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Metal stable isotopes in marine carbonates have been widely used as novel proxies for metal cycling through the geological past. Amongst these metals, copper (Cu) and zinc (Zn) have received great attention owing to their vital roles in metabolic processes. However, whether modern marine biogenic carbonates record the seawater isotope signatures of Cu (δ65Cu) and Zn (δ66Zn) and mechanisms and factors controlling isotope fractionation of these metals remain unclear, hindering applications of both isotope systems in paleoceanography. Here we present annually-resolved records of δ65Cu and δ66Zn in seven coral (Porites) cores sampled from different marine settings in the South China Sea and the Luzon Strait, western Pacific. We find that the aragonitic skeletons of corals are enriched in light Cu but heavy Zn isotopes relative to surface seawaters, with δ65Cu and δ66Zn in the range of −0.16 ± 0.06‰ to 0.40 ± 0.05‰ and 0.06 ± 0.04‰ to 0.46 ± 0.08‰ (2SD), respectively. The coral δ65Cu exhibits significant inter- and intra-colony variations, which are most likely controlled by Rayleigh-type fractionation in the calcifying fluids of corals rather than by changes in environmental factors or seawater δ65Cu. We thus suggest that δ65Cu in ancient carbonates may not be a direct record of Cu isotope compositions in coeval seawaters. In contrast, coral δ66Zn shows insignificant temporal variation, and the Zn isotope fractionation between individual corals and seawaters are relatively small and constant (0.10 ± 0.05‰, n = 33, 2SD). This limited Zn isotope fractionation is much lower than that determined during inorganic precipitation of calcite, which is likely due to pH up-regulation by the coral that changes aqueous Zn speciation, and preferential organic complexation of the heavy Zn isotopes in the calcifying fluids. Therefore, Porites corals are promising archives for tracking historical changes of surface seawater δ66Zn. Our new datasets of reef carbonates, particularly the coral δ65Cu values which are measured for the first time, could provide a better constrain on marine Cu and Zn geochemistry and their modern oceanic mass and isotope budgets.

Mantle degassing transect across different tectonic units within a plate convergent setting has been well documented for oceanic convergent margins by systematic changes in geochemistry (e.g., 3He/4He, δ13C, and CO2/3He) of hydrothermal gases. However, little is known about spatial variations in volatile geochemistry across a continental convergent margin. In this study, we identify a mantle degassing transect in the southeastern Tibetan Plateau using He-CO2 systematics of hydrothermal gases, which extends from India-Asia continental convergent margin to intra-continent extensional region. δ13C-CO2 (−11.8‰ to −3.1‰) and CO2/3He (1.7 × 108 to 7.1 × 1011) values of hydrothermal gases show large variations that are consistent with modification by secondary physico-chemical processes, such as multi-component mixing, hydrothermal degassing, and calcite precipitation. Three levels of He degassing can be recognized based on 3He/4He dataset (0.01–5.87 RA) of the hydrothermal gas samples and their distances to volcanic centers. A magmatic level He degassing (35–74% mantle He) is found near active and/or Quaternary volcanoes fed by mantle-derived magmas. With increasing distance to volcanic centers, the outgassed magmatic volatiles are gradually diluted by crustal components (e.g., radiogenic 4He), defining a transitional level He degassing (13–33% mantle He). The 3He/4He values (8.16–8.48 RA) of olivine phenocrysts indicate a MORB (mid-ocean ridge basalts)-type mantle source for the magmatic and transitional levels of He degassing that are localized in Quaternary volcanic fields. In contrast, a background level He degassing (

A large number of gases are releasing from the medium-high temperature geothermal fields distributed along the large-scale strike-slip fault zones in the southeastern margin of the Tibetan Plateau. In this study, 11 hot spring water and the associated bubbling gas samples were collected along the Xianshuihe-Anninghe fault zones (XSH-ANHFZ) and analyzed for chemical and isotopic compositions. The $${\delta ^{18}}{{\rm{O}}_{{{\rm{H}}_2}{\rm{O}}}}$$ and $$\delta {{\rm{D}}_{{{\rm{H}}_2}{\rm{O}}}}$$ values indicate that hot spring waters are predominantly meteoric origin recharged from different altitudes. Most water samples are significantly enriched in Na+ and HCO3− due to the dissolution of regional evaporites, carbonates and Na-silicates. 3He/4He ratios of the gas samples are 0.025–2.73 times the atmospheric value. The 3He/4He ratios are high in the Kangding region where the dense faults are distributed, and gradually decrease with increasing distance from Kangding towards both sides along the Xianshuihe fault zones (XSHFZ). Hydrothermal fluids have dissolved inorganic carbon (DIC) concentrations from 2 to 42 mmol L−1, δ13CDIC from −6.9‰ to 1.3‰, $${\delta ^{13}}{{\rm{C}}_{{\rm{C}}{{\rm{O}}_2}}}$$ from −7.2‰ to −3.6‰ and Δ14C from −997‰ to −909‰. Combining regional geochemical and geological information, the CO2 sources can be attributed to deep-sourced CO2 from mantle and metamorphism of marine carbonate, and shallow-sourced CO2 from the dissolution of marine carbonate and biogenic CO2. The mass balance model shows that 11±6% of the DIC is sourced from the dissolution of shallow carbonate minerals, 9±8% formed by pyrolysis of sedimentary organic matter, 80±9% derived from deep metamorphic origin and mantle-derived CO2. Among them, the deep-sourced CO2 in Anninghe fault zones (ANHFZ) is merely metamorphic carbon, whereas ca. 12% and ca. 88% of the deep-sourced CO2 in the XSHFZ are derived from the mantle and metamorphic carbon, respectively. The average deep-sourced CO2 flux in the Kangding geothermal field is estimated to be 160 t a−1. If all the hot springs in various fault zones in the southeastern margin of the Tibetan Plateau are taken into account, the regional deep-sourced CO2 flux would reach ca. 105 t a−1. These results show that the deep-sourced CO2 released from non-volcanic areas might account for a considerable proportion of the total amount of global deep-sourced carbon degassing, which should be paid more attention to.

The episodic growth of high-elevation orogenic plateaux is controlled by a series of geodynamic processes. However, determining the underlying mechanisms that drive plateau growth dynamics over geological history and constraining the depths at which growth originates, remains challenging. Here we present He-CO2-N2 systematics of hydrothermal fluids that reveal the existence of a lithospheric-scale fault system in the southeastern Tibetan Plateau, whereby multi-stage plateau growth occurred in the geological past and continues to the present. He isotopes provide unambiguous evidence for the involvement of mantle-scale dynamics in lateral expansion and localized surface uplift of the Tibetan Plateau. The excellent correlation between 3He/4He values and strain rates, along the strike of Indian indentation into Asia, suggests non-uniform distribution of stresses between the plateau boundary and interior, which modulate southeastward growth of the Tibetan Plateau within the context of India-Asia convergence. Our results demonstrate that deeply-sourced volatile geochemistry can be used to constrain deep dynamic processes involved in orogenic plateau growth., Deeply-sourced volatiles are releasing from orogenic plateau regions, providing windows to plateau growth dynamics occurring at variable depths. Here the authors show that mantle-derived volatiles reveal the involvement of mantle dynamics in southeastward growth of the Tibetan Plateau.

Landscape evolution is modulated by the regional tectonic uplift, climate change, and river dynamics. However, how to distinguish these mechanisms through the research of surface exhumation and fluvial incision remains controversial. In this study, cosmogenic 10Be, 26Al, and 21Ne concentrations in quartz from cave deposits, modern river sediments, and bedrocks were measured to constrain the applicability of cosmogenic 21Ne and discuss Quaternary landscape evolution history in the Guizhou Plateau, southeast China. Using the 26Al-10Be and 21Ne-10Be pairs to distinguish the cosmogenic 21Ne concentration from the excess 21Ne, we found that the nucleogenic 21Ne produced by the U and Th decay in quartz is significant in the samples although there is the possibility of inherited cosmogenic 21Ne. Combining with previous studies, we suggest that the precise approach for applying the cosmogenic 21Ne could be reached by (1) estimating the contribution from nucleogenic 21Ne, (2) avoiding samples with complex burial histories to exclude inherited cosmogenic 21Ne, and (3) combining the 10Be-26Al-21Ne nuclides method for the Quaternary samples. In addition, both pre-burial basin denudation rates and burial ages derived from the 26Al-10Be pair were used to determine the different timescale surface denudation rate and fluvial incision rate in relation to previous work. The consistency of the different timescales pre-burial basin denudation rate, 36Cl surface denudation rate, and modern basin denudation rate indicates that the landscape-scale surface denudation has been likely stabilized since the Quaternary in the Guizhou Plateau area. The slightly higher river incision rates than the local surface denudation rate show that the river dynamics may not have reached a steady-state due to the regional tectonic uplift in the Guizhou Plateau.

Tectonically active high relief areas are proposed to have a substantial impact on climate regulation throughout the Cenozoic. Here, we present lithium (Li) isotope data of the dissolved load and suspended particulate material from the basins of the Yalong River and the Jinsha River, which drain the high-relief borders of the eastern Tibetan Plateau and constitute the headwaters of the Yangtze River. Dissolved δ7Li values are relatively low and constant in the Jinsha River mainstream (+6.8‰ to +9.7‰) compared to the higher and downstream increasing values in the Yalong River mainstream (+10.8‰ to +17.5‰). Furthermore, dissolved δ7Li values in the major tributaries of the Jinsha and Yalong River are highly variable and increase downstream from +11.4‰ to +29.4‰ and from +9.0‰ to +23.6‰, respectively. Robust correlations between Li, Na, and Cl concentrations identify that evaporite dissolution in the uppermost headwaters of the Jinsha River basin controls the Li budget and riverine δ7Li values of the mainstream and has a significant impact on dissolved Li in the Yangtze River. In contrast to the Jinsha River mainstream, dissolved Li in the Yalong River mainstream and the Jinsha and Yalong River tributaries are dominantly derived from the dissolution of silicates. δ7Li variations in the Yalong River basin and the Jinsha tributaries reflect little Li uptake by clays in the upper reaches and more Li uptake by clays in the lower reaches of the river basins. SWR/D ratios (where SWR is the chemical silicate weathering rate, and D is the total denudation rate) highlight an intermediate silicate weathering intensity under a kinetically limited weathering regime for the study area. However, positive correlations between dissolved δ7Li value and silicate weathering intensity proxies (such as Si/(Nasil + K) and K/(Nasil + K)) indicate an increasing weathering intensity downstream. A positive correlation between dissolved δ7Li values and the annual precipitation and a negative one between δ7Li values and elevation indicates that larger annual precipitation under a flattening relief results in a stronger silicate weathering intensity, thus, more Li uptake in clays and higher riverine δ7Li values in the lower reaches. Compared to the lower reaches of Yangtze River basin (∼+20‰), lower dissolved δ7Li values in its headwater of this study suggest that the increase in δ7Li of seawater over the Cenozoic is influenced by weathering in floodplains that developed due to erosion of high mountains, rather than weathering of mountain belts itself. Combined with silicate weathering rates of the eastern border of the Tibetan Plateau, the highest riverine δ7Li values in its catchments come along with the highest silicate weathering rates and high CO2 consumption, suggesting that a more elevated topography may have an important role in the drawdown of CO2 during the Cenozoic.

Planktonic bacteria and archaea play a key role in maintaining ecological functions in aquatic ecosystems; however, their biogeographic patterns and underlying mechanisms have not been well known in coastal wetlands including multiple types and at a large space scale. Therefore, planktonic bacteria and archaea and related environmental factors were investigated in twenty-one wetlands along China’s coast to understand the above concerns. The results indicated that planktonic bacteria had different biogeographic pattern from planktonic archaea, and both patterns were not dependent on the wetland's types. Deterministic selection shapes the former’s community structure, whereas stochastic processes regulate the latter’s, being consistent with the fact that planktonic archaea have a larger niche breadth than planktonic bacteria. Planktonic bacteria and archaea co-occur, and their co-occurrence rather than salinity is more important in shaping their community structure although salinity is found to be a main environmental deterministic factor in the coastal wetland waters. This study highlights the role of planktonic bacteria-archaea co-occurrence on their biogeographic patterns, and thus provides a new insight into studying underlying mechanisms of microbial biogeography in coastal wetlands. Supplementary Information The online version contains supplementary material available at 10.1186/s40793-021-00388-9.

Based on Terrestrial Cosmogenic Nuclide (TCN) constraints from depth profiles of one granitic regolith from Wumingshan and five fluvial terraces from Xianshuihe and Zagunao rivers, we discuss the timing of the last deglaciation, the landscape-scale denudation and fluvial incision rates across the eastern Tibetan Plateau, in relation to previous work. We present a three-dimensional-graph visualization approach and corresponding constraints to better assess the feasibility and applicability of cosmogenic nuclides depth-profile dating. The exposure age (older than 19.4 ka) of the Wumingshan regolith corresponds to the retreat of the palaeo-Daocheng ice cap, which covered the Yidun terrane during the Last Glacial Maximum (LGM). Most basin-wide denudation rate data in the eastern Tibetan Plateau are lower than 130 mm/ka (47%, n = 90), which is consistent with the Wumingshan regolith denudation rate (lower than 52.8 mm/ka), and thus indicate that the landscape-scale denudation has been stabilized after the last deglaciation. Considering the reduction of integrated bulk density due to the accumulation of lower-density loess, we estimate mean exposure ages of Xianshuihe and Zagunao river terraces of 4.0 ± 0.7 ka, 5.9 ± 0.3 ka, 13.4 ± 2.0 ka, and 16.6 ± 1.4 ka. The observed increase in incision rate from 0.39 mm/yr over long timescale (∼600 ka) to 5.88 mm/yr over the last 15 ka at the Xianshuihe river site is probably due to the transition from glacial to interglacial climatic conditions. The fewer abandoned terraces along the Zagunao river after the Heinrich event 1 (H1) indicates that the climate change during the latest glacial-interglacial transition impacted less the landscape evolution in a relatively lower elevation area. Comparison with previously reported fluvial incision rates elsewhere across the eastern margin of the Tibetan Plateau indicates that incision rates are mainly influenced by abrupt climate change or intensified summer monsoon since the early Holocene, but probably controlled by regional tectonic uplift or fluvial headward retreat as the timescale increases. Overall, we propose a synthetic pattern of landscape evolution mainly dominated by long-term tectonic uplift together with fluvial headward erosion, episodically influenced by climatic change throughout the late Quaternary.

Zn isotope is a useful tool for tracing biogeochemical processes as zinc plays important roles in the biogeochemistry of natural systems. However, the Zn isotope composition in the lake ecosystems has not been well characterized. In order to resolve this problem, we investigate the Zn isotope compositions of suspended particulate matter (SPM) and biological samples collected from the Aha Lake and Hongfeng Lake, and their tributaries in summer and winter, aiming to explore the potential of this novel isotope system as a proxy for biogeochemical processes in aqueous environments. Concentration of dissolved Zn ranges from 0.65 to 5.06 μg/L and 0.74 to 12.04 μg/L for Aha Lake and Hongfeng Lake, respectively, while Zn (SPM) ranges from 0.18 to 0.70 mg/g and 0.24 to 0.75 mg/g for Aha Lake and Hongfeng Lake, respectively. The Zn isotope composition in SPM from Aha Lake and its main tributaries ranges from -0.18‰ to 0.27‰ and -0.17‰ to 0.46‰, respectively, and it varies from -0.29‰ to 0.26‰ and -0.04‰ to 0.48‰, respectively in Hongfeng Lake and its main tributaries, displaying a wider range in tributaries than lakes. These results imply that Zn isotope compositions are mainly affected by tributaries inputting into Aha Lake, while adsorption process by algae is the major factor for the Zn isotope composition in Hongfeng Lake, and ZnS precipitation leads to the light Zn isotope composition of SPM in summer. These data and results provide the basic information of the Zn isotope for the lake ecosystem, and promote the application of Zn isotope in biogeochemistry.

Soil water stable isotope compositions (SWSI; i.e., δD and δ18O) and soil moisture content (SMC) are widely used to illuminate water exchange processes across the atmosphere-land interface. Thus, the knowledge of spatiotemporal dynamics of these two variables is critical to help our understanding of relevant ecohydrological processes. However, in comparison to the efforts for elucidating the spatiotemporal variability in SMC, much less attention was paid to understand the spatiotemporal variability in SWSI, which also raises the question as to whether SWSI and SMC share similar spatiotemporal features. To this end, the spatiotemporal dynamics of SWSI and SMC were jointly investigated on a karst hillslope with eight sampling campaigns among two years. The method of temporal stability analysis (TSA) was adopted to evaluate the spatiotemporal patterns of SWSI and SMC in this study. Generally, both δD and δ18O exhibited considerable temporal and spatial variations; meanwhile, the variations in δD and δ18O values were relatively smaller than that of SMC. In addition, in comparison with the spatial pattern of SMC, there were no clear relationships between the standard deviation (SD) and the spatial mean of δD or δ18O. However, the SD of line-conditioned excess (lc-excess) and its mean values displayed a strong negative correlation, indicating that the spatial variations in lc-excess increased with soil evaporation. Moreover, SWSI displayed weaker temporal stability than SMC and no clear controlling factors were identified, suggesting that the spatiotemporal dynamics of SWSI might be more complex than that of SMC. This study provided comprehensive field evidence that there existed profound spatiotemporal variability in SWSI and its spatiotemporal features were different from SMC, highlighting that the spatiotemporal variability in SWSI needs to be considered in isotope-based estimations and it should be investigated separately from the spatiotemporal characteristics of SMC in future studies.

This study aims to clarify the relationship between chemical weathering of rocks and the carbon budget of rivers and better understand the weathering mechanisms of plateau watersheds. We chose to study the Jinsha River, which originates from the Tibetan Plateau and also is in the upper reaches of the Changjiang River. Analysis of hydrochemistry, radiogenic strontium isotope and stable calcium isotopes were conducted of the Jinsha River water samples, which were collected along its mainstream and main tributaries in the summer. The results show that the water chemistry of the mainstream waters is dominated by evaporite weathering, which have low 87Sr/86Sr values (0.7098–0.7108) and wide range of Sr contents (2.70–9.35 μmol/L). In contrast, tributaries of the Jinsha River have higher 87Sr/86Sr (0.7090–0.7157) and lower Sr contents (∼1 μmol/L). Moreover, the Ca isotopic compositions in the mainstream (0.87–1.11‰) are heavier than the tributaries (0.68–0.88‰) and could not be fully explained by the conventional mixing of different sources. We suggest that secondary carbonate precipitation fractionates Ca isotopes in the Jinsha River, and fractionation factors are between 0.99935 and 0.99963. At least 66% of Ca was removed in the mainstream of the Jinsha River through secondary mineral precipitation, and the average value is ∼35% in the tributaries. The results highlight that evaporite weathering results in more carbonate precipitation influencing Ca transportation and cycling in the riverine system constrained by stable Ca isotopic compositions and water chemistry.

The feedbacks of climate variability on CO2 consumption fluxes and carbon dynamics are thought to play an important role in moderating the global carbon cycle. High-frequency sampling campaigns and analyses were conducted in this study to investigate temporal variations of river water chemistry and the impacts of climate variability on CO2 consumption fluxes and carbon dynamics for the Xijiang River, Southwest China. Physical processes modify biogeochemical processes, so major ions display different responses to changing discharge. The annual CO2 consumption rate is (6.8 +/- 0.2) x 10(6) ton/year by carbonate weathering and (2.4 +/- 0.3) x 10(6) ton/year by silicate weathering. The annual CO2 consumption flux is much higher than most world rivers, and strong CO2 consumption capacities are observed in catchments in Southwest China. Lower negative delta C-13(DIC) values are found in the high-flow season which corresponds with high temperatures compared to those in the low-flow season. High discharge will accelerate material transport, and high temperatures will increase primary production in the catchment, both of which can be responsible for the shift of delta C-13(DIC) values in the high-flow season. Increased mineral weathering and biological carbon influx in the catchment are the main factors controlling carbon dynamics. Overall, these findings highlight the sensitivity of CO2 consumption fluxes and carbon dynamics in response to climate variability in the riverine systems. Plain Language Summary There are feedbacks between climate variability and CO2 consumption fluxes by chemical weathering and carbon dynamics. Significant temporal variations of major ions and delta C-13(DIC) are observed in the Xijiang River. Multiple biogeochemical processes occur under various hydrological conditions, shifting major ions concentrations, and delta C-13(DIC). The annual CO2 consumption rate is (6.8 +/- 0.2) x 10(6) ton/year by carbonate weathering and (2.4 +/- 0.3) x 10(6) ton/year by silicate weathering. The annual CO2 consumption rates in the Xijiang River only account for a small fraction in the global CO2 consumption rates; the CO2 consumption capacity is much higher than the global average, while much lower than its source tributaries (Beipan and Nanpan Rivers). Slow subsurface flow paths with longer transit times switch to rapid near-surface flow paths with shorter transit times, as discharge increases. High temperatures increase reaction rates, and high discharge rates remove transport limitation, both of which would accelerate the chemical weathering rates. In the high-flow season, high discharge accompanying with high temperatures, large amounts of delta C-13-depleted biological carbon, flushes into the river, affecting the carbon dynamics.

Land use and land cover (LULC) products derived from remote sensing data are fundamental to the earth's surface ecological environment studies. Various LULC products have different data sources with large uncertainties and varying spatio-temporal resolutions. In this study, our objectives are to understand the accuracy of the current LULC products at the coastal area of Tianjin city. We conducted accuracy verification and comparative analysis of the LULC datasets available from different sources, MCD12Q1, CGLS-LC100, FROM_GLC, GLC_FCS30 and GlobeLand30 for the years of 2010, 2015, 2017 and 2020, at varying spatial resolutions 500–100–30–10 m. Using land cover dataset for these years, we conducted time-series analysis of land cover changes and driving factors. Results showed that GLC_FCS30-2020 has the highest classification accuracy (72.57%), followed by GlobeLand30-2020 (72.23%) and GlobeLand30-2010 (70.10%). The classification accuracy is related to the spatial resolution of original data source and the classification system. The verification accuracies of all products are found to be lower than their official announcements. Additionally, the accuracy comparison among different land types indicated that the classification accuracy of agricultural land, impervious surface, and water bodies is high, while that of forest, grassland, and shrubs is low. According to the spatio-temporal pattern analysis of land cover changes in Tianjin during 2010–2020, the area of agricultural land is slowly decreasing, and construction land is increasing, and the increase results mainly from the conversion of agricultural land and grassland. The rapid population growth, economic development and policy guidance are the main driving factors.

Understanding of the binding characteristics of wetland dissolved organic matter (DOM) and different metals is important for the quantitative assessment of the environmental behavior of metals in wetlands. In this study, different types of spectroscopy including ultraviolet-visible absorption, Fourier transform infrared, and fluorescence spectroscopy was used to investigate the binding characteristics of Fe3+, Cu2+, Cr3+, Cd2+, and Zn2+ with DOM from wetland water. Differential absorption spectra identified binding sites for these five metals in this wetland DOM at 210 nm, 280 nm, 335 nm, and > 400 nm regions. The low binding capacity of DOM in this wetland with Cd and Zn indicated that the toxicity and environmental effects of these metals in this wetland warrant further study. The calculated △EEM combined with fluorescence regional integration (FRI) analysis clearly revealed that Fe and Cu preferred to bind with humic-like DOM while Cd and Zn preferred to bind with protein-like DOM in this wetland. △EEM successfully demonstrated the characteristics of DOM complexing with different metals and could be a compelling tool in evaluating metal-DOM interactions. In addition, 2D-FTIR-COS identified the binding sites and the dynamic processes of binding at the functional group level. Metals preferentially bind with the C O, C O functional group, and then binds to the O H functional group. This study revealed that different DOM components will facilitate the migration of different metals in the environment and provided new slights into an improved understanding of migration and transformation of metals in aquatic environments.

Extensional rift systems provide important pathways for the release of large amounts of deeply-sourced CO2 into the atmosphere. Continental rifting zones (e.g., East African rift) are thus invoked to be important for understanding the links between CO2 outgassing and global climate change associated with continental breakup. However, deeply-sourced CO2 emissions from extensional rift systems in continental collision zones remain poorly understood. Here, we focus on hydrothermal CO2 emissions from the southern segment of the Yadong-Gulu rift (YGR), the largest extensional rift in southern Tibetan Plateau, aiming at delineating rift-related CO2 emissions from the India-Asia continental collision zone. In-situ measurements of diffuse soil CO2 emissions indicate that average soil CO2 fluxes from the Kangbu, Mengzha, and Chaduo hydrothermal fields are 40, 700, and 255 g m−2 d−1, respectively. Combined with average soil CO2 fluxes (20–437 g m−2 d−1) from central and northern YGR, we speculate a relatively steady-state CO2 degassing pattern for the entire rift. The magnitude of soil CO2 fluxes of the YGR is higher than that of representative areas of the East African rift system. Evidence from 3He/4He reveals a pure crustal origin for CO2-bearing fluids in southern YGR, while the involvement of mantle CO2 is recognized in the central and northern rift segments. We suggest that metamorphic decarbonation of crustal rocks at variable depths is the primary cause for CO2 origin in southern YGR, which differs from the magma‑carbonate interaction model of central and northern YGR. Ternary mixing calculation based on He-CO2 systematics of hydrothermal gases indicates dominant contributions from carbonate rocks to total carbon inventory, with mantle CO2 contributions absent in southern YGR but discernible in northern YGR. The characteristic high proportions of crustal CO2 (>90%) distinguish the YGR from extensional rifts fed primarily by mantle CO2 in continental rifting zones. Our results reveal a crustal-scale carbon cycle in accretionary wedge of the India-Asia continental collision zone, together with magmatic front setting of the central and northern YGR, outlining a transect of the rift-related CO2 emissions across continental collision zones. This would contribute to better understanding the role of continental assembly in deeply-sourced CO2 emissions and global carbon budget.

The present study seeks to evaluate the application of the 238U-234U-230Th radioactive disequilibrium methodology for the determination of the regolith production rates in thick weathering profiles marked by long histories, encountered under various climate regimes, but still very little studied by these techniques. For this purpose, 238U-234U-230Th disequilibria have been analyzed in the top 11 m of a lateritic profile developed on a granitic bedrock in south China (Longnan, Jiangxi Province) under a subtropical climate. The results demonstrate that in such a weathering profile the determination of weathering rates from the analysis of U-series nuclides in bulk rock samples cannot be recovered by applying in one step to the entire alteration profile the modeling approach classically used to interpret the U-series nuclides, i.e. the “gain and loss” model. The modeling has to be made on subsections of relatively small size (

Rare earth elements (REEs) can record geologic and geochemical processes. We studied two granitic regolith profiles from different climatic zones in eastern Tibetan Plateau and found that (1) ΣREEs ranged from 119.65 to 275.33 mg/kg in profile ND and 5.11–474.55 mg/kg in profile GTC, with average values of 205.79 and 161 mg/kg, respectively. ΣREEs was higher in accumulation horizon and semi-regolith; (2) Influenced by climate, the fractionation of light and heavy REEs (LREEs and HREEs) varied during weathering. The ratio of LREEs/HREEs in pedosphere was higher than semi-regolith in tropical profile; (3) A negative Eu anomaly in both profiles was the result of bedrock weathering. A positive Ce anomaly was observed in all layers of profile ND, and only in the upper 100 cm of profile GTC. This indicates that redox conditions along the regolith profile varied considerably with climate. (4) Normalized by chondrite, LREEs accumulated much more than HREEs; REE distribution curves were right-leaning with a V-type Eu anomaly in both profiles.

This study focuses on the chemical and Sr isotopic compositions of the dissolved load of the rivers in the Liao River basin, which is one of the principal river systems in northeast China. Water samples were collected from both the tributaries and the main channel of the Liao River, Daling River and Hun-Tai River. Chemical and isotopic analyses indicated that four major reservoirs (carbonates (+gypsum), silicates, evaporites and anthropogenic inputs) contribute to the total dissolved solutes. Other than carbonate (+gypsum) weathering, anthropogenic inputs provide the majority of the solutes in the river water. The estimated chemical weathering rates (as TDS) of silicate, carbonate (+gypsum) and evaporites are 0.28, 3.12 and 0.75 t/km2/yr for the main stream of the Liao River and 7.01, 25.0 and 2.80 t/km2/yr for the Daliao River, respectively. The associated CO2 consumption rates by silicate weathering and carbonate (+gypsum) weathering are 10.1 and 9.94 × 103 mol/km2/yr in the main stream of the Liao River and 69.0 and 80.4 × 103 mol/km2/yr in the Hun-Tai River, respectively. The Daling River basin has the highest silicate weathering rate (TDSsil, 3.84 t/km2/yr), and the Hun-Tai River has the highest carbonate weathering rate (TDScarb, 25.0 t/km2/yr). The Raoyang River, with an anthropogenic cation input fraction of up to 49%, has the lowest chemical weathering rates, which indicates that human impact is not a negligible parameter when studying the chemical weathering of these rivers. Both short-term and long-term study of riverine dissolved loads are needed to a better understanding of the chemical weathering and controlling factors.

Carbon-climate feedback is sensitive in the Qinghai-Tibet Plateau. A series of temporal measurements from Jinsha River and Yalong River, in conjunction with flow information, were used to study the carbon dynamics and predict future carbon fluxes under ongoing climate change. DIC and DOC concentrations showed considerable temporal variations, with low DIC and high DOC concentrations in the high-flow season, and vice versa. DIC and DOC concentrations had negative and positive relationships with runoff changes, respectively, showing the hydro-biogeochemical controls on carbon dynamics. With the increase of runoff, the accelerated chemical weathering and the high carbonate buffering capacity should be responsible for the chemostatic behaviors of DIC. Meanwhile, warm weather would enhance organic carbon degradation, and also thicken the active layer of permafrost in the source area, both of which would produce DOC. In addition, organic carbon degradation in the high-flow season would produce DIC with 13C-depleted values. δ13CDIC also had significant temporal variations, synchronous with runoff changes (i.e., light values under high runoff conditions), supporting that biological carbon plays an important role in carbon dynamics during the warm season. Based on the clear positive correlations between carbon fluxes and runoff, we predicted that the sensitivities of DOC fluxes to temperature changes are 12.2%/°C and 8.3%/°C for the Jinsha River and Yalong River, respectively. The sensitivities of DIC fluxes to temperature changes are much lower, which are 5.5%/°C and 6.1%/°C for the Jinsha River and Yalong River, respectively. This study sheds lights on the alpine riverine carbon cycling based on runoff-shifting concentration-isotope (q-C-I) relationships in the Qinghai-Tibet Plateau, which has implications on the understanding of climate forcing on carbon fluxes in alpine areas.

Carbon dioxide (CO2) emissions from aquatic surface to the atmosphere has been recognized as a significant factor contributing to the global carbon budget and environmental change. The influence of river damming on the CO2emissions from reservoirs remains poorly constrained. This is hypothetically due to the change of hydraulic retention time (HRT) and thermal stratification intensity of reservoirs (related to the normal water level, NWL). To test this hypothesis, we quantified CO2fluxes and related parameters in eight karst reservoirs on the Wujiang River, Southwest China. Our results showed that there was a significant difference in the values ofpCO2(mean = 3205.7μatm, SD = 2183.4μatm) andδ13CCO2(mean = −18.9‰, SD = 1.6‰) in the cascade reservoirs, suggesting that multiple processes regulate CO2production. Moreover, the calculated CO2fluxes showed obvious spatiotemporal variations, ranging from −9.0 to 2269.3 mmol m−2d−1, with an average of 260.1 mmol m−2d−1. Interestingly, the CO2flux andδ13CCO2from reservoirs of this study and other reservoirs around the world had an exponential function with the reservoir effect index (Ri, HRT/NWL), suggesting the viability of our hypothesis on reservoir CO2emission. This empirical function will help to estimate CO2emissions from global reservoirs and provide theoretical support for reservoir regulation to mitigate carbon emission.

High levels of dissolved arsenic (As) have been reported in many rivers running though the Tibetan Plateau (TP), the “Water Tower of Asia”. However, the source, spatiotemporal variations, and geochemical behavior of dissolved As in these rivers remain poorly understood. In this study, hot spring, river water, and suspended particulate material samples collected from the Yarlung Tsangpo River (YTR) (upper reaches of the Brahmaputra River) system in 2017 and 2018 were analyzed. Spatial results shown that the upper reaches of YTR (Zone I) have comparatively high levels of dissolved As ([As]dissolved: mean 31.7 μg/L; 4.7–81.6 μg/L; n = 16), while the tributaries of the lower reaches (Zone II) have relatively low levels (mean 0.54 μg/L; 0.11–1.3 μg/L; n = 7). Seasonal results shown that the high [As]dissolved (6.1–22.4 μg/L) were found in September to June and low [As]dissolved (1.4–3.7 μg/L) were observed in July to August. Geothermal water is suspected as the main source of the elevated As levels in YTR due to the extremely high [As]dissolved in hot springs (1.13–9.76 mg/L) and abundance of geothermal systems throughout TP. However, the seasonal results suggested that weathering of As-containing rocks and minerals is also a key factor affecting the [As]dissolved in the river water in July to August (wet-season). Natural attenuation of As in main channel is dominated by dilution process due to the lower As concentrations in tributaries, but mostly occurred by both dilution and adsorption (or co-precipitation) processes in tributaries. This work highlights that the weathering process may have an important contribution to the dissolved As in the river waters in wet-season, and the geochemical behavior of As is largely transported conservatively in the main channel and relative non-conservatively in the tributaries in YTR system.

The studies in this Special Issue addressed environmental and ecological issues at the karst areas in the Southwest China. The contributions from these studies indicated that some active agricultural practices that were carried out in recent years reduced environmental risk and increased economic benefits at the karst areas. The results of ecosystem service value estimates in recent years showed improvements of ecosystem and environment in karst areas of China. Local farmers and government have realized the importance of protection of environment and ecosystem than before, which might promote to seek sustainable development goal in future. These studies have delivered new knowledgement that addressed the challenges of facilitating environmental sustainability with agricultural development in the karst region of South China. Meanwhile, further research should deepen science advances to improve the resilience of soil and water resources to agricultural practices in the fragile karst ecosystem.

Hydrological conditions are a critical factor for phytoplankton ecology in hydroelectric reservoirs, and how this factor contributes to the succession of phytoplankton functional groups is still unclear. Therefore, we investigated the phytoplankton functional groups, relative water column stability, and related environmental factors in the Wujiang cascade reservoirs to understand this process. Altogether five phyla and thirteen functional groups were identified, and they showed evident variations across space and time. The B, D, P, and J groups were dominant, and the Lo and X1 groups existed only in the reservoirs. Relative water column stability rather than nutrient availability affects the succession and distribution of phytoplankton functional groups in the study area, and high relative water column stability usually increases phytoplankton biomass. This indicates that hydrologic conditions are an important factor controlling phytoplankton composition in hydroelectric reservoirs, and this study enriches the understanding of reservoir phytoplankton ecology.

Study region The impounded Wujiang River, Southwest China. Study focus Thermal stratification is an important factor shaping aquatic ecosystems in karst hydropower reservoirs. However, the underlying mechanism of thermal stratification formation is still unclear. Therefore, water temperature and related environmental factors were investigated to understand how reservoir hydraulic load (i.e., the ratio of the mean water depth to water retention time) affects thermal stratification in eight karst hydropower reservoirs on the Wujiang River. New hydrological insights for the region The reservoir surface water had a higher temperature than the inflowing and released waters. The variation in the reservoir thermal stratification showed an obvious seasonal pattern, but the extents of the thermal stratification were different among the reservoirs. The rate of water temperature change is proposed to characterize reservoir thermal stratification and is significantly negatively correlated with reservoir hydraulic load, suggesting the control of both water depth and retention time on thermal stratification. This empirical relationship will be helpful in quantitatively evaluating the hydrological effect on thermal stratification, which further affects basic environmental parameters (including pH, dissolved oxygen, and chlorophyll a) in narrow and deep karst cascade hydropower reservoirs.

Understanding where nitrate is mobilized from and under what conditions is required to reduce nitrate loss and protect water quality. Low frequency sampling may inadequately capture hydrological and biogeochemical processes that will influence nitrate behavior. We used high-frequency isotope sampling and in-situ nitrate sensing to explore nitrate export and transformation in a karst critical zone. Nitrate was mobilised during light rainfall, and transferred from soil layers to the karst matrix, where some nitrate was retained and denitrified. Nitrate isotopic composition changed rapidly during the rising limb of events and slowly during the falling limb. The main nitrate source was synthetic fertiliser (up to 80% during event flow), transported by conduit flow following high rainfall events, and this contribution increased significantly as discharge increased. Soil organic nitrogen contribution remained constant indicating at baseflow this is the primary source. Isotope source appointment of nitrate export revealed that synthetic fertilizer accounted for more than half of the total nitrate export, which is double that of the secondary source (soil organic nitrogen), providing valuable information to inform catchment management to reduce nitrate losses and fluvial loading. Careful land management and fertilizer use are necessary to avoid nitrate pollution in the karst agroecosystem, for example by timing fertilizer applications to allow for plant uptake of nitrate before rainfall can flush it from the soils into the karst and ultimately into catchment drainage.

The karst region in southwestern China is a typical region with fragile ecological environments, and the coordination of regional agricultural development and environmental protection faces enormous challenges. Based on the soil and hydrological characteristics of karst in southwestern China, this study summarized water-related environmental issues caused by agricultural activities in this karst region. Agriculture in the karst hills is more likely to cause soil and nutrient losses due to the fast hydrological flow through special karst structures with high permeability. Thus, this review emphasized the impacts of agricultural development on the riverine biogeochemical cycles of elements based on previous studies. Meanwhile, the carbon cycle is also strongly impacted by agricultural activities in this karst region due to enhanced carbonate weathering by nitric acid from the nitrification of ammonium. This weathering mechanism represents a net source of atmospheric CO2 and might impact regional and global carbon cycling in the Anthropocene. Based on the results summarized in this study, we advocate that in the future, better management of agricultural land, improvement of fertilizer use efficiency, and boosting of nutrient recycling rate should be taken into account for reducing nutrient losses and water quality deterioration. Targeted management of local agricultural practices along with guidance from scientific research results is needed to be devoted to sustainable development of agriculture and economies while protecting water environment.

In situ cosmogenic nuclides are widely employed to quantify topographic and geomorphic landscape evolution. However, few studies are devoted to investigating possibly unsteady denudation. In this work the denudation rates of five surface bedrock and one depth profile are measured using in situ cosmogenic 36Cl in different climate zones in China; cosmogenic 36Cl is a powerful proxy for the surface denudation processes of carbonate landscapes in different climatic gradients since carbonates are more sensitive to climate change than silicates. Compiling previous worldwide surface denudation studies in different gradients, we find that: (I) denudation rate increases systematically with mean annual precipitation (MAP) in arid climatic zones (MAP lower than ~700 mm yr−1) and is dominated by long-term climatic gradients; (II) humid climatic zone (MAP greater than ~700 mm yr−1) denudation rates are about constrained to 34.1 ± 11.7 mm kyr−1 by carbonate dissolution kinetics; and (III) denudation rate is also influenced by short-term physical erosion or abrupt erosive events. Accordingly, the reconstructed evolutionary history of the Guizhou depth profile results from either a relatively high denudation rate (55.5–4.4 +5.6 mm kyr−1) and long duration exposure (274–147 +120 ka), or an alternative a low denudation rate (0.8–0.8 +13.3 mm kyr−1) and a recent abrupt erosive event (13.0–1.6 +1.9 ka). These two possible solutions suggest that assumed long-term averaged denudation rate can conceal episodic erosion events. Given tectonic quiescence we propose that climate change might mainly control an erosive event during the last glacial termination (~14 ka), which also implies that caution should be taken when determining the denudation rate of a landscape where climate change and/or tectonic activity plays an important role.

The effect of dams on dissolved inorganic carbon (DIC) transport and riverine ecosystems is unclear in karst cascade reservoirs. Here, we analyzed water samples from a karst river system with seven cascade reservoirs along the Wujiang River, southwestern China, during one hydrological year. From upstream to downstream, the average concentration of DIC increased from 2.2 to 2.6 mmol/L and its carbon isotope composition (δ13CDIC) decreased from −8.0 to −10‰. Meanwhile, the air temperature (Ta) increased from 20.3 °C to 26.7 °C and 10 °C to 13.7 °C in the warm and cold seasons, respectively. The results suggest that a cascade of dams has a stronger effect on DIC dynamics and retention than a single dam. The good correlation between Ta/HRT (hydraulic retention time) and Δ[DIC] as well as Δ[δ13CDIC] mean that Ta and HRT affected the magnitude of the damming effect by altering changes in concentration of DIC and δ13CDIC in the reservoir compared to the inflowing water. In particular, daily regulated reservoirs with short retention times acted more like river corridors and had a smaller effect on carbon dynamics, so modulating retention time might be used reduce the effect of dams on the riverine ecosystem.

This paper investigated the sources and behaviors of sulfate in groundwater of the western North China Plain using sulfur and oxygen isotopic ratios. The groundwaters can be categorized into karst groundwater (KGW), coal mine drainage (CMD) and pore water (subsurface saturated water in interstices of unconsolidated sediment). Pore water in alluvial plain sediments could be further classified into unconfined groundwater (UGW) with depth of less than 30 m and confined groundwater (CGW) with depth of more than 60 m. The isotopic compositions of KGW varied from 9.3‰ to 11.3‰ for δ 34 S SO4 with the median value of 10.3‰ ( n = 4) and 7.9‰ to 15.6‰ for δ 18 O SO4 with the median value of 14.3‰ ( n = 4) respectively, indicating gypsum dissolution in karst aquifers. δ 34 S SO4 and δ 18 O SO4 values of sulfate in CMD ranged from 10.8‰ to 12.4‰ and 4.8‰ to 8.7‰ respectively. On the basis of groundwater flow path and geomorphological setting, the pore water samples were divided as three groups: (1) alluvial–proluvial fan (II 1 ) group with high sulfate concentration (median values of 2.37 mM and 1.95 mM for UGW and CGW, respectively) and positive δ 34 S SO4 and δ 18 O SO4 values (median values of 8.8‰ and 6.9‰ for UGW, 12.0‰ and 8.0‰ for CGW); (2) proluvial slope (II 2 ) group with low sulfate concentration (median values of 1.56 mM and 0.84 mM for UGW and CGW, respectively) and similar δ 34 S SO4 and δ 18 O SO4 values (median values of 9.0‰ and 7.4‰ for UGW, 10.2‰ and 7.7‰ for CGW); and (3) low-lying zone (II 3 ) group with moderate sulfate concentration (median values of 2.13 mM and 1.17 mM for UGW and CGW, respectively) and more positive δ 34 S SO4 and δ 18 O SO4 values (median values of 10.7‰ and 7.7‰ for UGW, 20.1‰ and 8.8‰ for CGW). In the present study, three major sources of sulfate could be differentiated as following: sulfate dissolved from Ordovician to Permian rocks (δ 34 S SO4 = 10–35‰ and δ 18 O SO4 = 7–20‰), soil sulfate (δ 34 S SO4 = 5.9‰ and δ 18 O SO4 = 5.8‰) and sewage water (δ 34 S SO4 = 10.0‰ and δ 18 O SO4 = 7.6‰). Kinetic fractionations of sulfur and oxygen isotopes as a result of bacterial sulfate reduction (BSR) were found to be evident in the confined aquifer in stagnant zone (II 3 ), and enrichment factors of sulfate–sulfur and sulfate–oxygen isotopes calculated by Rayleigh equation were −12.1‰ and −4.7‰ respectively along the flow direction of groundwater at depths of 60–100 m. The results obtained in this study confirm that detailed hydrogeological settings and identification of anthropogenic sources are critical for elucidating evolution of δ 34 S SO4 and δ 18 O SO4 values along with groundwater flow path, and this work also provides a useful framework for understanding sulfur cycling in alluvial plain aquifers.

To better understand the mechanisms that hydrological conditions control chemical weathering and carbon dynamics in the large rivers, we investigated hydrochemistry and carbon isotopic compositions of dissolved inorganic carbon (DIC) based on high-frequency sampling in the Wujiang River draining the carbonate area in southwestern China. Concentrations of major dissolved solute do not strictly follow the dilution process with increasing discharge, and biogeochemical processes lead to variability in the concentration-discharge relationships. Temporal variations of dissolved solutes are closely related to weathering characteristics and hydrological conditions in the rainy seasons. The concentrations of dissolved carbon and the carbon isotopic compositions vary with discharge changes, suggesting that hydrological conditions and biogeochemical processes control dissolved carbon dynamics. Biological CO2 discharge and intense carbonate weathering by soil CO2 should be responsible for the carbon variability under various hydrological conditions during the high-flow season. The concentration of DICbio (DIC from biological sources) derived from a mixing model increases with increasing discharge, indicating that DICbio influx is the main driver of the chemostatic behaviors of riverine DIC in this typical karst river. The study highlights the sensitivity of chemical weathering and carbon dynamics to hydrological conditions in the riverine system.

This study established the hydrochemistry and stable isotope variations in three lakes, namely brackish Zigetang Co, freshwater Cona and Ranwu lakes located in the central and southeastern Tibetan Plateau of China. Vertical profile fluctuations in the water column, such as temperature and dissolved oxygen (DO) concentration, displayed significant differences which were linked to the thermocline. The hydrochemistry of the three lakes showed that as the dominant anion, whereas Na+ is the main cation in Zigetang Co and Cona lake and Ca2+ is the prevailing cation in Ranwu lake. In Zigetang Co, K+ and Na+ concentrations decreased by 42 % from 1999 to 2012, caused by the enlargement of the lake area, documented by field investigations carried out in 1998, 2002, 2006 and 2012. The δ13CDIC and δ18OH2O values analysed from the three lakes varied from −6.0 to 2.0 ‰, and from −14.8 to −6.4 ‰, respectively. The closed Zigetang lake showed higher δ13CDIC and δ18OH2O values compared to those of the rivers, the semi-closed Cona and open Ranwu lakes. The δ13CDIC values of lake water in Zigetang Co were mainly controlled by CO2 exchange between lake water and atmosphere; the δ18OH2O values were dominated by the evaporation/freshwater input ratios.

We investigated the abundance of different picophytoplankton groups and the phytoplankton pigment ratio in relation to environmental factors such as nutrients and suspended solids along a salinity gradient in the Changjiang River Estuary. The average numbers of Synechococcus spp. (Syn) and picoeukaryotes (Euk) were (2.7 ± 5.1) ×103 and (1.1±1.4) ×103 cells mL−1, respectively. Prochlorococcus spp. (Pro) was only found in the high-salinity brackish water with the concentration of 3.0×103 cells mL−1. Syn and Euk numbers both tended to increase offshore and Syn showed a larger variation in cell abundance than Euk. The contribution of picophytoplankton to total phytoplankton biomass increased with increasing salinity and decreasing nutrient concentrations from the estuary to the open ocean. The response of different picophytoplankton groups to environmental variables was different. Water temperature was more important in its control over Euk than over Syn, while nutrients were more important in their influence over Syn than over Euk. Phytoplankton pigment ratios were different in the three different ecological zones along the salinity gradient (i.e., freshwater zone with 0–5 range, fresh and saline water mixing zone with 5–20 range, and high-salinity brackish water zone with 20–32 range), where three different phytoplankton communities were discovered, suggesting that phytoplankton pigment ratios can be considered as a complementary indicator of phytoplankton community structure in the Changjiang River Estuary.

To better understand chemical weathering and controlling processes in the Yalong River of the eastern Tibetan Plateau, this study presents major ion concentrations and stable isotopes of the dissolved loads. The isotopic compositions (δ13C-DIC, δ34S and δ18O-SO4) of the dissolved loads are very useful to quantify solute sources and define the carbon budget related with chemical weathering in riverine systems. The isotopic composition of sulphate demonstrates that most of the sulphate is derived from sulphide oxidation, particularly in the upper reach of the Yalong River. The correlations between δ13C-DIC, water chemistry and isotopes of sulphate, suggest that the carbon dynamics are mainly affected by carbonate weathering by sulphuric acid and equilibration processes. Approximately 13% of the dissolved inorganic carbon in the Yalong River originates from carbonate weathering by strong acid. The CO2 consumption rates are estimated to be 2.8 × 105 mol/km2/yr and 0.9 × 105 mol/km2/yr via carbonate and silicate weathering in the Yalong River, respectively. In this study, the influence of sulphide oxidation and metamorphic CO2 on the carbon budget is estimated for the Yalong River draining the eastern Tibetan Plateau.

The contents and stable S isotope ratio (δS) values of total S, organic S, SO-S, and total reduced inorganic S (TRS) in typical limestone soil and yellow soil were analyzed in this study to examine the general distributions of S forms and their δS values in soils in karst areas of southwest China. Under a similar level of acid deposition, the vertical profiles of the S forms and their δS values differed in limesto\ne soil and yellow soil, indicating the different geochemical responses of these soils to acid deposition. The deposited SO was retained as organic S in both soils. The depletion in S of TRS relative to SO and the parallel increasing δS values of TRS and SO indicate a bacterial reduction process of sulfate in both soils. The different extents of C-bonded S mineralization and organic sulfate transport explain the different vertical profiles of total S and organic S contents in both soils. Sulfate adsorption in limestone soil was negligible because of high pH values. Sulfate adsorption in yellow soil was another important S retention process in addition to biological S retention to form organic S and TRS because of low pH values. The effect of acid deposition on yellow soil appeared more serious because of the accumulation and leaching of deposited SO, which can result in soil acidification and accelerate the loss of basic cations from yellow soil. However, compared with yellow soil, limestone soil released more S into rivers by organic S mineralization after a large decrease in annual S deposition rate.

Excess nutrient (N and P) loads are recognized as the major cause of serious water quality problems in China. River systems play a very important role in nitrate (NO3 −) transportation and transformation in the aquatic environment. To understand and clarify the sources and processes affecting NO3 − in river basins, we have examined spatial and temporal variations of concentration and dual-isotopic composition of NO3 − in the dam-controlled Jialing River, a major tributary of the Yangtze River where land use is dominated by agriculture. Water samples were collected in July 2008 and February 2009 from the main channel of the Jialing River and its major tributaries. The δ15N and δ18O of NO3 − range from 1.5 to 11.0 ‰ (average 6.2 ‰) and −5.0 to 11.1 ‰ (average, 1.6 ‰), respectively. NO3 − isotope data and δ18O of water interpreted in combination with hydrological and chemical data suggest that most of the NO3 − input is from nitrification during the rainy season, and discharge of sewage and manure in the upper course and from cities accounts for much of the NO3 − load during the dry season. The construction of cascade dams has led to retention of Si and a decrease in the Si/N ratio, implying that assimilation and/or denitrification may significantly affect NO3 − in the dam area, as demonstrated by NO3 − and dissolved Si concentrations, and $$\updelta^{ 1 5} {\text{N}}_{{{\text{NO}}_{3} }}$$ and $$\updelta^{ 1 8} {\text{O}}_{{{\text{NO}}_{3} }}$$ values. This study indicates that dual-isotopic data can be used to identify NO3 − pollution sources and the processes NO3 − has undergone during its retention and transport in the watershed of the dam-controlled Jialing River.

To determine the impact of damming on the geochemical behavior of dissolved inorganic carbon (DIC) in the Wujiang River basin, field measurements and samples were collected semimonthly for a year. The surface waters of the reservoirs contained concentrations of chlorophyll a up to 5.6 times higher than the upstream river. Compared with the entering waters, the contributions of HCO3 − and dissolved CO2 to DIC decreased, and the contribution of CO3 2− to DIC and the carbon isotopic composition of DIC (δ 13CDIC) increased in the surface waters of the reservoirs, while in the waters released, the DIC species showed reverse geochemical behaviors. The δ 13CDIC ranged from −10.2 ‰ to 2.5 ‰, indicating that significant contributions were from carbonate weathering, photosynthesis, and respiration. After the damming of a river, the bioactivity of phytoplankton was enhanced, and this affected the geochemistry of DIC compared to an unimpacted river and δ 13CDIC can be used to discern these changes. High-frequency monitoring of river-reservoir systems is necessary to evaluate the efflux of CO2 and provide a better understanding of the carbon sinks and sources in the impounded river.

The Wujiang River is an important tributary to the Changjiang River that has been intensively impounded for hydropower exploitation. To understand the potential impact of reservoir construction on the riverine inorganic carbon transport, seasonal longitudinal sampling was conducted in four reservoirs Hongjiadu (HJD), Dongfeng (DF), Suofengying (SFY) and Wujiangdu (WJD) along the Wujiang River from April 2006 to January 2007. Results indicated that damming the river induced an obvious discontinuity of water chemistry in the warmer seasons. δ 13C of dissolved inorganic carbon (DIC) ranged from −3 to −11.4 ‰, likely as the results of photosynthesis, respiration and carbonate weathering. During periods of thermal stratification, the addition of CO2 from respiration to hypolimnion and the deep water release for hydropower generation led to higher pCO2 downstream, as well as 13C depletion in DIC and undersaturated to calcite. An estimate of DIC budget indicated that only DF reservoir was the sink for DIC while reservoirs HJD, SFY and WJD were the sources for DIC. However, when the retained water was taken into account, for the reason of water storage occurring mainly in HJD and DF, all reservoirs became the sources for DIC with exporting rates of 26.68, 7.97, 6.22 and 11.80 % for HJD, DF, SFY and WJD, respectively.

The concentrations of rare earth elements in the waters and suspended particles from two alkaline lakes in a carbonate drainage basin of the South China Karst region were determined via ICP-MS. Sequential chemical extraction experiments were conducted on the suspended matter to investigate water-particle interaction processes. Due to their high pH, the alkaline lakes have lower concentrations of dissolved rare earth elements than those reported for most other terrestrial surface waters of the world. Linear regressions between pH and the rare earth element (REE) concentrations over a wide pH range show a “three stage model,” implying the geochemical behavior of dissolved REEs in surface waters is mainly controlled by pH. Shale-normalized patterns of dissolved REEs mainly show a marked enrichment in heavy REEs (HREE), while acid-extracted and organic REEs mainly show convex patterns and the residual fractions have flat patterns. Distinct positive La anomalies were observed in the Lake Aha and its river waters, which also exhibit a very high Mn concentration, indicating severe redox and scavenging conditions. Both negative and positive Ce anomalies were clearly observed in the dissolved phase and extracted fractions of suspended particulate matter. The positive correlation of Ce anomalies with Mn indicates that redox reactions control these Ce anomalies.

The Liao River Basin is one of seven primary river Basins in China. The concentration of dissolved inorganic N (DIN), dual isotopes of NO 3 - using the denitrifier method, the N isotopes of NH 4 + and the N flux in the basin were determined to identify the sources of N and their transformation. The results show that NO 3 - ranges from 0.3 μmol/L to 1316 μmol/L. In general, NO 3 - is the dominant inorganic N species during both flow seasons, but the fraction of NO 3 - /DIN is variable and high NH 4 + is present in some waters. Samples collected from the up-stream portion of the Liao River typically had N isotope values of +8‰ during the high flow season. Most water samples had O isotope values of NO 3 - during the high flow season than the low flow season. The isotopic pattern of NO 3 - suggests that wastewater and soil organic N are the sources of NO 4 + during the high flow season, while wastewater is the main source during low flow season. It appears that no intense denitrification occurs in the river according to the isotopic and chemical data. The N flux of the Liao River system entering the Liao Dong Bay annually is nearly 7.0 × 104 tons, which amounts to 5.0% of the N from chemical fertilizers used in this basin.

For the first time, the river water geochemistry of the Songhuajiang Basin, the third largest river system in China, has been studied in order to understand chemical weathering and associated CO2 consumption rate in a mid- to cool temperate and monsoon-controlled climatic zone. The major ion compositions of the river waters are characterized by the dominance of Ca2+ and HCO 3 - , accounting for 46% and 74% of major cations and anions, respectively. The average total dissolved solids (TDS, 116 mg L−1) and total cation concentration (TZ+, 1388 μEq L−1) of the river waters are similar to those of global major rivers. The chemical weathering rates of carbonate, silicate and evaporites in the whole Songhuajiang Basin are estimated to be approximately 5.15, 2.23 and 0.40 t km−2 a−1, respectively. The total rock weathering rate for the whole Songhuajiang Basin is approximately 7.78 t km−2 a−1, which is at the lower end of the spectrum for global major rivers, and is comparable with that of the Amur and the Congo-Zaire River. The estimated CO2 consumption rates for the whole Songhuajiang Basin are 53.4 × 103 mol km−2 a−1 and 66.6 × 103 mol km−2 a−1 by carbonate and silicate weathering, respectively. As a sub-basin, the 2nd Songhuajiang has the highest (18.9 t km−2 a−1) while the Nenjiang River Basin has the lowest total rock weathering rate (5.03 t km−2 a−1), which indicates important controls of regional climate and lithology. Compared to the large rivers of China, total rock weathering rates increase from north to south, supporting the idea that the climate acts as major control on global chemical weathering. The CO2 consumption rate by silicate weathering within the whole Songhuajiang River Basin, though under mid- to cool temperate climate, is in the same order of magnitude as that of Huanghe (82.4 × 103 mol km−2 a−1) and is not much lower than that of Changjiang (112 × 103 mol km−2 a−1), which suggests that the role of Songhuajiang River weathering in long-term climate change cannot be neglected compared to those of the large rivers of China.

This study quantifies surface denudation of carbonate rocks by the first application of in-situ cosmogenic 36Cl in China. Concentrations of natural Cl and in-situ cosmogenic 36Cl in bare carbonates from Guizhou karst areas were measured with isotope dilution by accelerator mass spectrometer. The Cl concentration varied from 16 to 206 ppm. The 36Cl concentrations were in range of (0.8–2.4)×106 atom g−1, resulting in total denudation rates of 20–50 mm ka−1 that averaged over a 104–105 a timescale. The 36Cl-denudation rates showed roughly a negative correlation with the local mean temperature. This preliminary observation may suggest the variations of proportions of chemical weathering and physical erosion in denudation process, depending upon local climatic conditions.

The concentration characteristics, sources, and potential ecological risk assessment of 16 PAHs were investigated in the surface water from the Songhua River Basin, Northeast China. A total of 48 river water samples, including 16 from the main streams and 32 from the tributaries, were collected. Samples were separated into dissolved phases and suspended particle matter (SPM) via filtration with 0.47 μm glass fiber filters. Each phase was analyzed for PAHs. The total PAH concentration in the dissolved phase in the water ranged from 32.5 to 108 ng L−1 and from 0.3 to 62.3 μg g−1 (dry weight) in the suspended particle matter (SPM). The total PAH concentration in the main stream was lower than in the tributaries; the volume of annual runoff of rivers had a significant effect on the ƩPAH in the rivers. The 2- and 3-ring PAHs dominated in both the dissolved phase and SPM, indicating a relatively recent local source of PAHs in the study area. The concentrations of PAHs in the Songhua River Basin are lower when compared with the values previously reported in the literature from other rivers around the world. The sources of PAHs were assessed by diagnostic ratios and principal component analysis (PCA), and the ecological risk of the PAHs was assessed based on the risk quotient (RQ). The diagnostic ratios and PCA indicated that the main sources of PAHs originated from pyrogenic and petrogenic sources, and pyrogenic sources had a greater impact. The ecological risk assessment indicated that the PAHs presented low ecosystem risk in the Songhua River Basin.

We present major ion compositions for water samples from Jinshajiang, Lancangjiang, and Nujiang drainage basins of China, collected in a water-rich period. This was done to determine natural chemical weathering rates on the eastern Himalayan and Qinghai-Tibet Plateau (HQTP), where anthropogenic impacts are considered small. The major ion distribution of the mainstream samples primarily reflects the weathering of carbonates, which accounts for ~46 % of total cations in the samples of Lancangjiang and Nujiang. Evaporite dissolution prevailed in the mainstream samples of Jinshajiang, as evidenced by high total dissolved solids (TDS) (364–479 mg/L) and Cl, SO4, and Na-dominant major element composition. Silicate weathering contributed

Epikarst water, which is one of the most important water resources in karst mountain areas, is extremely sensitive to mining activities. Acid mine drainage (AMD) with high levels of heavy metals can degrade the water quality. A typical coalfield basin was chosen to research the migration process of heavy metals. It was found that the chemical compositions of the stream water in the research field were controlled by the dissolution of carbonate rocks or/and the weathering and oxidation of pyrite in the mining area. Excluding a few sites in the mining area, As(V) was dominant species of arsenic in the form of H2AsO4 − or HAsO4 2− in the research field. Based on the mass balance concept, it was found that fluxes of As, Zn, Cu and Cd in water from the mining area (site 17) affected by AMD were 18, 871, 281 and 12 kg year−1, respectively. Also, concentrations of Cd, Zn, As and Cu in the stream water decreased along the flow, because these ions deposited from the water to the stream bed as the redistribution processes in environment.

Water samples were collected for 23 different stations along a cross section profile of an estuary extending over to adjacent sea. The collected water samples were filtered and analyzed for major–minor ions and strontium isotope using the standard procedure to understand the geochemical behaviors of major and minor elements. The normalized values indicated that all riverine elements were entering to adjacent coastal sea with some significant variations at the estuary. The seawater dilution and regression lines explain about the overall patterns for seven elements. Removal processes were detected on calcium, magnesium, strontium and sulfate in the estuarine region. No significant mineral precipitation observed to release magnesium with respect to calcium. Minor variations of strontium and sulfate ions could be attributed to the presence of organic matter in the study area. Comparing seven elements with total suspended matters revealed that the total suspended matters played crucial role in either adsorption or absorption of all the elements in estuary before it reaches to coastal sea. Mixing patterns of strontium isotope showed minimal non-conservative with an evidence of active geochemical process in the estuary.