soil, and we attribute this to two factors. On the one hand, the forest lands are generally located in the upstream hilly areas in the watershed, where the bed rocks, based on our field investigation, are mostly silicates and their weathered products are acidic. On the other hand, eluviation is relatively intensive in hilly areas, which caused further lower soil pH with the losses of cations (Pan et al., 2018). Consistent with the positive correlation between soil pH and carbonates (Figure 2), the acid-extracted calcium and magnesium concentrations of the surface soils (0-15cm) were the lowest in the wheat-rice soil (Figure 3b and c), which is most acidified in the four land use soils due to dual impacts from acid deposition and intensive N fertilization. And the carbonate concentration was the highest in the wetland topsoils (Figure 3b and c), which are generally located in the plain areas and only impacted by acid deposition but no fertilization compared with wheat-rice and vegetable lands. It is noticeable that carbonate Ca and Mg were higher in the forest land than in the wheat-rice land, especially for the topsoils (Figure 3b and c), which is due to the harvest removal of base cations in wheat-rice lands, causing further decline in these cations (Qichao et al., 2018). This also explained why wetland soils had the highest carbonate Ca and Mg concentrations. Figure 3 Constras of soil pH, acid-extracted Ca and Mg and Ca/Mg at different depths of different land uses (y-axis for carbonate concentrations is normalized coordinate) Bedrock weathering has strong controls over the concentration of Ca and Mg in the watershed soils, which in turn affects the Ca/Mg ratio of the soil (Rhodes et al., 2001). In the Taihu watershed, soils in carbonate areas (Figure S1) are characterized by the highest Ca and Mg concentration and Ca/Mg ratio. In addition, acidification exerts considerable impacts on Ca/Mg ratio as indicated in Figure 2c. Soil profile of the wheat-rice land, with a higher acidified degree in the topsoil than in the subsoil (Figure 3a), further illustrated that Ca/Mg ratio presented a distinct decline down the soil depth (Figure 3d), indicating preferential dissolution and loss of magnesium carbonate over calcium carbonate at the same pH surroundings. Soil pH and carbonates are parent material dependent (Qiquan et al., 2020). In the carbonate areas in this watershed (Figure S1), the surface (0-15cm) soil pH and acid-extracted Ca or Mg were significantly higher than in the non-carbonate areas, and even the vegetable soils in the carbonate region, impacted by both N fertilization and acid deposition, had higher pH and carbonate concentrations than those in non-carbonate regions. For example, the mean pH of 7.62 in carbonate surface soils was significantly higher than that in other soils (mean pH=6.37, p<0.01); and the mean acid-extracted Ca and Mg concentrations in the surface soil from carbonate areas were 1993.5 mg/kg and 183.8 mg/kg, respectively; while in the non-carbonate areas they were 284.3 mg/kg and 38.2 mg/kg, respectively. In spite of parent material control, previous field experimental result suggested that proton produced by nitrification played a dominant role in acidifying soil and promoting cation release (Li et al., 2018), and this process can be expressed by NH 4 + + 2O 2 =NO 3 - + H 2 O + 2H + . A previous study identified a critical level of 200 kg ha − 1 yr − 1 for N fertilizer use, above which soil acidification would be promoted (Qiquan et al., 2020). Our field observations confirmed these mechanisms. In the Taihu watershed, the average N inputs (515 kg /ha/yr) in the farmlands are much higher than that (Qichao et al., 2018), resulting in more intensive acidification. Our findings highlighted that, even in the carbonate areas, acidification by N fertilization was significant. In the Wu Xing carbonate area (Figure S1), for example, the average pH (=7.77±0.10) of the vegetable topsoil was significantly lower than that of the wetland (pH=8.26±0.14, p<0.01, Figure S2). The difference of 0.49 pH units can be ascribed to N fertilization in the vegetable land, because both soils received the identical acid deposition. In addition, the similar soil pH of hilly carbonate areas to the vegetable soil (Figure S2) again indicated the impact of eluviation on the soil pH even in carbonate regions. To further identify the role of acid deposition and nitrogen fertilization in the soil acidification and base cation losses, we focused on the field of Dapu town (indicated by the dashed square area in Figure 1) near Taihu lake, where the soil matrices of different land uses are identical. Therefore, we can regard the soil of different land uses as different “acidification treatments”, i.e., only acid deposition in wetland soils and acid deposition + N fertilization in wheat-rice soils. By examining the relationship between nitrogen species and soil pH, we found that ammonium (NH 4 + -N) or nitrate (NO 3 − -N) had a correlation to soil pH, but not total nitrogen. Thus, we used NH 4 + -N+NO 3 − -N (inorganic nitrogen, IN) to explore the soil acidification effect. The result showed that, for the topsoil (0-15cm), the soil pH was significantly positively correlated with the IN concentration for both wheat-rice land and wetland, and the linear regressions for both land soils were nearly parallel, with an intercept difference of 0.56 (Figure 4a). This difference can be reasonably attributed to N fertilization caused pH decline in wheat-rice soils in this area. Whereas, for the subsurface soils (15-30cm), the soil pH was significantly positively correlated with the IN concentration for the wheat-rice land, but not for wetland, though both linear regressions were approximately parallel (Figure 4b), further indicating N-fertilization effects and the effects more significant in surface soils. Consequently, soil pH especially in the surface of the wheat-rice land was significantly lower than in the subsurface and wetland soils (Figure 4c). Carbonate Ca/Mg ratio was the highest in the surface wheat-rice soil. It was significantly higher in the surface wetland soil than that in the subsurface wheat-rice soil, however, there was no significant difference between the subsurface of both land soils and on the wetland profile (Figure 4c), which indicates that magnesium carbonate is more sensitive to the pH change especially in the more acidified surface soils. This re-distribution of Ca/Mg caused by acidification deserves a wider consideration of consequent environment or ecosystem effects. Figure 4 Relationship between soil inorganic nitrogen and pH at different depths (a:0-15cm, b:15-30cm) and corresponding contrast of soil pH (c) and Ca/Mg (d) in wetland and wheat-rice soils in Dapu town Both calcium and magnesium are macronutrient elements supporting terrestrial ecosystems. However, carbonate dissolution and depletion resulting from acid deposition and fertilization undermine the buffering capacity of soils, and will produce damage to the terrestrial ecosystem, as carbonates can retain most heavy metals insoluble and unavailable to plants (Songchao et al., 2019). Once this first barrier to resist soil acidification is exhausted, accelerated divalent base cation losses (Ca and Mg) will occur and followed by rapid soil acidification and ecosystem damage. When soil pH> 7.5, acidification is largely buffered by calcium carbonate; when carbonates depleted to pH < 4.5, non-base cations, such as Al 3+ , Mn 2+ and Fe 3+ , are mobilized and buffer against the acidification (Tian et al., 2015), which will intensify toxicity to many crop plants. Study showed that a transition from base cation buffering to Al 3+ buffering had existed in soils at the global level (Tian et al., 2015). Due to the acid-insensitive region, i.e., higher concentrations of carbonates in the soils, the Taihu watershed has a large buffering capacity and currently remains in the carbonate buffering stage based on our field data, however, the anthropogenic acidification induced carbonate dissolution and calcium/magnesium losses are cumulative and are irreversible. For instance, compared with paddy land soil pH (mean=6.83, Table S1) in 1980s in this watershed, current pH of wheat-rice soil (mean=6.3 from this work) has significantly declined. Furthermore, acidification could deplete soil Ca to such a point that it may become a limiting nutrient in some terrestrial ecosystems (Bérangère et al., 2016). Therefore, the consequent effects on both terrestrial and aquatic ecosystem in the Taihu watershed are calling for a closer investigation. 3.2 Lake sediments Acidification in the watershed and Ca and Mg losses with runoff will definitely produce effects on the lake environment. Analyses of the sediment data showed acid-extracted Ca and Mg had a significantly positive correlation with pH (Figure 5), indicating that in the sediment pH is an important control for carbonate existence. However, compared with watershed soils, carbonate concentrations in the sediment had less variation, which indicates that transportation and transformation of carbonate Ca and Mg in sediments have experienced same geochemical processes from the land to water and were highly homogenous. The acid-extracted Ca/Mg ratio presented a significantly negative correlation with pH (Figure 5), indicating that with the pH increasing, Ca was preferentially bound to carbonate and precipitated over Mg. The statistical analysis showed that sediment pH ranged from 5.1-8.4 for the entire lake and whole profiles, with mean=7.2, which is higher than that of watershed soils, due to the in-lake alkalization, the most important causation to maintain an alkaline environment in the lake (pH≥8) in the past decades (Tao et al., 2016). This is the major reason why sediment carbonates has been increasing during the past decades (Figure 6a and b). Figure 5 Relationship between pH and carbonate Ca or Mg and Ca/Mg in the sediments (Ca and Mg are log-transformed data) The sediment profiles presented a distinctive characteristic that at the depth of around 15cm was an obvious turning point for carbonate Ca, Mg, and sediment pH, below which was a decline trend and above which was an increase trend (Figure 6a-c). The chronological result based on Pb and Cs isotopic dating indicated the depth of 15cm in the sediment corresponding to approximately 40-42 years ago (Cheng et al., 2019), i.e., around the early 1980s, when the impacts by human activities in the watershed became increasingly intensive due to the aggressive economic policy of the entire country. As a result, an abrupt water quality change was observed in Taihu lake from the early 1980s, as well as other major waters in this country (Jianguo et al., 2008). From then on, increasing acid gas emissions have greatly accelerated chemical weathering in the watershed，resulting in base cations (particularly Ca and Mg) losses and delivered to the lake. Meanwhile, the trophic level of Taihu lake rapidly developed into a highly eutrophic state (Hongtao et al., 2012). Thus, an alkaline water environment caused by frequent algae blooms (Tao et al.,2016) rendered Ca 2+ and Mg 2+ delivered to the lake to precipitate with carbonate, resulting in the sedimentation record of an increasing carbonate Ca and Mg trend on the sediment profiles (Figure 6a and b). This bio-geochemical process can be further evidenced by contrasting the sediment profiles in the algae-dominated part in the northwest lake (NW) and the macrophyte-dominated part in the southeast lake (SE) (Figure 1). That is, the sediment pH, acid-extracted Ca and Mg were all higher in NW than those in SE (Figure 6a-c), which implies that algae bloom-induced alkaline environment was more in favor of carbonate precipitation. Different than other parameters, carbonate Ca/Mg ratio presented a general decline trend on the sediment profile from the depth of 20 cm (representing around 1960s) to the surface (Figure d), and presented a higher value in SE than in NW. This different pattern is also associated with the surrounding pH. In the lower sediment pH in SE, more carbonate Mg was released to water than carbonate Ca (Figure 5), resulting in a higher Ca/Mg. However, the overall decline trend below 15cm for pH, acid-extracted Ca and Mg is yet to be explored. Figure 6 Variations on sediment profiles of acid-extract Ca (a) , Mg(b), pH (c) and C/Mg in different lake part (NW: northwest lake, SE: southeast lake) 3.3 Contrast of watershed soils and lake sediments Although acid-extracted Ca and Mg presented a significant correlation in both soils and sediments (p<0.001, Figure 7), their coefficients and variations were quite different. The coefficient between acid-extracted Ca and Mg for the sediment (r=0.944) was more significantly higher than that for the watershed soils (r=0.548). The acid-extracted Ca and Mg in watershed soils are largely parent matrix depended and vary greatly across land uses; while the watershed derived carbonate Ca and Mg has undergone the similar transportation and transformation from land to the lake. Therefore, carbonate Ca and Mg revealed a high homogeneity in the lake sediment. However, in the scatter correlation plots, there were some “outliers” (in the rectangle, Figure 7) for either sediments or soils, characterized by much higher Ca/Mg ratio. By examining these data sites, we found that the soil sites of outliers were in carbonate areas (Figure S1), and sediment sites of outliers were near the west shore or carbonate islands, which indicates the distinctive source characteristic and implies a typical linkage of these base cations between the land and water. Figure 7 Contrast of correlation between acid-extracted Ca and Mg in sediments (a) and soils (b) (Data sites in the rectangle are in or near carbonate rock areas) Further exploring the linkage by contrasting pH, acid-extracted Ca and Mg, and Ca/Mg ratio between the soil and sediment, we found that the lake sediment was a sink for Ca and Mg, weathered in the watershed and transported to the lake. The sediment pH was even higher than carbonate region soils (soil-C) and significantly higher than that in the non- carbonate region soils (soil-NC) (p<0.01, Figure 8a), because of the intensive in-lake alkalinization, particularly in the NW lake (Tao, et.al., 2016). Carbonate Ca in the sediment was only lower than that in the carbonate region soils (soil-C), but significantly higher than that in non- carbonate region soils (soil-NC) (p<0.01, Figure 8b), with a larger area in the watershed. In addition, carbonate Ca and Mg in the NW sediment were significantly higher than those in the SE sediment (p<0.01, Figure 8b and c), because the most inflow rivers transport weathered products to the lake from the northwest watershed (Figure 1). In addition, eutrophication in the NW lake is more intensive than the SE lake, which is in favor of precipitation of Ca and Mg. The lower carbonate Ca/Mg ratio in the sediment than in the soil was likely a reflection of higher solubility of carbonate Mg in waters, and some biogeochemical processes such as organism absorption or uptake of Mg during the lacustrine transportation. However, this re-distribution of base cations from the watershed to lake needs closer studies due to its potential effects on the ecosystem functioning (Bérangère et al., 2016). Conclusions The anthropogenic acidification has greatly accelerated carbonate dissolution and losses in Taihu watershed during the past five decades. Both acid deposition and N fertilization in this region contributed to the acidification and base cation (mainly Ca and Mg) losses. Soils of different land uses are impacted by acidifying effects in this watershed, and the soil of wheat-rice land is most impacted by acidification because of both intensive fertilizer application and acid deposition, while the wetland soil is only impacted by acid rains. Correspondingly, the acid-extract Ca and Mg in wheat-rice soils were significantly lower than those in wetland soils, particularly for the surface soils (0-15cm), which are more susceptible to fertilization and acid rains. Meanwhile, pH of acidification-impacted soils was universally significantly lower than that of less acidification-impacted soils. Even in the same carbonate areas in this watershed, soil pH of N-fertilized vegetable land was lower than that of wetland. Compared with 40 years ago, the average soil pH of the paddy lands in the region overall declined by at least 0.5 pH units. The accelerated carbonates weathering and base cation losses in the past decades were recorded by the lacustrine sedimentary records in Taihu lake. The sediment profile revealed an increasing trend of carbonate C and Mg concentration from the depth of 15cm (around the early 1980s) to surface, and generally higher carbonates in NW (inflow area) sediment than in SE (drainage area), indicating that the lake sediment is a major sink of the base cations transported from the watershed. However, carbonate Ca/Mg ratio had a higher value in less acidified (higher pH) environment in the watershed, but it had a higher value in lower pH environment in the lake sediment, which indicates the different effects of lacustrine ecosystem on the base cation transformation than in the terrestrial ecosystem. Although the soil carbonate system currently plays the major buffering role against the acidification in the watershed due to high carbonates concentration in soils, long-term carbonate dissolution, losses of Ca and Mg, and declined soil pH would pose environmental problems and require more considerations. Furthermore, the potential effects of base cations depletion in the watershed and accumulation in the lake on species diversity and ecosystem functioning remain unclear and need evaluation. In addition, the bio-geochemical processes have changed Ca/Mg ratio between the terrestrial and lacustrine system during their transportation and transformation, and how this re-distribution alters terrestrial and aquatic ecosystem also needs higher resolution researches at both temporal and spatial level. This work helps build more generalized understandings of watershed buffering system against acidification and consequent aquatic effects, and our findings also provide basis to be incorporated into geochemical modelling so as to more accurately predict the linked environmental effect between lands and waters. Declarations Acknowledgement This work was financially supported by the National Natural Science Foundation of China (No. 41871079), and the Open Foundation of State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences (No.SKLECRA2019OFP09 and SKLECRA2021OFP01). Ethical Approval Not applicable Consent to Participate All authors consent to participate in this research. Consent to Publish All authors consent to publish this research in ESPR if accepted. Authors Contributions Yu Tao: Design of the research, field sampling, data analysis, writing original draft Jia Binyang: Field work coordination, data collection and support Wang Rui: Field sampling, sample treatment and measurement Deng Yixiang: Data analysis, manuscript editing Zhuo Xiaoke: Field sampling, sample treatment and measurement，reference editing Cheng Zhonghua: Field sampling, sample treatment and measurement He Chengda: Sample test support, resource support Funding National Natural Science Foundation of China (No. 41871079) Competing Interests The authors have no competing interests Availability of data and materials All data used in this research are available for check from the corresponding author on request of the Editor. References Bérangère A, Leys GE, Likens CE, Johnson JM, Craine B, Lacroix KK, McLauchlan (2016) Natural and anthropogenic drivers of calcium depletion in a northern forest during the last millennium. PNAS 113(25):6934–6938 Chen D, Lan Z, Bai X, Grace JB, Bai Y (2013) Evidence that acidification-induced declines in plant diversity and productivity are mediated by changes in below-ground communities and soil properties in a semi-arid steppe. J Ecol 101(5):1322–1334 Cheng L, Yao S, Xue B, Ling L, Liu J (2019) Long-term change of the assemblages and abundance of Cladocerans in different ecotypes of lake Taihu. J Lake Sci 31(6):1670–1684 Chetelat B, Liu C, Zhao Z, Wang Q, Li S, Li J, Wang B (2008) Geochemistry of the dissolved load of the Changjiang basin rivers: anthropogenic impacts and chemical weathering. Geochim Cosmochim Acta 72(17):4254–4277 Guo L (2007) Doing battle with the green monster of Taihu Lake. Science 317(5842):1166 Guo J, Liu X, Zhang Y, Shen J, Han W, Zhang W, Christie P, Goulding KWT, Vitousek PM, Zhang F (2010) Significant acidification in major Chinese croplands. Science 327(5968):1008–1010 Hongtao D, Ronghua M, Xiaofeng X, Fanxiang K, Shouxuan Z, Weijuan K, Jingyan H, Linlin S (2012) Two-decade reconstruction of algal blooms in china's lake Taihu. Environ Sci Technol 43(10):3522–3528 Jiangsu soil survey office (1995)Jiangsu Soils, China Agriculture Press, Beijing. pp335–338 Kaushal SS, Likens GE, Pace ML, Utz RM, Haq S, Gorman J, Grese M (2018) Freshwater salinization syndrome on a continental scale. PNAS 115(4):574–583 Li Z, Yunpeng Q, Lei C, Yi W, Lingli L, Cong T, Dan CB, Kent OB, Xinmin B, Weijian Z, Shuijin H (2018) Atmospheric CO2 enrichment and reactive nitrogen inputs interactively stimulate soil cation losses and acidification. Environ Sci Technol 52(12):6895–6902 Liang T, Fang L, Cheng L, Xiong F, Li G, Bo W, Shi W, Ming X (2019) Mitigation of soil acidification through changes in soil mineralogy due to long-term fertilization in southern China. CATENA 174:227–234 Lu X, Vitousek PM, Mao Q, Gilliam FS, Luo Y, Turner BL, Zhou G, Mo J (2021) Nitrogen deposition accelerates soil carbon sequestration in tropical forests.PANS.118(16), e2020790118 Mitchell MJ, Likens GE (2011) Watershed sulfur biogeochemistry: shift from atmospheric deposition dominance to climatic regulation. Environ Sci Technol 45(12):5267–5271 Pan Y, Hua M, Liao Q, Xu S, Zhang Y, Zhai H (2018) Distribution properties and time-series comparisons of soil pH-values in Yixing area. Geophysi Geoche Explor 42(4):825–832 (in Chinese with English abstract) Qichao Z, Wim V, Xuejun L, Tianxiang H, Mufan Z, Jianbo S, Fusuo Z (2018) Enhanced acidification in Chinese croplands as derived from element budgets in the period 1980–2010. Sci Total Environ 618(5):1497–1505 Qiquan L, Aiwen L, Xuelian Y, Tianfei D, Yueyue P, Dagang Y, Bin Z, Qi T, Changquan W, Bing L, Xuesong G, Yiding L, Deyong Wu, Qiang X (2020) Soil acidification of the soil profile across Chengdu Plain of China from the 1980s to 2010s. Sci. Total Environ. 698(1), 134320.1-134320.9 Rhodes AL, Newton RM, Pufall A (2001) Influences of Land Use on Water Quality of a Diverse New England Watershed. Environ Sci Technol 35(18):3640–3645 Shi K, Zhang Y, Xu H, Zhu G, Qin B, Huang C, Liu X, Zhou Y, Lv H (2015) Long-term satellite observations of microcystin concentrations in lake Taihu during cyanobacterial bloom periods. Environ Sci Technol 10(11):6448–6456 Slessarev EW, Lin Y, Bingham NL, Johnson JE, Dai Y, Schimel JP, Chadwick OA (2016) Water balance creates a threshold in soil pH at the global scale. Nature 540:567–569 Songchao C, Zongzheng L, Richard W, Ganlin Z, Yin Z, Hongfen T, Bifeng H, Dominique A, Zhou S (2019) A high-resolution map of soil pH in China made by hybrid modelling of sparse soil data and environmental covariates and its implications for pollution. Sci Total Environ 655:273–283 Sulpis O, Boudreau BP, Mucci A, Jenkins C, Key RM (2018) Current CaCO 3 dissolution at the seafloor caused by anthropogenic CO 2 . PANS 115(46):11700–11705 Sulpis O, Jeansson E, Dinauer A, Lauvset SK, Middelburg JJ (2021) Calcium carbonate dissolution patterns in the ocean. Nat Geosci 14(7):423–428 Tao Y, Qiujin X, Chengda H, Haibing C, Dan D, Fengchang W, Wei M (2016) Long Term Trends in Acid Neutralizing Capacity under Increasing Acidic Deposition: A Special Example of Eutrophic Taihu Lake, China. Environ Sci Technol 50(23):12660–12668 Tessier AP, Campbell PGC, Bisson MX (1979) Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 51(7):844–851 Tian D, Niu S (2015) A global analysis of soil acidification caused by nitrogen addition. Environ Res Lett 10(2):1714–1721 Wang Q, Yu H, Liu J, Li F (2018) Attribution of soil acidification in a large scale region: artificial intelligence approach application. Soil Sci Soc Am J 82:772–782 Weyhenmeyer GA, Hartmann J, Hessen DO, Kopáek J, Zechmeister T (2019) Widespread diminishing anthropogenic effects on calcium in freshwaters. Sci Rep 9(1):1–10 Yang Y, Ji C, Ma W, Wang S, Wang S, Huan W, Mohamma A, Robinson D, Smith P (2012) Significant soil acidification across northern China's grasslands during 1980s-2000s. Glob Change Biol 18:2292–2300 Yu T, Dai D, Lei K, He C, Cong H, Fu G, Xiu Q, Sun F, Wu F (2018) δ15N and Nutrient Stoichiometry of Water, Aquatic Organisms and Environmental Implications in Taihu lake. China Environ Pollut 237(6):166–173 Yu T, Zhang Y, Wu F, Meng W (2013) Six-Decade Change in Water Chemistry of Large Freshwater Lake Taihu, China. Environ Sci Technol 47(16):9093–9101 Supplementary Files Supplementarymaterial.docx Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Minor Revision 07 Jun, 2022 Reviewers agreed at journal 21 May, 2022 Reviews received at journal 15 May, 2022 Reviewers invited by journal 15 May, 2022 Editor invited by journal 10 May, 2022 Editor assigned by journal 25 Apr, 2022 First submitted to journal 13 Apr, 2022 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies 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-1556696","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":106063039,"identity":"eccf2f15-e618-4fbd-b947-6c37ef4945c8","order_by":0,"name":"Yu Tao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA0UlEQVRIiWNgGAWjYNACgxo5+/YGhgNEKmcG4opjxgY8B0jScoY5cYNEArFOupF/8MPHNjbG7ZLPHx4uqGGQ5xcjYJnBjWRmyZltMsyWs3MMDs84xmA4czYB64BaGKR529jYGG7nMBzmYWNIMLhNWAvzb942Zh6Gm8cfHOb5R5wWNmmeM8wSBjcYDA7zthGhRfLMYzPLGRXHDCR7gH7h7ZMg7Be+44mPb3wwqKnvZz/++DPPNxt5fmkCWhQOoPIl8CsHAfkGwmpGwSgYBaNgpAMA+lNE5RWmo8QAAAAASUVORK5CYII=","orcid":"","institution":"Chinese Research Academy of Environmental Sciences","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Tao","suffix":""},{"id":106063040,"identity":"b40f9b1c-909f-4ba2-9808-3b0a73ef64ee","order_by":1,"name":"Jia Binyang","email":"","orcid":"","institution":"CRAES: Chinese Research Academy of Environmental 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University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Zhuo","middleName":"","lastName":"Xiaoke","suffix":""},{"id":106063044,"identity":"63e47a40-da2f-4cb1-af01-8338af24ded4","order_by":5,"name":"Cheng Zhonghua","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Cheng","middleName":"","lastName":"Zhonghua","suffix":""},{"id":106063045,"identity":"d5d49784-b40e-43db-8800-39f6476aa209","order_by":6,"name":"He Chengda","email":"","orcid":"","institution":"Yangzhou University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"He","middleName":"","lastName":"Chengda","suffix":""}],"badges":[],"createdAt":"2022-04-14 06:25:06","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-1556696/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-1556696/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":21583604,"identity":"5b131277-2aaf-443f-94bb-2e140ac420f6","added_by":"auto","created_at":"2022-05-17 19:25:03","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":160409,"visible":true,"origin":"","legend":"\u003cp\u003eThe river networks upstream of Taihu lake and soil sampling sites in different land uses and sediment sites in different lake part (Dash square indicates Dapu town near the lake, in which sampled soils were regarded to have identical matric for contrast of acidifying effect of different “treatments”)\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/5519b1716072bb97f2d44bc6.png"},{"id":21583184,"identity":"834c23db-ebc4-49c9-b4a2-04ca8d1ce21e","added_by":"auto","created_at":"2022-05-17 19:20:03","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":398468,"visible":true,"origin":"","legend":"\u003cp\u003eCorrelation between soil pH and acid-exacted Ca (a), Mg (b) and Ca/Mg ratio (c) in different land uses\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/3bdd9fcac255892ba647e2e5.png"},{"id":21583601,"identity":"d7542cdd-a854-4500-8367-44c7a7942252","added_by":"auto","created_at":"2022-05-17 19:25:03","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":326876,"visible":true,"origin":"","legend":"\u003cp\u003eConstras of soil pH, acid-extracted Ca and Mg and Ca/Mg at different depths of different land uses (y-axis for carbonate concentrations is normalized coordinate)\u0026nbsp;\u0026nbsp;\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/56b51f3063581bfad958704d.png"},{"id":21583602,"identity":"d288df19-f949-4271-80e0-57263371fceb","added_by":"auto","created_at":"2022-05-17 19:25:03","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":376633,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between soil inorganic nitrogen and pH at different depths (a:0-15cm,\u0026nbsp;b:15-30cm) and corresponding contrast of soil pH (c) and Ca/Mg (d) in wetland and wheat-rice soils in Dapu town\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/8283ad2cac3ae44ff64eb72d.png"},{"id":21584155,"identity":"d8169954-1674-461c-8b10-d50d89046b23","added_by":"auto","created_at":"2022-05-17 19:30:03","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":451798,"visible":true,"origin":"","legend":"\u003cp\u003eRelationship between pH and carbonate Ca or Mg and Ca/Mg in the sediments (Ca and Mg are log-transformed data)\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/106746ced7a9be73e97f6a2b.png"},{"id":21584156,"identity":"6434e044-edd5-4336-ac9b-ea968dd1f9b8","added_by":"auto","created_at":"2022-05-17 19:30:03","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":314679,"visible":true,"origin":"","legend":"\u003cp\u003eVariations on sediment profiles of acid-extract Ca (a) , Mg(b), pH (c) and C/Mg in different lake part (NW: northwest lake, SE: southeast lake)\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/1f62357b2585a060df9781bf.png"},{"id":21583186,"identity":"014a1f4e-f760-48c8-ab16-b37273425573","added_by":"auto","created_at":"2022-05-17 19:20:03","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":273415,"visible":true,"origin":"","legend":"\u003cp\u003eContrast of correlation between acid-extracted Ca and Mg in sediments (a) and soils (b) (Data sites in the rectangle are in or near carbonate rock areas)\u003c/p\u003e\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/49832729e65b9c224944fa14.png"},{"id":21583190,"identity":"9fb4e44d-043b-42c7-9eae-90c77512bba7","added_by":"auto","created_at":"2022-05-17 19:20:03","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":348286,"visible":true,"origin":"","legend":"\u003cp\u003eParameter contrast between sediments and soils of different layer average (y-axis for carbonate concentrations is normalized coordinate. NW: northwest lake, SE: southeast lake; Soil-C: soil in carbonate area, Soil-NC: soil in non-carbonate area)\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/5468acdc85779e0064fa4039.png"},{"id":21584157,"identity":"982fb73b-3747-4e5d-b65e-49003a004549","added_by":"auto","created_at":"2022-05-17 19:30:06","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":239025,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/8c1a888b-8567-44ec-84bc-7596cdd3eaf4.pdf"},{"id":21583192,"identity":"06e8d1e7-419b-485f-af3a-be08f6319dc4","added_by":"auto","created_at":"2022-05-17 19:20:03","extension":"docx","order_by":5,"title":"","display":"","copyAsset":false,"role":"supplement","size":388334,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterial.docx","url":"https://assets-eu.researchsquare.com/files/rs-1556696/v1/209ab05e180943ab0006e4d3.docx"}],"financialInterests":"","formattedTitle":"Accelerated Carbonates Dissolution Caused by Anthropogenic Acidification - Contrast of Watershed Soils to Lake Sediments in Taihu Region, China","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eCalcium (Ca) and magnesium (Mg) are abundant elements in the earth surface system and are necessary macronutrients for the human and other living beings. These base cations are important in the maintaining of terrestrial and aquatic ecosystems, and their existence and concentration can regulate or alter species distribution (Weyhenmeyer et al., 2019) and ecosystem change (B\u0026eacute;rang\u0026egrave;re et al., 2016). In the natural system, these rock-derived elements retain dynamic balance between terrestrial and water systems, however, this balance has been changed by the increasing human disturbance. A typical trend of this change is the significant increase in water hardness or alkalinity at the regional (Yu et al., 2013) or continental scale (Kaushal et al., 2018). One of the important driving forces to accelerate the base cation losses from lands to waters is human-induced acidification, generally caused by acidic gas emissions (Yu et al., 2013) and nitrogen fertilizer applications (Liang et al., 2019). Although soils acidify under natural conditions very slowly, usually over hundreds to millions of years, this process has been greatly accelerated by human activities (Guo et al., 2010). Atmospheric deposition caused acidification, commencing in Europe and eastern North America in the middle of the 20th century, also known as acid rain, has caused a series of environment problems and caused worldwide concerns (B\u0026eacute;rang\u0026egrave;re et al., 2016). For example, atmospheric deposition of sulfide has been the dominant factor causing widespread and deleterious impacts on aquatic and terrestrial ecosystems (Mitchell and Linkens, 2011), and global land has received more than 50 kg ha\u003csup\u003e\u0026minus;1\u003c/sup\u003e accumulated N deposition during 2000\u0026ndash;2010, which has been documented as the main causation of soil acidification in terrestrial ecosystems (Tian et al., 2015). In addition, long-term N enrichment via fertilization in soils is another factor causing environment acidification (Guo et al., 2010). This is particularly true in China as N fertilizer consumption has rapidly increased to maintain or increase crop production. The national average N input was up to 311 kg N/ha/yr in 2010 in China, much higher than the world average, and overuse of N fertilizer contributes substantially to regional soil acidification in this country (Qichao et al., 2018).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u0026nbsp;Acidification has resulted in profound environment problems and ecosystem damages. In oceans, acidification-induced carbonate dissolution could produce substantial consequences to the ecology of calcifiers (Sulpis et al., 2018), as carbonates such as calcite, constitute the shells of most coccolithophores and planktonic foraminifera (Sulpis et al., 2021). In terrestrial systems, acidification can result in soil quality degradation and soil environmental damage by accelerating lossess and depletion of soil nutrients, e.g., Ca\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e+\u003c/sup\u003e, Mg\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e (Slessarev et al., 2016). Additionally, it can mobilize toxic metals such as Al\u003csup\u003e3+ \u003c/sup\u003eand Mn\u003csup\u003e2+\u003c/sup\u003e and elevate their available concentrations in the soil solution, thus resulting in deleterious impacts on both aquatic and terrestrial ecosystems (Mitchell and Likens, 2011), and even affecting public health (Wang et al., 2018). Furthermore, serious soil acidification may induce the destruction of carbon balance in terrestrial ecosystems with large losses of soil carbon (Yang et al., 2012), and may be a significant threat to species diversity and terrestrial ecosystem functioning (Chen et al., 2013).\u003c/p\u003e\n\u003cp\u003eRock derived base cations (particularly Ca\u003csup\u003e2+\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e) are critically important in buffering soil acidification at the early stage (Yang et al., 2012). When the environment pH is higher than 7.5, soil acidification is largely buffered by calcium carbonate; when pH at the range from 4.5 to 7.5, the acidification process is mostly buffered by base cations, such as exchangeable Ca\u003csup\u003e2+\u003c/sup\u003e, Mg\u003csup\u003e2+\u003c/sup\u003e, K\u003csup\u003e+\u003c/sup\u003e, etc. (Tian at al., 2015). However, with the development of acidification, depletion of carbonates or base cations and a series of consequent environment problems are expected. Once surrounding pH \u0026lt; 4.5，these base cations become severely deficient, and non-base cations (Al\u003csup\u003e3+\u003c/sup\u003e, Fe\u003csup\u003e3+\u003c/sup\u003e) are mobilized to buffer against the acidification. It is reported that global soils may have shifted from base cation buffering to Al\u003csup\u003e3+\u003c/sup\u003e buffering due to anthropogenic acidification (Tian at al., 2015). Base cation depletion will in turn cause further ecosystem problem. A recent study showed that, in the northeastern United States, forest growth declined along with decreased soil calcium availability, indicating that the regional acid rain had depleted soil Ca to the point where it may be a limiting nutrient (B\u0026eacute;rang\u0026egrave;re et al., 2016).\u003c/p\u003e\n\u003cp\u003eChina is the third major acid rain region on the globe after Europe and America, and Taihu region is one of the most serious acid rain areas in China, with the average atmospheric deposition pH\u0026lt;5 during 2011-2015 (Tao et al., 2016). In addition, intensive N fertilizer applications (515 kg N/ha/yr) in this region (Qichao et al., 2018) even exacerbated local soil acidification. Consequently, in the past decades, the hardness (Ca\u003csup\u003e2+\u003c/sup\u003eand Mg\u003csup\u003e2+\u003c/sup\u003e) of Taihu lake water increased by three folds (Yu et al., 2013) due to accelerated chemical weathering caused by acidification in the watershed. The water quality and eutrophication issues in the Taihu watershed have drawn worldwide attentions and have been well documented (Guo et al., 2007). However, carbonate dissolution resulting from acid deposition and nitrogen fertilization in the watershed so far has been rarely reported, most likely due to the \u0026ldquo;acid\u0026ndash;insensitive\u0026rdquo; characteristic of this region, i.e., an abundance of carbonates distribution in the watershed (Chetelat et al., 2008). However, the carbonate dissolution, consequent base cation losses and the lake responses deserve a closer attention, as these geochemical processes will likely produce profound, if not immediate, and irreversible effects on the both terrestrial and aquatic ecosystems. This study aims to (1) characterize the distribution of calcium and magnesium carbonates in soils of different land uses under the acidification background in Taihu watershed,（2）elucidate carbonates distribution on the profile of lake sediments, and（3）explore the linkage between the terrestrial base cation loss and lake sedimentation. This work is expected to provide basis for the quantitative modelling of carbonate dissolution and subsequent evaluation of the ecosystem effects in the acidification-impacted regions.\u003c/p\u003e"},{"header":"2. Material And Methods ","content":"\u003cp\u003e2.1 Site Delineation\u003c/p\u003e\n\u003cp\u003eThe Taihu watershed is located in the downstream of the Yangtze River. It is one of the most economically developed and most densely populated areas in China, and it has been the breadbasket through the long Chinese history. Our study area involved the upstream river systems in the Taihu watershed and Taihu lake (Figure 1). The general topography of the Taihu watershed is characterized by hilly areas in the northwest and southwest to the lake, where river networks in this watershed originate and discharge into Taihu lake, thus composing the major linkage between the land and water environment through the river flux delivery (Figure1). Downstream of the hilly areas is the alluvial plain and Quaternary deposits, where the highly mature soils have undergone intensive weathering and leaching. Therefore, this work focused on the soils in the upstream drainage systems in the watershed to explore the linkage of the carbonate dissolution and sedimentation between the land and the lake.\u003c/p\u003e\n\u003cp\u003eThe matrices in the Taihu watershed are dominated by clastic rocks and carbonates (Chetelat et al., 2008), and the soil type in this region mainly consists of the yellow-brown soil, red soil, and paddy soil. Due to carbonates distribution in this watershed, considerable carbonate concentration is observed in local soils, which plays a major buffer to the acidification resulting from acid rains and nitrogen fertilization. According to the document, the concentration of calcium carbonate in various soils in Jiangsu province (a major area in the upstream of the Taihu watershed) ranged from 0.4-100g/kg (by gasometric method), of which the soil area with calcium carbonate\u0026lt;10g/kg accounted for approximate 50% of the total soil area (Jiangsu soil survey office, 1995). Carbonate rocks also appear in the Xishan Island in Taihu lake (Figure 1), where the carbonates constitute the main part of the hills and the carst caves also exist, which is a famous tourism resort. Taihu lake is characterized with two distinctive lake parts, i.e., the algae-dominated part in the northwest lake (NW), where surrounding pH is higher due to algae bloom effects, and the macrophyte-dominated part in the southeast lake (SE) (Figure 1), where the environment pH is relatively lower than the NW part. The environmental differences between the two lake parts were documented in our previous work (Yu et al., 2018).\u003c/p\u003e\n\u003cp\u003eThe Taihu region, located in the Yangtze Delta, has long been a breadbasket through the Chinese history, and it is one of the most economically developed areas in China, with the highest population density and high urbanization rate in this country. Due to the intensive anthropogenic disturbance, the Taihu watershed and the lake has undergone remarkable environmental changes in the past decades (Shi et al., 2015). One of the environmental concerns was acidification caused by both acid deposition and nitrogen fertilization application. This region is one of the most serious acid rain areas in China due to acidic gas emissions (Tao et al., 2016); on the other hand, the nitrogen fertilizer application in the local farmland (515 kg N/ha/yr) was much higher than the national average (Qichao et al., 2018). As a consequence, the losses of the terrestrial base cations and significantly increased hardness (Ca \u003csup\u003e2+\u003c/sup\u003e+Mg\u003csup\u003e2+\u003c/sup\u003e) of the lake water during past decades have been greatly accelerated (Yu, et al., 2013) and will likely produce effects on the aquatic ecosystem (Weyhenmeyer et al., 2019). However, this issue so far has received much less attention than water pollution and eutrophication of this famous lake.\u003c/p\u003e\n\u003cp\u003e2.2 Sampling and sample pre-treatment\u003c/p\u003e\n\u003cp\u003eThe river systems, the lake, and all watershed soil and lake sediment sampling sites in this study are shown in Figure 1. The sampled carbonate sites in the watershed and small islands with carbonate rocks nearby Xishan island (north to Xishan island) in Taihu lake are illustrated in Figure S1. All Soil and sediment samples were taken in the six field investigations during 2017-2019, with 20% sampling sites repeated to check the reproducibility of the tests. The soil sites were distributed along the two major upstream river systems in the northwest of Taihu lake (Figure 1) so as to explore the linkage between the land and the lake. The soil samples were taken from four land uses, i.e., the dominant crop land or wheat-paddy rotation land soil and vegetable land soil, which are impacted by both chemical N fertilizer addition and acid deposition; wetland and forest land soil, both of which are only impacted by the acid deposition. All soil samples were taken with a soil corer sampler with a diameter of 5cm, and the soil column was segmented into 3cm sections from the surface to bottom in situ. Soil sections were preserved at around 4℃ until further processing in the laboratory.\u003c/p\u003e\n\u003cp\u003eFigure 1 The river networks upstream of Taihu lake and soil sampling sites in different land uses and sediment sites in different lake part (Dash square indicates Dapu town near the lake, in which sampled soils were regarded to have identical matric for contrast of acidifying effect of different \u0026ldquo;treatments\u0026rdquo;)\u003c/p\u003e\n\u003cp\u003eThe lake sediment sites, designed to reflect the entire lake character, were located in the two distinctive parts of the lake-the northwest (NW) and the southeast (SE) lake area, with 9 sites at the representative lake bays and the open lake in the NW part and 4 in the SE part (Figure 1). The sediment samples were taken using a gravity core sampler with a diameter of 10 cm and length of 50 cm. Each sediment core was sliced into 2 cm sections from the surface to bottom in situ to explore the profile chronological characteristics. All segmented sediments were preserved at around 4℃ until further processing in the laboratory. In the laboratory, all soil and sediment samples were first freeze-dried and then ground and sieved with a 100-mesh sieve to obtain the \u0026lt;63 \u0026mu;m fraction, which was prepared for parameter measurements.\u003c/p\u003e\n\u003cp\u003e2.3 Sample measurement and quality control\u003c/p\u003e\n\u003cp\u003eFor the pH measurement of each soil and sediment sample, the extracted solution was first prepared by adding Milli-Q water to the sieved soil or sediment sample (mass ratio of water/soil or sediment= 5:1). The mixture was then mechanically shaken at 250 r/min at 25℃ for 24 h. After shaking, the overlaying solution was measured for pH using HACH (HQ30d) multi-functional water quality parameter instrument. The acid-extracted Ca and Mg of soil and sediment samples were extracted using 1M NaAc adjusted to pH =5.0 with acetic acid (HAc), which is regarded as carbonate combined species of Ca or Mg (Tessier et al., 1979). Then the extracted supernatant was analyzed for Ca and Mg concentration using the atomic absorption spectroscopy method (AA240FS/GTA120). Nitrogen species (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e, NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e and total nitrogen) of soil samples were analyzed using spectrophotometry (Shimadzu, UV-1800).\u003c/p\u003e\n\u003cp\u003eParallel tests and the reference sample (GSD-10) were used for the analytical quality assurance in the sample processing and test. The relative standard deviation (RSD) of replicated tests was \u0026lt;25% and the recovery of the reference sample tests was 87-112% (for Ca) and 83-106% (for Mg).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;2.4 Data manipulation\u003c/p\u003e\n\u003cp\u003eLogarithm transform (for correlation analysis) or normalization (for column plots) of the acid-extracted Ca/Mg raw data was utilized in the graphic presentation to eliminate large variance and make the results comparable at the same scale. The column plot was used to summarize and contrast the distribution of measured results. Data distribution was tested prior to the statistical analysis/calculation to select the appropriate parametric/non-parametric test. The Pearson coefficient was calculated based on accepted normal distribution assumption otherwise nonparametric coefficient was calculated in the correlation analysis. Statistical comparison was based on independent-samples t-test (for two variables) or One-Way ANOVA (for three or more variables). Linear regression was used to explain how the observed factor (variable) affected the target variable. A significance level of 0.05 was used for the statistical testing. All data calculations, statistical analyses, and mapping were performed with Origin 9.3, SPSS 23, and ArcGIS 10.\u003c/p\u003e"},{"header":"3. Results And Discussion","content":"\u003cp\u003eIn this study, acid-extracted Ca and Mg and relevant parameters such as pH and acid-extracted Ca/Mg ratio of all soils and sediments were highlighted to elucidate how the acidification impacted carbonate bound Ca or Mg in different land uses and in the lake sediment. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e3.1 Watershed soils\u003c/p\u003e\n\u003cp\u003eOur field data showed that both calcium carbonate and magnesium carbonate concentrations of the four land use soils presented a significantly positive correlation to soil pH (Figure 2a and b), indicating that pH is an important regulator of soil carbonate concentrations. This positive correlation between pH and acid-extracted Ca or Mg also implies higher calcareous soils having stronger buffering capacity against acidification, and pH decreasing with calcium and magnesium carbonates losses at the watershed scale. A negative correlation between pH and Ca/Mg ratio was observed in all land use soils (Figure 2c), which indicates that at the same pH condition, magnesium carbonate is more likely to dissolve and run off than calcium carbonate. Figure 2 also showed Carbonate Ca or Mg and Ca/Mg having the least variations in wheat-rice land soils, and the largest variations in forest soils, and we supposed that this variation pattern was largely associated with the acidified extent.\u003c/p\u003e\n\u003cp\u003eFigure 2 \u0026nbsp;Correlation between soil pH and acid-exacted Ca (a), Mg (b) and Ca/Mg ratio (c) in different land uses\u003c/p\u003e\n\u003cp\u003eThe examined parameters on soil profiles can further explain how acidification affected their variations in different land use soils and at different depths. The surface soils are more susceptible to acidification. pH of all soils ranged from 4.3 to 8.5, with the average of 6.6 \u0026plusmn; 0.8. Whereas the surface soil (0-15cm) of four land uses had significantly different pH, and the wheat-rice soil pH (mean=6.34) and forest soil pH (mean=6.27) were significant lower than vegetable and wetland soils (p\u0026lt;0.05), while there was no significant difference between wheat-rice soil pH and forest soil pH, and between vegetable and wetland soils (Figure 3a). The wheat-rice soils having the lowest pH in this watershed is reasonably well understood as the wheat-rice land simultaneously received two acidifying processes, i.e., intensive N fertilization and acid deposition in this region. Furthermore, there existed an observable pH gradient down the soil depth in the vegetable and wheat-rice soil (Figure 3a), indicating N fertilization played a significant role in the acidification in contrast to forest and wetland soil profiles. Previous study using 11 year of continuous N addition experiment showed that excess N inputs significantly decreased soil pH, typically with the topsoil pH lower than subsoil pH (Lu et al., 2021), which is in good agreement with our field findings. It seems unusual that the forest soils, without impacts of fertilization, had the similar surface soil pH to the wheat-rice soil, and we attribute this to two factors. On the one hand, the forest lands are generally located in the upstream hilly areas in the watershed, where the bed rocks, based on our field investigation, are mostly silicates and their weathered products are acidic. On the other hand, eluviation is relatively intensive in hilly areas, which caused further lower soil pH with the losses of cations (Pan et al., 2018). Consistent with the positive correlation between soil pH and carbonates (Figure 2), the acid-extracted calcium and magnesium concentrations of the surface soils (0-15cm) were the lowest in the wheat-rice soil (Figure 3b and c), which is most acidified in the four land use soils due to dual impacts from acid deposition and intensive N fertilization. And the carbonate concentration was the highest in the wetland topsoils (Figure 3b and c), which are generally located in the plain areas and only impacted by acid deposition but no fertilization compared with wheat-rice and vegetable lands. It is noticeable that carbonate Ca and Mg were higher in the forest land than in the wheat-rice land, especially for the topsoils (Figure 3b and c), which is due to the harvest removal of base cations in wheat-rice lands, causing further decline in these cations (Qichao et al., 2018). This also explained why wetland soils had the highest carbonate Ca and Mg concentrations.\u0026nbsp;\u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 3\u0026nbsp; Constras of soil pH, acid-extracted Ca and Mg and Ca/Mg at different depths of different land uses (y-axis for carbonate concentrations is normalized coordinate)\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eBedrock weathering has strong controls over the concentration of Ca and Mg in the watershed soils, which in turn affects the Ca/Mg ratio of the soil (Rhodes et al., 2001). In the Taihu watershed, soils in carbonate areas (Figure S1) are characterized by the highest Ca and Mg concentration and Ca/Mg ratio. In addition, acidification exerts considerable impacts on Ca/Mg ratio as indicated in Figure 2c. Soil profile of the wheat-rice land, with a higher acidified degree in the topsoil than in the subsoil (Figure 3a), further illustrated that Ca/Mg ratio presented a distinct decline down the soil depth (Figure 3d), indicating preferential dissolution and loss of magnesium carbonate over calcium carbonate at the same pH surroundings.\u0026nbsp;\u0026nbsp;\u0026nbsp; \u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eSoil pH and carbonates are parent material dependent (Qiquan et al., 2020). In the carbonate areas in this watershed (Figure S1), the surface (0-15cm) soil pH and acid-extracted Ca or Mg were significantly higher than in the non-carbonate areas, and even the vegetable soils in the carbonate region, impacted by both N fertilization and acid deposition, had higher pH and carbonate concentrations than those in non-carbonate regions. For example, the mean pH of 7.62 in carbonate surface soils was significantly higher than that in other soils (mean pH=6.37, p\u0026lt;0.01); and the mean acid-extracted Ca and Mg concentrations in the surface soil from carbonate areas were 1993.5 mg/kg and 183.8 mg/kg, respectively; while in the non-carbonate areas they were 284.3 mg/kg and 38.2 mg/kg, respectively.\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn spite of parent material control, previous field experimental result suggested that proton produced by nitrification played a dominant role in acidifying soil and promoting cation release (Li et al., 2018), and this process can be expressed by NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e+ 2O\u003csub\u003e2\u003c/sub\u003e =NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e-\u003c/sup\u003e + H\u003csub\u003e2\u003c/sub\u003eO + 2H\u003csup\u003e+\u003c/sup\u003e. A previous study identified a critical level of 200 kg ha\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csup\u003e1\u003c/sup\u003e yr\u003csup\u003e\u0026minus;\u003c/sup\u003e\u003csup\u003e1 \u003c/sup\u003efor N fertilizer use, above which soil acidification would be promoted (Qiquan et al., 2020). Our field observations confirmed these mechanisms. In the Taihu watershed, the average N inputs (515 kg /ha/yr) in the farmlands are much higher than that (Qichao et al., 2018), resulting in more intensive acidification. Our findings highlighted that, even in the carbonate areas, acidification by N fertilization was significant. In the Wu Xing carbonate area (Figure S1), for example, the average pH (=7.77\u0026plusmn;0.10) of the vegetable topsoil was significantly lower than that of the wetland (pH=8.26\u0026plusmn;0.14, p\u0026lt;0.01, Figure S2). The difference of 0.49 pH units can be ascribed to N fertilization in the vegetable land, because both soils received the identical acid deposition. In addition, the similar soil pH of hilly carbonate areas to the vegetable soil (Figure S2) again indicated the impact of eluviation on the soil pH even in carbonate regions.\u003c/p\u003e\n\u003cp\u003eTo further identify the role of acid deposition and nitrogen fertilization in the soil acidification and base cation losses, we focused on the field of Dapu town (indicated by the dashed square area in Figure 1) near Taihu lake, where the soil matrices of different land uses are identical. Therefore, we can regard the soil of different land uses as different \u0026ldquo;acidification treatments\u0026rdquo;, i.e., only acid deposition in wetland soils and acid deposition + N fertilization in wheat-rice soils. By examining the relationship between nitrogen species and soil pH, we found that ammonium (NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N) or nitrate (NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N) had a correlation to soil pH, but not total nitrogen. Thus, we used NH\u003csub\u003e4\u003c/sub\u003e\u003csup\u003e+\u003c/sup\u003e-N+NO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e-N (inorganic nitrogen, IN) to explore the soil acidification effect. The result showed that, for the topsoil (0-15cm), the soil pH was significantly positively correlated with the IN concentration for both wheat-rice land and wetland, and the linear regressions for both land soils were nearly parallel, with an intercept difference of 0.56 (Figure 4a). This difference can be reasonably attributed to N fertilization caused pH decline in wheat-rice soils in this area. Whereas, for the subsurface soils (15-30cm), the soil pH was significantly positively correlated with the IN concentration for the wheat-rice land, but not for wetland, though both linear regressions were approximately parallel (Figure 4b), further indicating N-fertilization effects and the effects more significant in surface soils. Consequently, soil pH especially in the surface of the wheat-rice land was significantly lower than in the subsurface and wetland soils (Figure 4c). Carbonate Ca/Mg ratio was the highest in the surface wheat-rice soil. It was significantly higher in the surface wetland soil than that in the subsurface wheat-rice soil, however, there was no significant difference between the subsurface of both land soils and on the wetland profile (Figure 4c), which indicates that magnesium carbonate is more sensitive to the pH change especially in the more acidified surface soils. This re-distribution of Ca/Mg caused by acidification deserves a wider consideration of consequent environment or ecosystem effects. \u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 4 Relationship between soil inorganic nitrogen and pH at different depths (a:0-15cm, \u0026nbsp;b:15-30cm) and corresponding contrast of soil pH (c) and Ca/Mg (d) in wetland and wheat-rice soils in Dapu town\u003c/p\u003e\n\u003cp\u003eBoth calcium and magnesium are macronutrient elements supporting terrestrial ecosystems. However, carbonate dissolution and depletion resulting from acid deposition and fertilization undermine the buffering capacity of soils, and will produce damage to the terrestrial ecosystem, as carbonates can retain most heavy metals insoluble and unavailable to plants (Songchao et al., 2019). Once this first barrier to resist soil acidification is exhausted, accelerated divalent base cation losses (Ca and Mg) will occur and followed by rapid soil acidification and ecosystem damage. When soil pH\u0026gt; 7.5, acidification is largely buffered by calcium carbonate; when carbonates depleted to pH \u0026lt; 4.5, non-base cations, such as Al\u003csup\u003e3+\u003c/sup\u003e, Mn\u003csup\u003e2+\u003c/sup\u003e and Fe\u003csup\u003e3+\u003c/sup\u003e, are mobilized and buffer against the acidification (Tian et al., 2015), which will intensify toxicity to many crop plants. Study showed that a transition from base cation buffering to Al\u003csup\u003e3+\u003c/sup\u003e buffering had existed in soils at the global level (Tian et al., 2015). Due to the acid-insensitive region, i.e., higher concentrations of carbonates in the soils, the Taihu watershed has a large buffering capacity and currently remains in the carbonate buffering stage based on our field data, however, the anthropogenic acidification induced carbonate dissolution and calcium/magnesium losses are cumulative and are irreversible. For instance, compared with paddy land soil pH (mean=6.83, Table S1) in 1980s in this watershed, current pH of wheat-rice soil (mean=6.3 from this work) has significantly declined. Furthermore, acidification could deplete soil Ca to such a point that it may become a limiting nutrient in some terrestrial ecosystems (B\u0026eacute;rang\u0026egrave;re et al., 2016). Therefore, the consequent effects on both terrestrial and aquatic ecosystem in the Taihu watershed are calling for a closer investigation.\u003c/p\u003e\n\u003cp\u003e3.2 Lake sediments\u0026nbsp;\u0026nbsp;\u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; Acidification in the watershed and Ca and Mg losses with runoff will definitely produce effects on the lake environment. Analyses of the sediment data showed acid-extracted Ca and Mg had a significantly positive correlation with pH (Figure 5), indicating that in the sediment pH is an important control for carbonate existence. However, compared with watershed soils, carbonate concentrations in the sediment had less variation, which indicates that transportation and transformation of carbonate Ca and Mg in sediments have experienced same geochemical processes from the land to water and were highly homogenous. The acid-extracted Ca/Mg ratio presented a significantly negative correlation with pH (Figure 5), indicating that with the pH increasing, Ca was preferentially bound to carbonate and precipitated over Mg.\u0026nbsp;\u0026nbsp; \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe statistical analysis showed that sediment pH ranged from 5.1-8.4 for the entire lake and whole profiles, with mean=7.2, which is higher than that of watershed soils, due to the in-lake alkalization, the most important causation to maintain an alkaline environment in the lake (pH\u0026ge;8) in the past decades (Tao et al., 2016). This is the major reason why sediment carbonates has been increasing during the past decades (Figure 6a and b).\u003c/p\u003e\n\u003cp\u003eFigure 5 \u0026nbsp;Relationship between pH and carbonate Ca or Mg and Ca/Mg in the sediments (Ca and Mg are log-transformed data)\u003c/p\u003e\n\u003cp\u003eThe sediment profiles presented a distinctive characteristic that at the depth of around 15cm was an obvious turning point for carbonate Ca, Mg, and sediment pH, below which was a decline trend and above which was an increase trend (Figure 6a-c). The chronological result based on Pb and Cs isotopic dating indicated the depth of 15cm in the sediment corresponding to approximately 40-42\u0026nbsp; years ago (Cheng et al., 2019), i.e., around the early 1980s, when the impacts by human activities in the watershed became increasingly intensive due to the aggressive economic policy of the entire country. As a result, an abrupt water quality change was observed in Taihu lake from the early 1980s, as well as other major waters in this country (Jianguo et al., 2008). From then on, increasing acid gas emissions have greatly accelerated chemical weathering in the watershed，resulting in base cations (particularly Ca and Mg) losses and delivered to the lake. Meanwhile, the trophic level of Taihu lake rapidly developed into a highly eutrophic state (Hongtao et al., 2012). Thus, an alkaline water environment caused by frequent algae blooms (Tao et al.,2016) rendered Ca\u003csup\u003e2+\u003c/sup\u003e and Mg\u003csup\u003e2+\u003c/sup\u003e delivered to the lake to precipitate with carbonate, resulting in the sedimentation record of an increasing carbonate Ca and Mg trend on the sediment profiles (Figure 6a and b). This bio-geochemical process can be further evidenced by contrasting the sediment profiles in the algae-dominated part in the northwest lake (NW) and the macrophyte-dominated part in the southeast lake (SE) (Figure 1). That is, the sediment pH, acid-extracted Ca and Mg were all higher in NW than those in SE (Figure 6a-c), which implies that algae bloom-induced alkaline environment was more in favor of carbonate precipitation. Different than other parameters, carbonate Ca/Mg ratio presented a general decline trend on the sediment profile from the depth of 20 cm (representing around 1960s) to the surface (Figure d), and presented a higher value in SE than in NW. This different pattern is also associated with the surrounding pH. In the lower sediment pH in SE, more carbonate Mg was released to water than carbonate Ca (Figure 5), resulting in a higher Ca/Mg. However, the overall decline trend below 15cm for pH, acid-extracted Ca and Mg is yet to be explored. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 6 \u0026nbsp;Variations on sediment profiles of acid-extract Ca (a) , Mg(b), pH (c) and C/Mg in different lake part (NW: northwest lake, SE: southeast lake)\u003c/p\u003e\n\u003cp\u003e3.3\u0026nbsp;Contrast of watershed soils and lake sediments\u003c/p\u003e\n\u003cp\u003eAlthough acid-extracted Ca and Mg presented a significant correlation in both soils and sediments (p\u0026lt;0.001, Figure 7), their coefficients and variations were quite different. The coefficient between acid-extracted Ca and Mg for the sediment (r=0.944) was more significantly higher than that for the watershed soils (r=0.548). The acid-extracted Ca and Mg in watershed soils are largely parent matrix depended and vary greatly across land uses; while the watershed derived carbonate Ca and Mg has undergone the similar transportation and transformation from land to the lake. Therefore, carbonate Ca and Mg revealed a high homogeneity in the lake sediment. However, in the scatter correlation plots, there were some \u0026ldquo;outliers\u0026rdquo; (in the rectangle, Figure 7) for either sediments or soils, characterized by much higher Ca/Mg ratio. By examining these data sites, we found that the soil sites of outliers were in carbonate areas (Figure S1), and sediment sites of outliers were near the west shore or carbonate islands, which indicates the distinctive source characteristic and implies a typical linkage of these base cations between the land and water. \u0026nbsp;\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFigure 7 \u0026nbsp;Contrast of correlation between acid-extracted Ca and Mg in sediments (a) and soils (b) (Data sites in the rectangle are in or near carbonate rock areas)\u003c/p\u003e\n\u003cp\u003eFurther exploring the linkage by contrasting pH, acid-extracted Ca and Mg, and Ca/Mg ratio between the soil and sediment, we found that the lake sediment was a sink for Ca and Mg, weathered in the watershed and transported to the lake. The sediment pH was even higher than carbonate region soils (soil-C) and significantly higher than that in the non- carbonate region soils (soil-NC) (p\u0026lt;0.01, Figure 8a), because of the intensive in-lake alkalinization, particularly in the NW lake (Tao, et.al., 2016). Carbonate Ca in the sediment was only lower than that in the carbonate region soils (soil-C), but significantly higher than that in non- carbonate region soils (soil-NC) (p\u0026lt;0.01, Figure 8b), with a larger area in the watershed. In addition, carbonate Ca and Mg in the NW sediment were significantly higher than those in the SE sediment (p\u0026lt;0.01, Figure 8b and c), because the most inflow rivers transport weathered products to the lake from the northwest watershed (Figure 1). In addition, eutrophication in the NW lake is more intensive than the SE lake, which is in favor of precipitation of Ca and Mg. The lower carbonate Ca/Mg ratio in the sediment than in the soil was likely a reflection of higher solubility of carbonate Mg in waters, and some biogeochemical processes such as organism absorption or uptake of Mg during the lacustrine transportation. However, this re-distribution of base cations from the watershed to lake needs closer studies due to its potential effects on the ecosystem functioning (B\u0026eacute;rang\u0026egrave;re et al., 2016). \u0026nbsp;\u0026nbsp;\u003c/p\u003e"},{"header":"Conclusions","content":"\u003cp\u003eThe anthropogenic acidification has greatly accelerated carbonate dissolution and losses in Taihu watershed during the past five decades. Both acid deposition and N fertilization in this region contributed to the acidification and base cation (mainly Ca and Mg) losses. Soils of different land uses are impacted by acidifying effects in this watershed, and the soil of wheat-rice land is most impacted by acidification because of both intensive fertilizer application and acid deposition, while the wetland soil is only impacted by acid rains. Correspondingly, the acid-extract Ca and Mg in wheat-rice soils were significantly lower than those in wetland soils, particularly for the surface soils (0-15cm), which are more susceptible to fertilization and acid rains. Meanwhile, pH of acidification-impacted soils was universally significantly lower than that of less acidification-impacted soils. Even in the same carbonate areas in this watershed, soil pH of N-fertilized vegetable land was lower than that of wetland. Compared with 40 years ago, the average soil pH of the paddy lands in the region overall declined by at least 0.5 pH units. The accelerated carbonates weathering and base cation losses in the past decades were recorded by the lacustrine sedimentary records in Taihu lake. The sediment profile revealed an increasing trend of carbonate C and Mg concentration from the depth of 15cm (around the early 1980s) to surface, and generally higher carbonates in NW (inflow area) sediment than in SE (drainage area), indicating that the lake sediment is a major sink of the base cations transported from the watershed. However, carbonate Ca/Mg ratio had a higher value in less acidified (higher pH) environment in the watershed, but it had a higher value in lower pH environment in the lake sediment, which indicates the different effects of lacustrine ecosystem on the base cation transformation than in the terrestrial ecosystem.\u003c/p\u003e\n\u003cp\u003eAlthough the soil carbonate system currently plays the major buffering role against the acidification in the watershed due to high carbonates concentration in soils, long-term carbonate dissolution, losses of Ca and Mg, and declined soil pH would pose environmental problems and require more considerations. Furthermore, the potential effects of base cations depletion in the watershed and accumulation in the lake on species diversity and ecosystem functioning remain unclear and need evaluation. In addition, the bio-geochemical processes have changed Ca/Mg ratio between the terrestrial and lacustrine system during their transportation and transformation, and how this re-distribution alters terrestrial and aquatic ecosystem also needs higher resolution researches at both temporal and spatial level. This work helps build more generalized understandings of watershed buffering system against acidification and consequent aquatic effects, and our findings also provide basis to be incorporated into geochemical modelling so as to more accurately predict the linked environmental effect between lands and waters.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003eAcknowledgement\u003c/p\u003e\n\u003cp\u003eThis work was financially supported by the National Natural Science Foundation of China (No. 41871079), and the Open Foundation of State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences (No.SKLECRA2019OFP09 and SKLECRA2021OFP01).\u003c/p\u003e\n\u003cp\u003eEthical Approval\u003c/p\u003e\n\u003cp\u003eNot applicable \u003c/p\u003e\n\u003cp\u003eConsent to Participate\u003c/p\u003e\n\u003cp\u003eAll authors consent to participate in this research.\u003c/p\u003e\n\u003cp\u003eConsent to Publish\u003c/p\u003e\n\u003cp\u003eAll authors consent to publish this research in ESPR if accepted.\u003c/p\u003e\n\u003cp\u003eAuthors Contributions\u003c/p\u003e\n\u003cp\u003eYu Tao: Design of the research, field sampling, data analysis, writing original draft\u003c/p\u003e\n\u003cp\u003eJia Binyang: Field work coordination, data collection and support\u003c/p\u003e\n\u003cp\u003eWang Rui: Field sampling, sample treatment and measurement\u003c/p\u003e\n\u003cp\u003eDeng Yixiang: Data analysis, manuscript editing\u003c/p\u003e\n\u003cp\u003eZhuo Xiaoke: Field sampling, sample treatment and measurement，reference editing\u003c/p\u003e\n\u003cp\u003eCheng Zhonghua: Field sampling, sample treatment and measurement\u003c/p\u003e\n\u003cp\u003eHe Chengda: Sample test support, resource support\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eNational Natural Science Foundation of China (No. 41871079)\u003c/p\u003e\n\u003cp\u003eCompeting Interests\u003c/p\u003e\n\u003cp\u003eThe authors have no competing interests\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials\u003c/p\u003e\n\u003cp\u003eAll data used in this research are available for check from the corresponding author on request of the Editor.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eB\u0026eacute;rang\u0026egrave;re A, Leys GE, Likens CE, Johnson JM, Craine B, Lacroix KK, McLauchlan (2016) Natural and anthropogenic drivers of calcium depletion in a northern forest during the last millennium. PNAS 113(25):6934\u0026ndash;6938\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChen D, Lan Z, Bai X, Grace JB, Bai Y (2013) Evidence that acidification-induced declines in plant diversity and productivity are mediated by changes in below-ground communities and soil properties in a semi-arid steppe. J Ecol 101(5):1322\u0026ndash;1334\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eCheng L, Yao S, Xue B, Ling L, Liu J (2019) Long-term change of the assemblages and abundance of \u003cem\u003eCladocerans\u003c/em\u003e in different ecotypes of lake Taihu. J Lake Sci 31(6):1670\u0026ndash;1684\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eChetelat B, Liu C, Zhao Z, Wang Q, Li S, Li J, Wang B (2008) Geochemistry of the dissolved load of the Changjiang basin rivers: anthropogenic impacts and chemical weathering. Geochim Cosmochim Acta 72(17):4254\u0026ndash;4277\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo L (2007) Doing battle with the green monster of Taihu Lake. Science 317(5842):1166\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo J, Liu X, Zhang Y, Shen J, Han W, Zhang W, Christie P, Goulding KWT, Vitousek PM, Zhang F (2010) Significant acidification in major Chinese croplands. Science 327(5968):1008\u0026ndash;1010\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHongtao D, Ronghua M, Xiaofeng X, Fanxiang K, Shouxuan Z, Weijuan K, Jingyan H, Linlin S (2012) Two-decade reconstruction of algal blooms in china's lake Taihu. Environ Sci Technol 43(10):3522\u0026ndash;3528\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eJiangsu soil survey office (1995)Jiangsu Soils, China Agriculture Press, Beijing. pp335\u0026ndash;338\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaushal SS, Likens GE, Pace ML, Utz RM, Haq S, Gorman J, Grese M (2018) Freshwater salinization syndrome on a continental scale. PNAS 115(4):574\u0026ndash;583\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi Z, Yunpeng Q, Lei C, Yi W, Lingli L, Cong T, Dan CB, Kent OB, Xinmin B, Weijian Z, Shuijin H (2018) Atmospheric CO2 enrichment and reactive nitrogen inputs interactively stimulate soil cation losses and acidification. Environ Sci Technol 52(12):6895\u0026ndash;6902\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLiang T, Fang L, Cheng L, Xiong F, Li G, Bo W, Shi W, Ming X (2019) Mitigation of soil acidification through changes in soil mineralogy due to long-term fertilization in southern China. CATENA 174:227\u0026ndash;234\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLu X, Vitousek PM, Mao Q, Gilliam FS, Luo Y, Turner BL, Zhou G, Mo J (2021) Nitrogen deposition accelerates soil carbon sequestration in tropical forests.PANS.118(16), e2020790118\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMitchell MJ, Likens GE (2011) Watershed sulfur biogeochemistry: shift from atmospheric deposition dominance to climatic regulation. Environ Sci Technol 45(12):5267\u0026ndash;5271\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePan Y, Hua M, Liao Q, Xu S, Zhang Y, Zhai H (2018) Distribution properties and time-series comparisons of soil pH-values in Yixing area. Geophysi Geoche Explor 42(4):825\u0026ndash;832 (in Chinese with English abstract)\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQichao Z, Wim V, Xuejun L, Tianxiang H, Mufan Z, Jianbo S, Fusuo Z (2018) Enhanced acidification in Chinese croplands as derived from element budgets in the period 1980\u0026ndash;2010. Sci Total Environ 618(5):1497\u0026ndash;1505\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiquan L, Aiwen L, Xuelian Y, Tianfei D, Yueyue P, Dagang Y, Bin Z, Qi T, Changquan W, Bing L, Xuesong G, Yiding L, Deyong Wu, Qiang X (2020) Soil acidification of the soil profile across Chengdu Plain of China from the 1980s to 2010s. Sci. Total Environ. 698(1), 134320.1-134320.9\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRhodes AL, Newton RM, Pufall A (2001) Influences of Land Use on Water Quality of a Diverse New England Watershed. Environ Sci Technol 35(18):3640\u0026ndash;3645\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eShi K, Zhang Y, Xu H, Zhu G, Qin B, Huang C, Liu X, Zhou Y, Lv H (2015) Long-term satellite observations of microcystin concentrations in lake Taihu during cyanobacterial bloom periods. Environ Sci Technol 10(11):6448\u0026ndash;6456\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSlessarev EW, Lin Y, Bingham NL, Johnson JE, Dai Y, Schimel JP, Chadwick OA (2016) Water balance creates a threshold in soil pH at the global scale. Nature 540:567\u0026ndash;569\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSongchao C, Zongzheng L, Richard W, Ganlin Z, Yin Z, Hongfen T, Bifeng H, Dominique A, Zhou S (2019) A high-resolution map of soil pH in China made by hybrid modelling of sparse soil data and environmental covariates and its implications for pollution. Sci Total Environ 655:273\u0026ndash;283\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSulpis O, Boudreau BP, Mucci A, Jenkins C, Key RM (2018) Current CaCO\u003csub\u003e3\u003c/sub\u003e dissolution at the seafloor caused by anthropogenic CO\u003csub\u003e2\u003c/sub\u003e. PANS 115(46):11700\u0026ndash;11705\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSulpis O, Jeansson E, Dinauer A, Lauvset SK, Middelburg JJ (2021) Calcium carbonate dissolution patterns in the ocean. Nat Geosci 14(7):423\u0026ndash;428\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTao Y, Qiujin X, Chengda H, Haibing C, Dan D, Fengchang W, Wei M (2016) Long Term Trends in Acid Neutralizing Capacity under Increasing Acidic Deposition: A Special Example of Eutrophic Taihu Lake, China. Environ Sci Technol 50(23):12660\u0026ndash;12668\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTessier AP, Campbell PGC, Bisson MX (1979) Sequential extraction procedure for the speciation of particulate trace metals. Anal Chem 51(7):844\u0026ndash;851\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eTian D, Niu S (2015) A global analysis of soil acidification caused by nitrogen addition. Environ Res Lett 10(2):1714\u0026ndash;1721\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang Q, Yu H, Liu J, Li F (2018) Attribution of soil acidification in a large scale region: artificial intelligence approach application. Soil Sci Soc Am J 82:772\u0026ndash;782\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWeyhenmeyer GA, Hartmann J, Hessen DO, Kop\u0026aacute;ek J, Zechmeister T (2019) Widespread diminishing anthropogenic effects on calcium in freshwaters. Sci Rep 9(1):1\u0026ndash;10\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYang Y, Ji C, Ma W, Wang S, Wang S, Huan W, Mohamma A, Robinson D, Smith P (2012) Significant soil acidification across northern China's grasslands during 1980s-2000s. Glob Change Biol 18:2292\u0026ndash;2300\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYu T, Dai D, Lei K, He C, Cong H, Fu G, Xiu Q, Sun F, Wu F (2018) δ15N and Nutrient Stoichiometry of Water, Aquatic Organisms and Environmental Implications in Taihu lake. China Environ Pollut 237(6):166\u0026ndash;173\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYu T, Zhang Y, Wu F, Meng W (2013) Six-Decade Change in Water Chemistry of Large Freshwater Lake Taihu, China. Environ Sci Technol 47(16):9093\u0026ndash;9101\u003c/span\u003e\u003c/li\u003e\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":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Carbonates, Acidification, Soil and sediment, Ecosystem, Taihu Watershed","lastPublishedDoi":"10.21203/rs.3.rs-1556696/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-1556696/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAnthropogenic disturbances have greatly changed the water chemistry in Taihu lake, however, how soil carbonates responded to the long-term human-induced acidification received less attention likely due to the \u0026ldquo;acid-insensitive\u0026rdquo; region of Taihu watershed. In this work, we investigated soil carbonate concentrations from different land uses in the upstream of the lake and sediment carbonate profiles in the lake, to explore the linkage of carbonates dissolution in the land and sedimentation in the lake. The result showed that the wheat-rice surface soil, the most acidification-impacted by fertilization and acid deposition, had significantly lower pH than vegetable and wetland soils (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). Meanwhile, the carbonate concentration in wetland soils, only impacted by acid deposition, was significantly higher than that in wheat-rice and vegetable soils (p\u0026thinsp;\u0026lt;\u0026thinsp;0.05). The pH profile of fertilized soils, with an increasing trend from the surface to bottom, further indicated the acidifying effect of fertilization. Although the average soil pH across all land uses was 6.6 in the upstream of the lake, remaining carbonate buffering system, the significant carbonate decrease especially in surface soils evidenced the definite carbonate dissolution by acidification, which is cumulative and irreversible. Contrary to the topsoils, the sediment carbonate concentration presented an increasing trend from the depth of 15cm (denoting around the early 1980s) to surface, indicating that lake sediments are major sink of carbonate Ca and Mg from the watershed, particular under an alkaline lake environment caused by frequent algae blooms in the past decades. In addition, Ca/Mg ratio in the sediment, having higher values in a higher pH environment, was quite different from the watershed pattern, suggesting different biogeochemical processes they underwent during their transportation and sedimentation. The effects of acidification-altered re-distribution of carbonate Ca and Mg and Ca/Mg ratio in the terrestrial and aquatic environments deserve wider considerations of ecosystem consequence.\u003c/p\u003e","manuscriptTitle":"Accelerated Carbonates Dissolution Caused by Anthropogenic Acidification - Contrast of Watershed Soils to Lake Sediments in Taihu Region, China","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2022-05-17 19:20:00","doi":"10.21203/rs.3.rs-1556696/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Minor Revision","date":"2022-06-07T23:20:03+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2022-05-21T07:57:51+00:00","index":0,"fulltext":""},{"type":"editorInvitedReview","content":"","date":"2022-05-15T13:49:45+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2022-05-15T06:11:15+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2022-05-10T16:52:30+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2022-04-25T05:31:08+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2022-04-14T02:24:05+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"b1ad74ef-42d1-479f-a71a-5044fb4094cd","owner":[],"postedDate":"May 17th, 2022","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2022-06-26T02:20:01+00:00","versionOfRecord":[],"versionCreatedAt":"2022-05-17 19:20:00","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-1556696","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-1556696","identity":"rs-1556696","version":["v1"]},"buildId":"369fNeqWncA4NS6XSWjrt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}