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Quantifying the gross rates of individual nitrogen (N) processes is critical for understanding the availability, retention and loss of N and its eco-environmental impacts in agricultural ecosystems. Here, we carried out a 15N tracing study to quantify the influence of soil moisture on the gross rates of ten different N processes in two intensively managed fluvo-aquic soils. Results showed that the gross N mineralization rates were insensitive to changes in soil moisture, ranging from 40 to 120% water-filled pore space (WFPS). Contrarily, the gross ammonium (NH4+) immobilization rates increased exponentially with elevated soil moisture. Specifically, under high soil moisture conditions (i.e., 90–120%WFPS), the gross NH4+ immobilization rates (4.04 ± 0.83 and 0.88 ± 0.28 mg N kg− 1d− 1 for the two soils, respectively) were nearly four times higher than those under medium or low moisture conditions (i.e., 40–80%WFPS). Meanwhile, the high WFPS reduced the gross autotrophic nitrification rates (5.92 ± 2.15 and 12.31 ± 3.83 mg-N kg− 1d− 1 for the two soils, respectively) to only one-third to one-half of those that were observed under medium or low WFPS. By contrast, the rates of nitrate (NO3−) immobilization increased in one soil whereas they decreased in another under high moisture conditions, and the other N processes (including heterotrophic nitrification and dissimilatory nitrate reduction to ammonium (DNRA)) were negligible throughout the different WFPS. Overall, our results suggest that under highly saturated conditions, the increase in microbial NH4+ immobilization and decrease in autotrophic nitrification are critical for N retention in the fluvo-aquic soils. These findings provide valuable insights into potential alterations in soil N retention or loss under future climate change scenarios, where more intensive irrigation and extreme rainfall events are anticipated. [ABSTRACT FROM AUTHOR]

• Seawater intrusion and weathering determined water quality of coastal zone (CZ). • Dam regulation in CZ rivers affected water chemical components and nitrogen cycle. • N fate in the weak coastal hydrological zone rivers was driven by microorganisms. • Sewage and manure sources were major nitrate contributors in the studied CZ. Coastal zones (CZ) are ecologically and environmentally significant, and it is thus critical to study the interactions among different types of natural CZ waters for better understanding biogeochemical processes. Water samples (n = 101) were analyzed for multiple stable isotopes (δ18O-H 2 O, δD-H 2 O, δ15N-PON, δ15N-NO 3 −, and δ18O-NO 3 −) in seawater, river water, reservoir water and groundwater at Tianjin CZ to demonstrate the spatial variations in the CZ aqueous environment and to identify key influencing processes factors of the N geochemical cycle. This study confirmed that weathering dominated upstream water properties, whereas seawater intrusion determined the downstream and midstream water chemical components, where the seawater fraction was 44% and 11%, respectively. Evaporation and precipitation processes were active across the whole CZ area, but their impacts on water chemical components were less significant than seawater intrusion and weathering. Dam regulation in CZ rivers has significantly affected water chemical components and the nitrogen cycle. The isotopic evidence indicated that bacterioplankton and phytoplankton were the primary forms of PON. The dual nitrate isotopes revealed that animal manure and industrial sewage contributed the leading nitrate to river water. The spatial variation of their contribution was quantitated (from upstream to midstream and downstream: 62%, 91% and 83%, respectively). Considering the potential isotopic fractionation of nitrification reduction from upstream to downstream, 39%, 61% and 57%, respectively. This study proposes a quantitative framework for detecting CZ areas with similar hydrodynamic conditions and climate characteristics found at the Tianjin CZ, which has important implications for CZ water management and environmental protection policies. [ABSTRACT FROM AUTHOR]

Abstract: The dual isotopic compositions of dissolved in aquatic systems are commonly used to ascertain sources and possible biogeochemical processes. In this study, the physical parameters, major anions and isotopic compositions of in water samples from Changjiang River (Nanjin) to the East Sea in Changjiang Estuary were determined. The salinity ranged from 0‰ to 32.3‰ in the estuary water samples. The concentrations and δ18O–H2O values followed the salinity variations from freshwater to seawater, which indicated that mixing processes might be a major factor involved in the distribution of water and solutes. The contents and isotopic compositions of suggested that atmospheric deposition, evaporite dissolution and sulphide oxidation were the major sources of dissolved in the freshwater of Changjiang River. In addition, the mixing model calculated by contents and isotopic compositions of indicated that the mixing of freshwater and sea water was the major factor involved in distribution in Changjiang Estuary. However, slightly elevated δ18O–SO4 values were observed in the turbidity maximum zone, which suggested that biological processes might affect the O isotopic compositions of there. [Copyright &y& Elsevier]

• Water chemistry, δ13C DIC and δ34S SO4 were investigated in the Jialing River. • Sulfide oxidation played an important role in carbon cycling. • Hydrologic variability impacts chemical weathering and carbon cycling. The negative feedbacks between chemical weathering and climate change were hypothesized to regulate the atmospheric CO 2 over short-term and geologic timescales. In this study, we collected temporal water samples from the Jialing River, and analyzed water chemistry, stable isotopic compositions of dissolved inorganic carbon (δ13C DIC) and sulfur isotope of sulfate (δ34S SO4) to investigate the effects of hydrological changes on chemical weathering. The results of the inverse model based on the Monte Carlo method showed that major cations were mainly derived from carbonate (63.9%) and silicate (12.0%) weathering, and sulfuric acid plays an important role in carbon biogeochemical processes. Based on water chemistry, δ34S SO4 and δ13C DIC , the carbon biogeochemical processes were investigated, showing the influence of secondary processes. We estimated the weathering rates of carbonate (19.7 t/km2yr) and silicate (3.9 t/km2yr) in the Jialing River, and then estimated CO 2 consumption flux by carbonate weathering (24.5 t/km2yr), silicate weathering (8.1 t/km2yr), and total CO 2 consumption flux (27.5 t/km2yr) deducting the influence of pyrite oxidation. Our research showed the significant role of pyrite oxidation in carbon cycling. This study highlighted the impacts of hydrological variabilities on the generation and transport of solutes, which have significant implications for understanding carbon cycling under ongoing climate change. [ABSTRACT FROM AUTHOR]

Summary To understand the sources and transformations of nitrate in the Songhua River basin, which is one of seven largest river basins in China, the concentration of dissolved nitrogenous species, nitrogen and oxygen isotopes of NO 3 − , nitrogen isotopes of NH 4 + , and stable isotopes of water were determined in this study. Low NO 3 − concentrations and a high dissolved organic nitrogen/total dissolved nitrogen ratio (DON/TDN) were observed in the Nen River and other rivers originating from the mountains, which are covered by forest. NO 3 − and DON were the major nitrogenous compounds in aquatic systems, accounting for the TDN being about 90% during high flow season and about 85% during low flow season, respectively. The nitrogen efflux for the entire basin was estimated to be approximately 1.17 × 10 5 tons/yr, which represents an annual N output of 0.21 ton/(km 2 yr). The majority of the δ 18 O-NO 3 − values were between −4‰ and 4‰, reflecting nitrification. During the high flow season, the isotopic compositions of NO 3 − and the water chemistry suggest that NO 3 − in the Nen River was mainly derived from soil organic nitrogen (SON), whereas NO 3 − in the Songhua River originated from organic nitrogen, nitrogenous fertilizers and sewage waters. NO 3 − in the low flow season samples generally originates from SON and sewage waters. Moreover, the calculated loss of nitrate via the mass budget in rivers, together with isotopic values and water chemistry confirm that denitrification occurs during the high flow season, especially in the Songhua River. This study suggests that the mass calculation and isotopic proof provide a better understanding for riverine N budget and biogeochemical processes. [ABSTRACT FROM AUTHOR]

[Display omitted] • δ13C, δ15N, and δ18O were analyzed to reveal carbon–nitrogen coupled absorption. • Stability regulation mechanism of karst reservoir was indicated by diel monitoring. • The stability promotes the biological carbon pump development of karst reservoir. • Biological carbon pump caused carbon burial in karst reservoir. While river damming has been extensively investigated, there remains unclear in the diel biogeochemical processes and carbon control mechanisms in karst reservoirs, under the influence of the biological carbon pump (BCP) effect. We investigated the diel variation of Hongjiadu (HJD) and Wujiangdu (WJD) reservoirs, which exhibit typical periodic thermal stratification, in the Wujiang River located in Southwest China. We found that diel variation of dissolved inorganic carbon (DIC) (HJD: 1668.6 ± 10.4 µmol/L; WJD: 1777.9 ± 31.5 µmol/L), δ13C DIC (HJD: −3.1 ± 0.1 ‰; WJD: −4.6 ± 0.4 ‰), and other parameters in the lentic zones were relatively stable. Moreover, the Revelle factor in the lentic zones (HJD: 44.3-49.0; WJD: 44.3-53.9) were substantially higher than those of the fluvial zones (HJD: 24.4-33.4; WJD: 14.2-35.1). The stable diel variations indicate that the HJD and WJD reservoirs may have distinct stability regulatory mechanisms. In the lentic zones, δ13C DIC , nitrogen–oxygen isotope (δ15N and δ18O), and the correlation of C-N indicated that the conversion of DIC and NO 3 – is primarily influenced by primary production, and there was coupled absorption of carbon and nitrogen nutrients during photosynthesis. Meanwhile, the C/N weight ratio (6.0-10.1) and the δ13C POC (−30.0 ‰ to −24.7 ‰) also revealed a gradual transition from soil organic matter (OM) in the fluvial zone to phytoplankton source in the intermediate-lentic zone. Thus, two reservoirs had a significant BCP effect and converted a significant amount of DIC to autochthonous organic carbon (AOC) burial in the lentic zones. The BCP effect in subtropical deep karst reservoirs buried lots of carbon, increased carbon sequestration and decreased CO 2 emissions in the lentic zone. Simultaneously, the stability of reservoirs promotes BCP effect and intensifies carbon sequestration, which is of great significance for the study of the global carbon sources-sinks pattern. [ABSTRACT FROM AUTHOR]

• Unveiling the dissolved inorganic carbon cycle in a karst reservoir through hydrodynamic modeling and δ13C. • The DIC retention capacity is more pronounced under weak hydraulic conditions in HJD. • Significant CO 2 emissions during periods of intense hydrodynamics necessitate close monitoring. • Quantification of DIC flux across diverse hydrodynamic scenarios in a deep subtropical reservoir. • The method (hydrodynamic model and δ13C) is applicable to karst canyon-type reservoir worldwide. Dam construction significantly impacts river hydrodynamics, subsequently influencing carbon biogeochemical processes. However, the influence of hydrodynamic conditions on the migration and transformation of Dissolved Inorganic Carbon (DIC) remains uncertain. To bridge this knowledge gap, we integrated hydrochemistry, isotopic composition (δ13C DIC), and a hydrodynamic model (CE-QUAL-W2) to examine the distinctions, control mechanisms, and environmental effects of DIC biogeochemical processes in a typical large and deep reservoir (Hongjiadu Reservoir) under different hydrodynamic conditions. We evaluated hydrodynamic alterations through the Schmidt stability index and relative water column stability. The analysis disclosed that during weak hydrodynamics periods, the energy necessary for complete mixing the surface and deep water was 34 times higher (3615.32 J/m2 vs.106.86 J/m2), and stability was 13 times greater (312.96 vs. 24.69) compared to periods of strong hydrodynamics. Additionally, the spatiotemporal heterogeneity of DIC concentrations (1.4 % to -9.1 %) and δ13C DIC (-1.7 % to -19.5 %) from the dry to wet seasons reflected disparities in DIC control mechanisms under varied hydrodynamic conditions. Based on model simulations, our calculations indicate that during weak hydrodynamics periods, the enhancement of the biological carbon pump effect resulted in substantial sequestration of DIC, reaching up to 379.6 t-DIC·d−1 in the water. Conversely, during strong hydrodynamics periods, DIC retention capacity decreased by 69.2 t·d−1, resulting in reservoir CO 2 emissions of 22.7 × 104 t, which were more than 7 times higher than during weak hydrodynamics periods (3.2 × 104 t). Our findings emphasize the discernible impact of hydrodynamic conditions on reservoir biogeochemical processes related to DIC. Considering the increasing construction of reservoirs globally, understanding and controlling hydrodynamic conditions are crucial for mitigating CO 2 emissions and optimizing reservoir management. [Display omitted] [ABSTRACT FROM AUTHOR]

Excessive levels of NO 3 - can result in multiple eco-environmental issues due to potential toxicity, especially in coastal areas. Accurate source tracing is crucial for effective pollutant control and policy development. Bayesian models have been widely employed to trace NO 3 - sources, while limited studies have utilized optimized Bayesian models for NO 3 - tracing in the coastal rivers. The Bohai Rim is highly susceptible to ecological disturbances, particularly N pollution, and has emerged as a critical area. Therefore, identification the N fate and understanding their sources contribution is urgent for pollution mitigation efforts. In addition, understanding the influenced key driven factors to source dynamic in the past ten years is also implication to environmental management. In this study, water samples were collected from 36 major river estuaries that drain into the Bohai Sea of North China. The main transformation processes were analyzed and quantified the sources of NO 3 - using a Bayesian stable isotope mixing model (MixSIAR) with isotopic approach (δ 15N-NO 3 - and δ 18O-NO 3 -). The overall isotopic composition of δ 15N-NO 3 - and δ 18O-NO 3 - in estuary waters ranged from −0.8–19.3‰ (9.3 ± 4.6‰) and from −7.1–10.5‰ (5.0 ± 4.3‰), respectively. The main sources of nitrate in most river estuaries were manure & sewage, and chemical fertilizer, while weak denitrification and mixed processes were observed in Bohai Rim region. A temporal decrease in the nitrogen load entering the Bohai Sea indicates an improvement in water quality in recent years. By incorporating informative priors and utilizing the calculated coefficients, the accuracy of sourcing results was significantly improved. This study highlighted the optimized MixSIAR model enhanced its accuracy for sourcing analysis and providing valuable insights for policy formulation. Future efforts should focus on improving management strategies to reduce nitrogen into the bay. [Display omitted] • N pollution is high in southern rivers of Bohai Rim due to anthropogenic activities. • Effective management has led to decrease in N pollution levels over past ten years. • Sewage & manure and fertilizer contributed three quarters N sources to the study rivers. • Considering fractionation effect and informative prior can enhance precision of source. [ABSTRACT FROM AUTHOR]

Pharmaceuticals and personal care products (PPCPs) are emerging contaminants that have raised urgent environmental issues. The dissolved organic matter (DOM) plays a pivotal role on PPCPs' migration and transformation. To obtain a comprehensive understanding of the occurrence and distribution of PPCPs, a seasonal sampling focused on the riverine system in coastal zone, Tianjin, Bohai Rim was conducted. The distribution and transformation of thirty-three PPCPs and their interaction with DOM were investigated, and their sources and ecological risks were further evaluated. The total concentration of PPCPs ranges from 0.01 to 197.20 μg/L, and such value is affected by regional temperature, DOM and land use types. PPCPs migration at soil-water interface is controlled by temperature, sunlight, water flow and DOM. PPCPs have a high affinity to the protein-like DOM, while the humus-like DOM plays a negative influence and facilitates PPCPs' degradation. It is also found that protein-like DOM can represent point source pollution, while humus-like substances indicate non-point source (NPS) emission. Specific PPCPs can be used as markers to trace the source of domestic discharge. Additionally, daily use PPCPs such as ketoprofen, caffeine and iopromide are estimated to be the main risk substances, and their ecological risk varies on space, season and river hydraulic condition. [Display omitted] [ABSTRACT FROM AUTHOR]

Agricultural soils are a major source of anthropogenic N 2 O, but their N 2 O emission estimates are highly uncertain, mainly due to the complexity of nitrogen (N) processes. Most soil N models include only primary N processes such as nitrification and denitrification, which limits their ability to realistically simulate N transformations in soils and accurately estimate N 2 O emissions from soils. This study introduces a Microbial-Explicit Model incorporating Comprehensive Nitrogen processes (MEMCN) to evaluate and quantify the influences of various N processes on the production of N 2 O as well as NO and N 2 , including nitrification, denitrification, anaerobic ammonium oxidation (ANAMMOX), dissimilatory nitrate reduction to ammonium (DNRA), mineralization, and microbial assimilation (i.e., growth) and death. The MEMCN was evaluated in laboratory experiments using agricultural soils with different levels of N additions under anaerobic and aerobic conditions, and reproduced well the dynamics of NH 4 +, NO 3 −, NO 2 −, NO, N 2 O, and N 2. After nitrification and denitrification, ANAMMOX and assimilation were found to be most important in controlling N transformations in agricultural soils. ANAMMOX directly increased N 2 emissions by 139% at the beginning of the simulations (i.e., 48 h) under anaerobic conditions, while microbial assimilation indirectly reduced NO, N 2 O, and N 2 emissions by 88%, 54%, and 58%, respectively, at the end of the simulations (i.e., 336 h) under aerobic conditions. Correspondingly, the biomass of ANAMMOX bacteria increased significantly at the beginning of the simulations under anaerobic conditions, while the biomass of nitrite oxidizing bacteria increased substantially under aerobic conditions. In contrast, DNRA, mineralization and microbial death had minor effect on soil N transformations, and the biomass of DNRA bacteria and heterotrophs did not change significantly during the simulations. Our study shows that it is necessary to include ANAMMOX and microbial assimilation in soil N models, while explicit simulation of microbial biomass dynamics may only be necessary if microbial biomass pools change significantly. • Develope a Microbial-Explicit Model incorporating Comprehensive N processes. • Quantify contributions of individual N processes to gaseous N production. • ANAMMOX increased N 2 produciton under aerobic and anaerobic condtions. • Assimilation reduced NO, N 2 O, and N 2 emissions under aerobic condtions. • Micoribal biomass should be explicitly expressed as they change substantially. [ABSTRACT FROM AUTHOR]

Abstract: Greenhouse gas emissions from hydroelectric dams have recently given rise to controversies about whether hydropower still provides clean energy. China has a large number of dams used for energy supply and irrigation, but few studies have been carried out on aquatic nitrous oxide (N2O) variation and its emissions in Chinese river-reservoir systems. In this study, N2O spatiotemporal variations were investigated monthly in two reservoirs along the Wujiang River, Southwest China, and the emission fluxes of N2O were estimated. N2O production in the reservoirs tended to be dominated by nitrification, according to the correlation between N2O and other parameters. N2O saturation in the surface water of the Wujiangdu reservoir ranged from 214% to 662%, with an average fluctuation of 388%, while in the Hongjiadu reservoir, it ranged from 201% to 484%, with an average fluctuation of 312%. The dissolved N2O in both reservoirs was over-saturated with respect to atmospheric equilibrium levels, suggesting that the reservoirs were net sources of N2O emissions to the atmosphere. The averaged N2O emission flux in the Wujiangdu reservoir was 0.64 μmol m−2 h−1, while it was 0.45 μmol m−2 h−1 in the Hongjiadu reservoir, indicating that these two reservoirs had moderate N2O emission fluxes as compared to other lakes in the world. Downstream water of the dams had quite high levels of N2O saturation, and the estimated annual N2O emissions from hydropower generation were 3.60 × 105 and 2.15 × 105 mol N2O for the Wujiangdu and the Hongjiadu reservoir, respectively. These fluxes were similar to the total N2O emissions from the reservoir surfaces, suggesting that water released from reservoirs would be another important way for N2O to diffuse into the atmosphere. It can be concluded that dam construction significantly changes the water environment, especially in terms of nutrient status and physicochemical conditions, which have obvious influences on the N2O spatiotemporal variations and emissions. [Copyright &y& Elsevier]

The release of biospheric organic matter (OM) stored in the humus-rich black soils of Northeast China is highly susceptible to permafrost thaw and agriculturally induced erosion processes, and plays a disproportionate role in the global carbon cycle. However, the perturbations of global change and anthropogenic activities on riverine export of particulate organic carbon (POC) in the high-latitude agricultural areas remain poorly constrained. In the present study, this knowledge gap was filled by identifying the provenances of particulate organic matter (POM) and the erosional flux of POC from the rivers draining Northeast China. The elemental (POC%, PON% and C/N ratio) and isotopic (δ13C and δ15N) compositions of POM in suspended particulate matter (SPM) from the rivers in Northeast China (the Songhua River (SRB) and Liao River basins (LRB)) were analyzed. The results showed that during the wet season, the δ13C and δ15N values of POM in SPM were −25.8 ± 1.2‰ and 6.6 ± 2.2‰ respectively. Elemental and isotopic characteristics of the SPM samples and potential sources indicated that the sources of POM differed significantly among different sampling periods and sites. During the wet season, Soil OM was the primary POM contributor. Compared to the SRB, autochthonous OM made relatively larger contributions to POM in the LRB. During the dry season, for the SPM samples mainly from the LRB, the δ13C and δ15N values of POM were −22.7 ± 4.3‰ and 3.1 ± 2.4% respectively, suggesting that effluent detritus was the predominant source. The flux and yield of SPM revealed the seasonal and spatial variations of physical erosion rate that controls POC export. Seasonally, up to 61% of the annual SPM load and 58% of the annual POC flux of the SRB occurred in May and August due to thawing processes and increasing precipitation. Spatially, the lower reaches of the SRB had the highest SPM yield and contributed more than half of the annual SPM load of the SRB, likely attributable to the high intensity of agricultural activities. Globally, the POC% in SPM and POC yield of the SRB were larger than a series of the world's largest rivers under a given SPM condition, suggesting the high sensitivity of terrestrial OM export to erosion. These findings highlight the perturbation and mobilization of terrestrial OM in Northeast China under intensive agricultural activities and ongoing global climate change. • Sources of particulate organic matter (POM) were identified by C and N isotopic approach. • Soil and effluent detritus were major contributors to POM in suspended particulate matter (SPM). • Thawing processes in May resulted in the export of large amounts of SPM and POM. • Land use pattern was closely related to elemental and isotopic compositions of POM. • High POM content of SPM and high sensitivity of POC yield to erosion were observed. [ABSTRACT FROM AUTHOR]

The photo-ammonification process plays a crucial role in the transformation of dissolved organic nitrogen (DON) to dissolved inorganic nitrogen (DIN). However, previous studies have primarily focused on DON biotransformation than on abiotic processes. This study investigated the photo-ammonification process of nine model low molecular weight (LMW) DON molecules (e.g., amino acids, nucleotides, and urea) under the influence of different light sources. The results showed that photo-ammonification of model DON was mainly induced by UV light, while negligible contribution by visible light was found. Depending on their molecular structures, amino acids yielded different ammonia amounts, whereas negligible photo-ammonification was observed for nucleotides and urea. As for the reactive species, OH promoted ammonia yields of all the model amino acids; 3CDOM⁎ contributed to the photo-ammonification of six amino acids; 1O 2 only had a positive impact on ammonification of tryptophan, histidine, and tyrosine; and CO 3 − accelerated ammonia generation from histidine and methionine. In natural water samples, tryptophan, tyrosine, histidine, and methionine generated significant ammonia. OH and 1O 2 were speculated as the contributing reactive species based on kinetic studies as well as significant fluorescent humic-like and tyrosine-like substances degradation in irradiated samples compared to the raw samples characterized by the EEM-PARAFAC analysis. The negative linear correlations between photo-ammonification rates and the E LUMO –E HOMO of the amino acids emphasized the importance of the role of the molecular structure. Overall, these results revealed the LMW DON photo-ammonification mechanism in sunlit surface waters and highlighted its significance in the nitrogen biogeochemical cycle as well as water quality management. Unlabelled Image • Aromatic amino acids (AAs) underwent photo-ammonification by UV irradiation. • OH accelerated photo-ammonification of all the targeted AAs. • 3CDOM⁎, 1O 2 , and CO 3 − play different roles in AA photo-ammonification. • AA photo-ammonification varied in different natural water samples. • Ammonia production was negatively correlated with E LUMO –E HOMO of AAs [ABSTRACT FROM AUTHOR]

• Agricultural ditches were significant sources of GHGs. • Ditches adjacent to farmlands observed high GHG concentrations and emissions. • Nutrient input was the primary driver stimulating GHG production and emissions. • GHG emissions from agricultural ditches should be incorporated into regional and global estimations. Agricultural ditches are pervasive in agricultural areas and are potential greenhouse gas (GHG) hotspots, since they directly receive abundant nutrients from neighboring farmlands. However, few studies measure GHG concentrations or fluxes in this particular water course, likely resulting in underestimations of GHG emissions from agricultural regions. Here we conducted a one-year field study to investigate the GHG concentrations and fluxes from typical agricultural ditch systems, which included four different types of ditches in an irrigation district located in the North China Plain. The results showed that almost all the ditches were large GHG sources. The mean fluxes were 333 μmol m-2 h-1 for CH 4 , 7.1 mmol m-2 h-1 for CO 2 , and 2.4 μmol m-2 h-1 for N 2 O, which were approximately 12, 5, and 2 times higher, respectively, than that in the river connecting to the ditch systems. Nutrient input was the primary driver stimulating GHG production and emissions, resulting in GHG concentrations and fluxes increasing from the river to ditches adjacent to farmlands, which potentially received more nutrients. Nevertheless, the ditches directly connected to farmlands showed lower GHG concentrations and fluxes compared to the ditches adjacent to farmlands, possibly due to seasonal dryness and occasional drainage. All the ditches covered approximately 3.3% of the 312 km2 farmland area in the study district, and the total GHG emission from the ditches in this area was estimated to be 26.6 Gg CO 2 -eq yr−1, with 17.5 Gg CO 2 , 0.27 Gg CH 4 , and 0.006 Gg N 2 O emitted annually. Overall, this study demonstrated that agricultural ditches were hotspots of GHG emissions, and future GHG estimations should incorporate this ubiquitous but underrepresented water course. [Display omitted] [ABSTRACT FROM AUTHOR]

• A high wet N deposition rate was observed in a study of a karst agricultural area. • Agriculture-derived NH 4 +-N contributed more than 55 % of total wet N deposition. • Isotopic modeling showed major contributor of NO 3 − is from farmland soil emission. Nitrogen (N) deposition plays a key role in ecosystem function as one of the major N sources for natural vegetation, particularly in karst agricultural areas with thin soil cover, which drive the karst N fate via rainwater. To understand the seasonal and spatial variation in nitrogen deposition and to identify the major sources of nitrate in wet deposition in a karst agricultural area (Houzhai Catchment) in southwestern China, two sites with different land use were selected to assess wet and dry deposition for one year. Houzhai village (HZV) is an area highly influenced by agriculture, whereas Muzhu reservoir (MZR) is a more pristine environment with less anthropogenic influence. Nitrogenous species and dual nitrate isotopes were analyzed. The results showed that agriculture-derived NH 4 + was the major contributor of annual total wet N deposition (>55 %). The contribution of NH 4 + to wet N deposition was 1.63 times higher than that of NO 3 − and dissolved organic nitrogen (DON). The annual nitrogen deposition in this study was approximately twice as much as the average wet N deposition over China, while lower dry N deposition relative to other Chinese monitoring sites was observed. The δ15N-NO 3 − showed a seasonal trend of negative summer values and positive winter values, which were primarily controlled by the variations in NO x emission sources. Seasonal variation in δ18O-NO 3 − was mainly controlled by NO x oxidation pathways and showed a similar trend to δ15N-NO 3 −. The contributions from four endmembers (coal combustion, vehicle exhaust, biomass burning, and soil emission) were calculated using a stable isotope mixing model. Contributions show a clear seasonal variation (except vehicle exhaust), with the four sources accounting for 20.0 %, 25.6 %, 22.9 % and 31.5 % respectively (annual mean probability estimate, AMPE) at HZV, and 19.0 %, 27.8 %, 23.2 % and 30.0 % (AMPE) at MZR. Isotopic evidence determined agricultural soil emission is a major contributor to rainwater during the summer growing season, which can significantly impact the agricultural ecosystems. [ABSTRACT FROM AUTHOR]

Agricultural land in karst systems can pollute water courses, with polluted waters travelling quickly to and through the sub-surface. Understanding how rapidly nitrate moves within the highly-transmissive karst critical zone (from soils to aquifers) is limited by low resolution data. To understand nitrate behavior and its controls, we deployed sensor technology at five sites to generate autonomously high-resolution time series of discharge and NO 3 −–N, which is the major nitrogenous component, in a farmed karst catchment in Southwestern China. The [NO 3 −–N] time series exhibited rapid response to rainfall-induced increases in discharge and a large magnitude in [NO 3 −–N], from 0.72 to 16.3 mg/L across five sites. However, the magnitude of NO 3 −–N response at each site was varied during rainfall events (wet season) and dry season. The highest mean [NO 3 −–N] and normalized annual fluvial export occurred in a headwater catchment with a developed karst aquifer system. Seasonal variation in NO 3 −–N export occurred in response to source availability, most notable in catchments with valley agriculture: in the wet season up to 94% of nitrate was exported from the headwater catchments within two months, but at the larger catchment scale, over the 6 month wet season, only 61% of total export occurred. At the larger catchment scale, [NO 3 −–N] were lower due to buffering by the karstic aquifer network. From the time series we observe little decrease in [NO 3 −–N] as discharge decreases in the dry season, indicating the karst aquifers are chronically-polluted with nitrate through slow flow pathways. Unlabelled Image • Sensor technology in the karst critical zone offers high resolution NO 3 − dynamics. • Hydrological and seasonal NO 3 − responses were observed at multiple spatial scales. • NO 3 − export varied by season in response to sources availability and karst aquifer. • Sensor technology revealed chronic aquifer NO 3 − pollution. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A novel naphthyridyl derived Schiff-base 1 was designed and synthesized. • Significant fluorescence enhancement at 504 nm was observed with addition of Zn2+ to 1 solution. • High selectivity and sensitivity of 1 towards Zn2+ over other metal ions were obtained. • The mechanism for the responses of 1 to Zn2+ was investigated. Abstract In this study, bearing 4-methyl-7-acetamide-1,8-naphthyridyl group as the fluorophore and the receptor, we designed and synthesized a new-type Schiff-base ligand 1 which was identified as a Zn2+ fluorescent probe. The excellent selectivity and high sensitivity of this as-synthesized fluorescent probe 1 towards Zn2+ over other various biogenic metal ions were observed, for that only Zn2+ induced a drastic enhancement by about 63-fold in intensity of fluorescence emission at 504 nm, and the limit of detection (LOD) could reach 7.52 nM. Moreover, the formation of a 2:1 complex between this probe 1 and Zn2+ was determined, and the perfect invertibility and renewability of this probe 1 for sensing Zn2+ were also demonstrated. As a result, the practical applications of 1 were broadened for sensing and monitoring Zn2+ environmentally and biologically. [ABSTRACT FROM AUTHOR]

In order to better understand the relative importance of hydrologic variation and anthropogenic disturbance and their complex interactions within the trace elemental geochemical cycle, water samples were collected monthly over 1 year in the Min River, eastern Tibetan Plateau, and analyzed for trace element composition. The dissolved trace elements exhibited different relationships with increasing discharge compared with major elements. The elements analyzed can be divided into three groups according to their behavior in response to changing discharge: (1) elements that showed weak positive correlation with discharge, e.g. Cu, V, and Ba; (2) elements that exhibited weak negative correlation with discharge, including Rb, Sr, Pb, Sb, Zn, Cr, Cd, and U; and (3) elements that displayed no significant correlation with variation in discharge, e.g. Ti, Fe, Co, Ni, and As. Cu was strongly affected by anthropogenic activities and flushed into the river with increasing discharge. Ba has a strong solubility in the terrestrial environment, dissolved quickly, and was released into the river. The positive relationship between V concentration and discharge may be attributed to secondary reactions, such as precipitation and adsorption on oxides and aluminosilicate clays. Conservative behavior had an impact on the geochemical behavior of Sr and Rb across hydrologic variation. Pb, Zn, Sb, Cd, and Cr underwent a mild dilution effect connected with anthropogenic activities. The chemostatic behavior of U was regulated by carbonate dissolution and biological uptake. In addition, higher temperatures enhanced biotic activities, affecting the concentrations of Fe and Ni. The relationship between power law slopes and coefficient of variation for discharge and solute concentration suggests that concentrations of trace elements vary significantly with increasing discharge compared with major elements. Silicate mineral weathering had less effect on the fluvial solutes with increasing discharge. Mining activity may exert an additional control on concentration-discharge dynamics of anthropogenic trace elements. [ABSTRACT FROM AUTHOR]

• Soil nitrogen content and isotope values changed after cropland abandonment. • Mineralization is more active in karstic topsoil than in the deep soil layer. • The loss NO 3 – mainly originated from the cropland topsoil in present karst areas. • Land use change from cropland to forest can reduce soil N loss to aquatic system. A large amount of cropland in the Southwestern (SW) China karst area has been abandoned since the implementation of the Grain for Green project at the end of the last century, which significantly impacted the biogeochemistry cycle in soil. However, the effect of cropland abandonment on the soil nitrogen (N) cycle and the N loss process is still little understood. N content and isotope analysis were used to assess karst soil's N fate and explore the N loss process in SW China. Soil samples were collected from four land uses, cropland (CR), abandoned CR (AC), shrubland and grassland (SG), and secondary forest (SF), by seasonal in a typically mixed land-use karst catchment at six soil depths. The results showed that the average soil particulate organic N (PON) content increased from 1.58 ± 0.49 g kg−1 to 2.70 ± 1.82 g kg−1, whereas average dissolved nitrate (NO 3 –-N) content decreased from 10.77 ± 8.87 mg kg−1 to 1.72 ± 1.84 mg kg−1 during revegetation. There was a decreasing amount of PON and dissolved N (NH 4 +-N、NO 3 –-N、TDN) content from surface to the bottom of the soil profile and large variation mainly occurred in 0 – 30 cm in the soil profiles of four different land uses, which suggests N transformation mainly occurred in topsoil (<30 cm). Mineralization was the major nitrogen transformation process that affected PON content and δ15N-PON values. The highest δ15N-PON fractionation (-5.0‰) in the soil profiles of the four types of land use caused by mineralization was detected in SF. Variation of N content and isotope values in soil profiles after cropland abandonment suggested that the loss of NO 3 –-N in karst catchment mainly came from the topsoil of cropland. Overall, N loss from the topsoil of cropland should pay more attention, while cropland abandonment can effectively reduce the loss of dissolved N from the thin karst soil layer. [ABSTRACT FROM AUTHOR]

Without careful land management, agricultural land in karst systems can pollute water courses, with polluted waters travel quickly to and through the sub-surface in karst systems. However, detailed understanding of how rapidly nitrate moves within the karst critical zone (from soils to aquifers) is limited by low resolution sampling for this highly-transmissive system. To understand nitrate behavior and its controlling factors, we deployed sensor technology at five sites to generate autonomously high-resolution time series of discharge and [NO3−N] in a farmed karst catchment in SW China. The [NO3−N] time series exhibited rapid response to rainfall-induced increases in discharge and a large magnitude in [NO3−N], ranging from 0.72 to 16.3 mg/L. The highest mean [NO3−N] and normalized annual fluvial export were observed in one headwater catchment with well-developed conduit structure. Elsewhere this was less-pronounced due to buffering by the karstic aquifer network as the contributing catchment area increased with distance downstream. Clear seasonal variation in NO3−N export occurred in response to source availability, most notable in catchments with valley agriculture: up to 97% of nitrate was exported from the headwater catchment in the wet season, with much of that loss occurring in only a couple of months, compared to 61% of nitrate exported at the larger catchment scale. The sensor time series showed that the aquifers were chronically polluted with nitrate. [ABSTRACT FROM AUTHOR]

China is experiencing rapid urbanization that has changed the water quality of rivers, especially nutrient loads. In this study, a typical urban river located in a karst area, Chengguan River, was chosen to explore the influence of urbanization on river ecosystems based on nutrient concentration and nitrate isotopes. The results show monthly variability of water chemistry and nutrient concentration. Nutrient concentration in two tributaries and the mainstem showed significant spatial variability, with heavy N and P pollution in one tributary near a suburban area, indicating a response to different levels of urbanization. Measurements of nitrate dual isotopes suggest that volatilization, assimilation, nitrification, and denitrification all occur in the polluted river. Water chemistry and nitrate isotopes show that major nitrogen sources included domestic waste and agricultural input, such as chemical fertilizer and manure. The results suggest that urbanization increases nutrient concentrations and accelerates the riverine nitrogen dynamic, and point to the need to manage point sources of sewage effluents to improve the water quality of urban rivers in southwestern China. [ABSTRACT FROM AUTHOR]

• Carbonate weathering dominates the water chemistry of river water which accounts for about 80.5 % of solutes. • The sensitivity of chemical weathering to climate change and topographic factors were found. • Forward model is combined with the mass balance to calculate the weathering rates. • Weathering rate is 6.0 t km−2 a−1 for silicate and 70.1 t km−2 a−1 for carbonate. Chemical weathering acts as a linkage between the solid earth and atmospheric CO 2 and thus affects the global climate throughout the geologic time. However, these processes have not been well-documented in the Himalayan Rivers due to the lack of information on the sources of solutes and pyrite oxidation. Here we present chemical compositions of surface water in the upper Indus River basin (UIRB), Western Himalayas, aiming to explore the sources of major ions, chemical weathering rates, associated CO 2 consumption rates, and their controlling factors. The total cation charge (1611 µEq) and average total dissolved solids (133 mg/L) of the UIRB waters were higher than those of the world's major rivers. HCO 3 − and Ca2+ dominated the ionic compositions of river water. The total major ions of analyzed rivers were mainly sourced from reservoirs including carbonates, evaporites, silicates, and atmospheric inputs. Quantitative investigation of solute sources indicated that carbonate weathering dominates the dissolved loads in river water, which accounts for approximately 80.5 %. The chemical weathering rates of silicate and carbonate were estimated to be 6.0 and 70.1 t km−2 a−1, with atmospheric CO 2 consumption rates of 91 × 103 and 503 × 103 mol km−2 a−1, respectively. The highest carbonate weathering rate (128.2 t km−2 a−1) in the UIRB was observed in the Suru River basin, which has the steepest catchment average slope. After considering pyrite oxidation, the actual CO 2 consumption rates by the silicates and carbonate in the basin were only approximately 80 % of the amount estimated under the presumption that carbonic acid donates all protons included in the chemical weathering. This study highlights the importance of pyrite oxidation for riverine carbon budget in the mountain rivers, Western Himalayas. [ABSTRACT FROM AUTHOR]

Correction to: I Scientific Reports i https://doi.org/10.1038/s41598-023-31831-1, published online 20 March 2023 The original version of this Article contained errors in the Results and discussion, under the subheading "Mechanisms for Fe-DOMP formation and isolation", "2 I FeCl i SB 3 sb + 6 I NaOH i + 6 I DOM i - I COOH i = 2 I Fe i SP 3 sp + 6 I DOM i - I COO i SP - sp + 2 I NaCl i SB 3 sb + 6 I H i SB 2 sb I O i ." now reads: "2 I FeCl i SB 3 sb + 6 I NaOH i + 6 I DOM i - I COOH i = 2 I Fe i SP 3 sp + 6 I DOM i - I COO i SP - sp + 6 I NaCl i + 6 I H i SB 2 sb I O i ." The original article can be found online at https://doi.org/10.1038/s41598-023-31831-1. [Extracted from the article]

• Monte Carlo inversion model is employed to constrain sources of riverine solutes and pyrite-derived δ34S. • Contribution of sulfide oxidation and δ34S value of sulfide minerals jointly control the riverine δ34S SO4. • ΔALK/ΔDIC ratio can be used to reflect the effect of chemical weathering on atmospheric p CO 2. • Sulfuric acid weathering in karst-dominated landscape serves as a carbon source at long timescale. Sulfide oxidation, coupled with carbonate weathering is thought to be a source of CO 2 over geological timescales to offset CO 2 drawdown from silicate weathering. Its impact on the carbon budget of weathering at the catchment scale is generally constrained by utilizing riverine water chemistry and the isotope value (δ34S) of sulfate. However, the multiple origins of riverine sulfate and the high variability of sulfide-derived δ34S certainly limit the determination of sulfate sources and thus our understanding of the role of sulfuric acid-induced weathering in the carbon budget. In this study, to quantify the carbon budget between weathering by carbonic and sulfuric acids in mountainous catchments (the Yinjiang River, the Shiqian River, and the Yuqing River) in southwest China, a Monte Carlo inversion model is employed for major element concentrations and sulfate δ34S (δ34S SO4). This inversion quantitatively partitions the cations and sulfate between different sources, and further identifies the pyrite-derived δ34S and the flux ratios of alkalinity to dissolved inorganic carbon (ΔALK/ΔDIC). Inversion results reveal that the majority of major cations (>90 %) is derived from carbonate (calcite and dolomite) dissolution, and that riverine sulfate budget is predominately contributed by pyrite oxidation and precipitation. In the Yinjiang River, the average δ34S SO4 is 8.4 ‰ in the upper and middle reaches, but declines significantly to 0.4 ‰ in the lower reaches. In the Shiqian River and Yuqing River, δ34S SO4 mainly cluster around 3.6–5.7 ‰ and 5.5–8.5 ‰, respectively. Inversion results suggest that the primary controls on δ34S SO4 are the variability of lithology and the variation in the proportional contribution of pyrite oxidation to riverine sulfate. In the Yinjiang River, the fraction of H 2 SO 4 -driven weathering is highly variable, and higher in the lower reaches than in the upper reaches, attributing to distinct underlying lithology in the catchment (a widespread distribution of coal-bearing strata). The weathering fluxes with 1 < ΔALK/ΔDIC < 2 evidenced that the negative alkalinity flux from carbonate weathering driven by sulfuric acid from both pyrite oxidation and acid deposition counteracts much of the alkalinity flux from silicate weathering. This is implicated on the timescale between marine carbonate precipitation and sulfate reduction (>5–10 kyr and <10 Myr), indicating that weathering in these catchments acts as short-term sinks of atmospheric CO 2 but long-term sources of it. Moreover, reanalysis of prior datasets of karst-dominated catchments in China also highlight the important role of pyrite oxidation and acid precipitation in the carbon budget. [ABSTRACT FROM AUTHOR]

• The source-transformation-pathway of nitrate is identified in a karst river. • Most nitrate is transported through subsurface rather than groundwater pathway. • Sustained leaching loss of nitrogen from karst matrix occurred throughout the year. • Non-point source and nitrification-derived nitrate should be given specially attention. A comprehensive understanding of nitrate dynamics in rivers is vital for nitrogen management, especially for the karst zone with high leaching of nitrate producing potential risk to environmental quality. However, identification of the source-transformation-pathway of nitrate is limited in the karst rivers. Thus, a suit of hydrogeochemical parameters, including δ15N-NO 3 −, δ18O-NO 3 −, δ13C-DIC, δ18O-H 2 O, soil-related parameters (DOC) and geogenic ions (Mg2+, DIC), were used to identify nitrate sources and dynamics in the Wujiang River, a typical karstic river as a tributary of Changjiang River. The combined use of a conceptual model of normalized NO 3 − and DOC, and other hydrogeochemical parameters (δ13C-DIC, Mg2+, DIC) suggested that most nitrates were transported through the soil/epikarst pathway in the wet season, whereas >70 % of nitrates were transported through groundwater pathway in the dry season for Wujiang River. Nitrification and mixing were the dominant processes, meanwhile ∼31 % of nitrate was denitrified in the wet season in this study. The reanalysis of δ15N-NO 3 − and δ18O-NO 3 − values for reported karstic rivers in China and worldwide also revealed the predominant nitrification and denitrification in karst regions. The Bayesian model indicated that chemical fertilizer (CF, 42 %) and soil organic nitrogen (SON, 32 %) contributed the most in the wet season, while ∼60 % of nitrate originated from SON (31 %) and manure and sewage wastes (M&S, 30 %) in the dry season in the Wujiang River. The sustained contribution of non-point sources from nitrification through the soil/epikarst pathway might be related to the widespread porosities in the karst rivers. Thus, measures to reduce nitrogen leaching and improve fertilizer use efficiency should be considered, like water and soil conservation, slow-release fertilizer and nitrification inhibitors. Additionally, a suit of hydrogeochemical indicators proves to be helpful for identification of source, transformation and transport pathway of nitrate in the karst basin. [ABSTRACT FROM AUTHOR]

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/km 2 /yr for the main stream of the Liao River and 7.01, 25.0 and 2.80 t/km 2 /yr for the Daliao River, respectively. The associated CO 2 consumption rates by silicate weathering and carbonate (+gypsum) weathering are 10.1 and 9.94 × 10 3 mol/km 2 /yr in the main stream of the Liao River and 69.0 and 80.4 × 10 3 mol/km 2 /yr in the Hun-Tai River, respectively. The Daling River basin has the highest silicate weathering rate (TDS sil , 3.84 t/km 2 /yr), and the Hun-Tai River has the highest carbonate weathering rate (TDS carb , 25.0 t/km 2 /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. [ABSTRACT FROM AUTHOR]

Surface waters impacted by urbanization and anthropogenic activities, especially streams and rivers, can be a significant source of nitrous oxide (N 2 O), but little is known about how the nitrogen enrichment in urban and rural rivers will increase the N 2 O emission. Tianjin surface waters including urban and rural river network and lakes were sampled and analyzed for N loadings and N 2 O concentrations. The study showed that eutrophied urban rivers in Tianjin were oversaturated with respect to N 2 O with a saturation ranging from 252% to 3116% and acted as source of N 2 O whereas rural rivers were generally undersaturated, with the a saturation ranging from 3% to 354% and acted as a sink of N 2 O. Mean values of estimated N 2 O fluxes in urban and rural rivers were 2.10 μmol m − 2 d − 1 and − 0.24 μmol m − 2 d − 1 , respectively. Anthropogenic inorganic N load plays primary control on the distribution of N 2 O saturation in heavily eutrophied rivers and estuaries, but N 2 O emission did not increase as much as expected in response to high N inputs, especially in rural rivers. Whereas nitrification might be the main process responsible for N 2 O production in urban lakes and rivers in Tianjin, both nitrification and denitrification could contribute to N 2 O production in nearby estuaries. In comparison, denitrification is a N 2 O sink in rural rivers of Tianjin. The annual emission from the river network of Tianjin was estimated to be 5.78 × 10 3 kg N-N 2 O, a moderate emission when compared with worldwide rivers, but N 2 O emission in urban rivers and lakes indicated that globally aquatic N 2 O emission rate and fluxes were probably underestimated in the 2007 IPCC report. More efforts should be paid to globally quantified N 2 O in eutrophied urban rivers for better assessment of N 2 O emission in riverine systems. [ABSTRACT FROM AUTHOR]

Special hydrological structures coupled with rainfall and agricultural activities have great impacts on water quality in karst areas. High-frequency hydro-chemical, dual nitrate isotopes and a Bayesian mixing model (SIAR) were employed to investigate the effect of heavy rainfall events on nitrogen patterns in surface and underground streams and explore the implications for nitrogen pollution prevention in a typical karst agricultural catchment in Southwest China. The results showed that [NO 3 --N] was relatively high in both surface and underground streams and the average value in surface stream was two times higher than in underground stream. The lowest [NO 3 --N] of underground stream was found in the falling limb of the hydrograph. According to source apportionment by SIAR, chemical fertilizer was the dominant nitrate source in the study area, which contributed 52–81% and 29–78% of nitrate in surface stream and underground stream, respectively. The highest dissolved inorganic nitrogen flux and [NO 3 --N] in surface stream was 5.7 times and 2.4 times higher, respectively, than in underground stream over the same period, which suggested that surface runoff rather than underground stream was the main route of rapid nitrogen loss in the karst catchment during heavy rainfall events. Reasonably planning the fertilization time and optimizing nitrogen fertilizer use should be considered to decrease nitrogen loss from farmland. Rational use of a widespread karst underground conduit system to reduce water nitrogen content may also be a potential method for achieving nitrogen removal. • Nitrogen patterns in agricultural surface and underground streams were investigated. • Nitrate in surface and ground flows mainly origin from chemical fertilizer. • Karst surface runoff was the main route of rapid nitrate loss during rainfall events. • Karst agricultural water management should consider the structure characteristics. [ABSTRACT FROM AUTHOR]

Lithium (Li) concentrations and Li isotopic compositions of the main channel of the Changjiang River and its main tributaries were measured to better understand the geochemical behavior of Li and its isotopic fractionation during weathering and erosion. The Li concentrations of the dissolved loads of the main channel range from 475 to 4570 nmol/l and decrease from the upper reaches to the lower reaches; values are clearly higher than those reported for many of the world’s largest rivers. Samples with very high Li concentrations are affected by the dissolution of evaporites in the headwater region. The δ 7 Li values of the particulate material has a narrow range (−4.7‰ to +0.7‰), whereas the dissolved load has very variable δ 7 Li (+7.6‰ to +42.1‰), with values increasing from the upper reaches to the lower reaches. After correction for contributions other than silicate weathering, we show that the Li isotopic compositions of the dissolved load reflect the balance between dissolution of primary minerals and preferential incorporation of the light isotope into secondary products of erosion which enrich the solution in 7 Li. The evolution of the isotopic composition from the Upper Reaches to the Lower Reaches is mainly controlled by the fraction of Li incorporated/adsorbed in/onto secondary minerals, and in fine by probably the difference in weathering regimes (i.e. kinetic limited vs transport limited). We also show that the magnitude of the apparent isotopic fractionation between the bedrock and dissolved Li for example are not always only due to variation of the isotopic fractionation factor but might also be due to composition (Li content of the bedrock) and mineralogical controls. The composition of the eroded silicate crust estimated by a steady state mass balance reveals the important contribution of sedimentary rocks (shales) and highlights the effects of sedimentary recycling on the composition of the continental crust. [ABSTRACT FROM AUTHOR]

Appropriate characterisation of isotope signatures (δ18O and δD) of groundwater, glaciers, and surface water in the Himalayan catchment are important for refining the sources of moisture and developing a modern isotope–elevation relationship for paleoelevation reconstructions. The Indus River located in Western Himalaya is previously unexplored in respect of the variation in water isotopic composition with elevation. In this study, water samples (n = 96) were collected from mainstream, tributaries, streams, glaciers, groundwater, lakes, hot springs, and pond water during the summer season. Results showed that δ18O signatures of the mainstream, tributaries and groundwater range from −15.1‰ to −12.3‰, −16.5‰ to −12‰, −13.8‰ to −12‰, with a mean value of −13.6‰, −14.7‰, −12.8‰, respectively. There was a northward rise in δ18O by 1.30‰ per degree of latitude in the tributary waters. The d -excess and δ18O values suggested that the key source of moisture in the studied river basin was mainly from westerlies and southwest monsoons. Thus, regional moisture recycling and subcloud evaporation contributed little in supplying moisture to the precipitation. The isotopic signature (δ18O) of the tributary stream and its surrounding regions conformed to a best-fit second-order polynomial relationship between δ18O and elevation over 3500 masl. Moreover, an δ18O elevation slope of −2‰/km is also established in this study area. This isotope–elevation relationship will be highly useful and can be applied to the Indus River and other Himalayan rivers for paleoelevation reconstruction. • Stable isotopes of surface water and groundwater in the UIRB are analyzed. • Surface waters showed variable isotopic spatial pattern in the upper Indus River. • Moisture sources in the UIRB mainly from southwest monsoons and westerlies. • Isotope-elevation link explored in the UIRB for paleo-elevation reconstruction. [ABSTRACT FROM AUTHOR]

Abstract: 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 , accounting for 46% and 74% of major cations and anions, respectively. The average total dissolved solids (TDS, 116mgL−1) and total cation concentration (TZ+, 1388μEqL−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 0.40tkm−2 a−1, respectively. The total rock weathering rate for the whole Songhuajiang Basin is approximately 7.78tkm−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 molkm−2 a−1 and 66.6×103 molkm−2 a−1 by carbonate and silicate weathering, respectively. As a sub-basin, the 2nd Songhuajiang has the highest (18.9tkm−2 a−1) while the Nenjiang River Basin has the lowest total rock weathering rate (5.03tkm−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 molkm−2 a−1) and is not much lower than that of Changjiang (112×103 molkm−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. [Copyright &y& Elsevier]

Abstract: Rapidly increasing populations, and associated intensification of agriculture, urbanization and industrialization, place increased demands on water resources and increased likelihood of pollution in many areas of the world. The Shuicheng Basin, southwestern China, is one such area and in order to understand water–rock interactions (carbonate dissolution) and anthropogenic impacts on groundwater quality in this karstic landform-dominated area, chemical as well as C, Sr and S isotopic compositions of groundwater (spring and well) and surface water (river) were measured during and following rainy seasons. The concentrations of various ions in groundwater were characterized by the dominant cations (Ca2+, Mg2+) and anions (, ), which account for more than 80% of the total ion concentration. Strontium isotope ratios (87Sr/86Sr, 0.70760–0.70918, mean 0.70831) and δ 13CDIC (−14.2‰ to −8.4‰, mean −10.7‰) indicate that the weathering dissolution of limestone controls Ca2+ and . The decrease in δ 13CDIC values with increasing concentrations of anthropogenic species (Cl−, and Na+) shows that the C isotopic composition of DIC can be a useful tracer of contaminants. Chemical compositions, hydrogeological conditions and δ 34S analyses showed increasing concentration, resulting from domestic wastewater, fertilizer applications, atmospheric inputs through coal combustion, and oxidation of sulfide minerals, which typically are abundant in coal formations in the basin. Groundwater from the old downtown, industrial and agricultural areas exhibited high concentrations of Cl−, , and Na+, suggesting the groundwater is impacted by significant levels of contamination from human activities. [ABSTRACT FROM AUTHOR]

Abstract: The chemical compositions of the surface/ground water of Guiyang, the capital city of Guizhou Province, China are dominated by Ca2+, Mg2+, , which have been derived largely from chemical weathering of carbonate rocks (limestone and dolomite). The production of has multiple origins, mainly from dissolution of sulfate evaporites, oxidation of sulfide minerals and organic S in the strata, and anthropogenic sources. Most ground water is exposed to soil CO2 and, therefore, the H2CO3 which attacks minerals contains much soil C. In addition, the H2SO4 produced as a result of the oxidation of sulfides in S-rich coal seams and/or organic S, is believed to be associated with the chemical weathering of rocks. The major anthropogenic components in the surface and ground water include K+, Na+, Cl−, , with Cl− and being the main contributors to ground water pollution in Guiyang and its adjacent areas. The seasonal variations in concentrations of anthropogenic components demonstrate that the karst ground water system is liable to pollution by human activities. The higher content of in ground water compared to surface water during the summer and winter seasons, indicates that the karstic ground water system is not capable of denitrification and therefore does not easily recover once contaminated with nitrates. [Copyright &y& Elsevier]

• Large amounts of water and dissolved inorganic carbon were lost in the rivers of Hainan Island. • Significant evaporation and primary production co-existed in these tropical rivers. • Intensive in-stream hydrological and biogeochemical processes mainly occurred in headwater segments. Rivers play an important role in global water and carbon cycling, but there are still large uncertainties concerning evaporation and aquatic photosynthesis. Here we combined measurements of water chemistry, isotopic compositions (i.e., δ D w , δ 18 O w , δ 13 C DIC and ▵ 14 C DIC) and geographic characteristics (i.e., river width) to elucidate in-stream hydrological and biogeochemical processes across rivers in Hainan Island, China. The results showed that dissolved inorganic carbon (DIC) in river waters was largely of modern origin, with about 95% from contemporary biogenic sources based on an isotopic mass balance of ▵ 14 C DIC. Significant evaporation and aquatic primary production co-occurred in these tropical rivers with large amounts of water and DIC being rapidly turned over in the water column, altering the water cycle and the carbon balance. High rates of evaporation and aquatic primary production were observed in the headwater segments, with narrow river width but broad available reactive surface area at the air-water interface. The asymmetric aquatic photosynthesis at different river segments caused the spatial heterogeneities of dissolved solutes. The results suggest that the available reactive area at the water-air interface is responsible for synchronous water loss and dissolved carbon evolution in flat tropical rivers. This study provides evidence that intense evaporation and aquatic photosynthesis mainly occurred in headwater segments, which has implications for understanding global carbon cycling. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: This paper presents hydrogeochemical and S isotopic characteristics of karstic surface and ground water in the karstic aquifers of Zunyi city of Guizhou Province, SW China. The average δ34S value of SO4 is +2.2‰ (n =28) in ground waters and +7.0‰ (n =15) in surface waters in the low flow season, while in the high flow season it is +1.0‰ in ground waters and +2.8‰ in surface waters. Natural and anthropogenic sources of the dissolved can be discriminated by a combined approach using water chemistry and stable S isotope data. A pollutant source of SO4 is estimated to have very high TDS contents and a narrow range of δ34S values (0‰ to +5.0‰). The water with a distinctively high δ34S value of +30.5‰ originates from an evaporite (gypsum and anhydrite)-bearing aquifer, and the δ34S values lower than −10‰ suggest an origin by oxidation of sulfide minerals in coal seams with intermediate TDS contents. [Copyright &y& Elsevier]

• Sources of organic carbon constrained by δ13C and Δ14C in river-reservoir system. • The effects of reservoirs on the transformation of OC are quantified. • The biological carbon pump process is greatly accelerated by the reservoir. • A new conceptual model reveals the effect of the reservoir on carbon cycling. Reservoirs have been constructed as clean energy sources in recent decades with various environmental impacts. Karst rivers typically exhibit high dissolved inorganic carbon (DIC) concentrations, whether and how reservoirs affect carbon cycling, especially organic carbon (OC)-related biogeochemical processes in karst rivers, are unclear. To fill this knowledge gap, multiple tracer methods (including fluorescence excitation-emission matrix (EEM), ultraviolet (UV) absorption, and stable carbon (δ13C) and radiocarbon (Δ14C) isotopes) were utilized to track composition and property changes of both particulate OC (POC) and dissolved OC (DOC) along river-transition-reservoir transects in the Southwest China karst area. The changes in chemical properties indicated that from the river to the reservoir, terrestrial POC is largely replaced by phytoplankton-derived OC, while gradual coloured dissolved organic matter (CDOM) removal and addition of phytoplankton-derived OC to the DOC pool occurred as water flowed to the reservoir. Higher primary production in the transition area than that in the reservoir area was observed, which may be caused by nutrient released from suspended particles. Within the reservoir, the production surpassed degradation in the upper 5 m, resulting in a net DIC transformation into DOC and POC and terrestrial DOM degradation. The primary production was then gradually weakened and microbial degradation became more important down the profile. It is estimated that ~3.1–6.3 mg L −1 (~15.5–31.5 mg-C m −2 (~10–21%)) DIC was integrated into the OC pool through the biological carbon pump (BCP) process in the upper 5 m in the transition and reservoir areas. Our results emphasize the reservoir impact on riverine OC transport, and due to their characteristics, karst areas exhibit a higher BCP potential which is sensitive to human activities (more nutrient are provided) than non-karst areas. [Display omitted] [ABSTRACT FROM AUTHOR]

The production of fluorescent dissolved organic matter (FDOM) by phytoplankton and its subsequent degradation, both of which occur constantly under diurnal-day time sunlight and by night time dark-microbial respiration processes in the upper layer of surface waters, influence markedly several biogeochemical processes and functions in aquatic environments and can be feasibly related to global warming (GW). In this work sunlight-mediated high-temperature was shown to accelerate the production of FDOM, but also its complete disappearance over a 24-h diurnal period in July at the highest air and water temperatures (respectively, 41.1 and 33.5 °C), differently from lower temperature months. Extracellular polymeric substances (EPS), an early-state DOM, were produced by phytoplankton in July in the early morning (6:00–9:00), then they were degraded into four FDOM components over midday (10:00–15:00), which was followed by simultaneous production and almost complete degradation of FDOM with reformation of EPS during the night (2:00–6:00). Such transformations occurred simultaneously with the fluctuating production of nutrients, dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and the two isotopes (δ15N and δ18O) of NO 3 −. It was estimated that complete degradation of FDOM in July was associated with mineralization of approximately 15% of the initial DOC, which showed a nighttime minimum (00:00) in comparison to a maximum at 13:00. FDOM identified by excitation-emission matrix spectroscopy combined with parallel factor analysis consisted of EPS, autochthonous humic-like substances (AHLS) of C- and M-types, a combined form of C- and M-types of AHLS, protein-like substances (PLS), newly-released PLS, tryptophan-like substances, tyrosine-like substances (TYLS), a combined form of TYLS and phenylalanine-like substances (PALS), and their degradation products. Finally, stepwise degradation and production processes are synthesized in a pathway for FDOM components production and their subsequent transformation under different diurnal temperature conditions, which provided a broader paradigm for future impacts on GW-mediated DOM dynamics in lake water. Unlabelled Image • EPS are produced from phytoplankton by light-induced high-temperature processes in the morning. • Disintegration of EPS into four FDOM and their complete disappearance occur in 24-h. • EPS follows humic-like and protein-like formation paths, until its mineralization. • Transformations of FDOM are related to changes of nutrients, DOC, DON and δ15N plus δ18O of NO 3 −. • Rapid mineralization of FDOM is a useful sign to predict the potential impact of GW. [ABSTRACT FROM AUTHOR]

• A novel fluorescent probe L for the detection of Zn2+ and Cu2+ was synthesized. • The detection of Zn2+ and Cu2+ was based on two different mechanisms. • Good selectivity of L towards Zn2+ and Cu2+ were observed. In this study, a novel fluorescent probe sensor, 7,8-benzochromone-3-carbaldehyde (fluorescein)hydrazone L , was designed and synthesized. Based on the photoinduced electron transfer (PET) process, L can detect Zn2+ in the solution of EtOH/H 2 O (9/1, V/V). The probe had high selectivity and sensitivity to Zn2+ with a lower detection limit of 3.4 × 10−7 M. Furthermore, the coordination ratio of L -Zn2+ was 1:1, which could be corroborated by Job's plot. In addition, in the EtOH/ H 2 O (5/2, V/V) solution of the probe L , Cu2+ was added to produce a marked change in color from achromatous to yellow, indicating that the probe L could detect Cu2+ by colorimetry, which was detectable by the naked eye, simply and quickly. According to the Benesi-Hildebrand equation, the complexing constants values of L -Zn2+ and L -Cu2+ were 9.8 × 104 M-1 and 1.009 × 105 M-1, respectively. [ABSTRACT FROM AUTHOR]

• Biological carbon influxes control the temporal dissolved inorganic carbon dynamics. • Dissolved organic carbon concentrations are highly affected by flushing effect. • Dissolved inorganic carbon dynamics in the Tibetan Plateau rivers play an important role in global carbon cycles. • Carbon concentrations and fluxes of the Tibetan Plateau rivers show high sensitivity to future global climate changes. Studying the temporal dynamics and fluxes of riverine dissolved carbon is crucial in understanding the regional and global carbon cycles under various climatic conditions. Here, we studied the behaviors and fluxes of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) responding to various hydrologic conditions in the Min River, originated from Tibetan Plateau. The DIC concentrations decreased with increasing runoff, partially reflecting dilution effect, which may be ascribed to the shortened fluid transit time and then the reduced contact time with rocks. Nevertheless, DOC concentrations were positively correlated with runoff, which can be attributed to that a large amount of soil organic carbon flowed into the river as a result of the strong flushing effect. The negative relationship between δ13C DIC and runoff could be explained by soil CO 2 influx and organic matter degradation during the high flow season. ΔDIC (the production of DIC with changing hydrologic conditions) had a strong positive correlation with water temperature due to the accelerated DIC production rates by high temperature, which always co-varied with intense precipitation in Asian monsoonal regions. The mean DIC/DOC ratio in the Min River was 15.09, and the DOC and DIC fluxes were 1.1 and 15.2 t C km−2 yr−1, respectively, for the studied year. And the DOC and DIC fluxes varied dramatically with runoff changes, suggesting that hydrologic conditions were critical factors for the variations in dissolved carbon export. This study shows that carbon dynamics of rivers draining from the Tibetan Plateau are greatly affected by short-term climatic variabilities, which has implications for understanding global carbon cycle under future climate change. [ABSTRACT FROM AUTHOR]

Lignin is the second most abundant natural biopolymer, which is a potential alternative to conventional fossil fuels. It is also a promising material for the recovery of valuable chemicals such as aromatic compounds as well as an important biomarker for terrestrial organic matter. Lignin is currently produced in large quantities as a by-product of chemical pulping and cellulosic ethanol processes. Consequently, analytical methods are required to assess the content of valuable chemicals contained in these complex lignin wastes. This review is devoted to the application of mass spectrometry, including data analysis strategies, for the elemental and structural elucidation of lignin products. We describe and critically evaluate how these methods have contributed to progress and trends in the utilization of lignin in chemical synthesis, materials, energy, and geochemistry. [ABSTRACT FROM AUTHOR]

• DIC and δ13C DIC showed strong spatiotemporal heterogeneities in karst river-reservoir system. • After damming, water chemical characteristics varied markedly in reservoir profiles. • The reservoir effect index (R i) can be used to reveal relevant biogeochemical processes. • Reservoir regulation can be optimized to reduce the damming effect based on R i. Cascade damming has seriously affected the hydrologic regimes and solutes transport of the river systems. However, the effect of damming on carbon cycle and the underlying mechanisms are still unclear. In this study, to reveal the effects of damming on riverine dissolved inorganic carbon (DIC) transport, the water chemistry and stable isotopic signature of dissolved inorganic carbon (δ13C DIC) were analyzed in the tributaries and four subtropical karst reservoirs on the Pearl River in southern China. From reservoir epilimnion to hypolimnion, DIC concentrations increased from 183.2 to 229.4 mg L−1, 167.6 to 192.0 mg L−1, 179.1 to 181.5 mg L−1, and 182.4 to 183.8 mg L−1 while δ13C DIC decreased from −6.6‰ to −9.7‰, −7.8‰ to −10.4‰, −9.7‰ to −10.0‰ and −9.9‰ to −10.0‰ in the Chaishitan (CST), Longtan (LT), Yantan (YT), and Dahua (DH) reservoirs, respectively. Our analyses suggest that primary production and organic matter degradation were two dominant processes in carbon evolution in the epilimnion and hypolimnion, respectively. However, there was no obvious spatial heterogeneity of solutes' concentration in the DH reservoir. Our results also suggested that cascade reservoirs had a regional damming effect and could be significantly weakened without damming or in daily regulated reservoirs. Furthermore, δ13C DIC had a significant positive relationship with the reservoir effect index (R i), which was affected by hydraulic retention time and water temperature in the water column of reservoirs and is useful to evaluate the thermal stratification strength. This study highlights that dam constructions affected carbon transport and transformation significantly, and the degree of the damming effect on the carbon cycle can be expressed by R i. [ABSTRACT FROM AUTHOR]