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Purpose: This study aimed to explore how well persons with anomic aphasia communicate information during discourse regarding quantity, quality, and efficiency compared to neurotypical controls, to investigate the influence of discourse tasks on informativeness and efficiency and to examine impact factors like aphasia severity and cognitive ability. Method: Language samples of four discourse tasks from 31 persons with anomic aphasia and 31 neurotypical controls were collected from Mandarin AphasiaBank. Correct information unit (CIU) analysis measures including the total number of CIUs, percentage of CIUs, CIUs per minute, and words per minute were calculated. Group differences and the effects of discourse tasks on informativeness and efficiency were investigated. Correlations of CIU analysis measures with aphasia severity and cognitive ability were examined. Results: Persons with anomic aphasia showed lower efficiency in conveying information than controls. They underperformed controls on all CIU analysis measures when executing story narrative tasks. Discourse tasks influenced the informativeness and efficiency of both groups. Neurotypical controls delivered the greatest quantity of information most efficiently when narrating stories. Persons with anomic aphasia exhibited reduced quantity of information during procedural discourse and displayed superior information quality in sequential-picture descriptions. Discourse information may be impacted by aphasia severity and cognitive ability, with varying effects depending on the task. Conclusions: Persons with anomic aphasia are inefficient in communicating discourse messages and perform poorly on all measures in story narratives. When measuring discourse information, the effects of discourse tasks and factors like aphasia severity and cognitive ability should be considered. [ABSTRACT FROM AUTHOR]

To assess how chemical weathering processes in large high-relief river systems respond to climatic variability, we studied seasonal changes in radiogenic strontium (87Sr/86Sr) and stable calcium (δ44/40Ca) and magnesium (δ26Mg) isotopes in the Jinsha and Yalong rivers, which drain the southeastern Tibetan Plateau. During the low-runoff season, with discharge (Q) < 2000 m3/s, the river waters reflect the Sr, Ca, and Mg isotope signatures of recharge meltwaters, with additional isotope fractionation signals for Ca and Mg related to secondary mineral precipitation, which might imply that meltwater flushes soil solutions from the soil. During medium-runoff intervals (2000 m3/s < Q < 4000 m3/s), the Sr, Ca, and Mg isotope signatures in the Jinsha river waters are similar to those of the headwaters, which are influenced by evaporite dissolution, while the Yalong is affected by greater carbonate weathering relative to silicate weathering. In both rivers, bedrock dissolution governs the chemical composition of the river waters. During the high-runoff season (Q > 4000 m3/s), storms generate rapid overland flow, which transfers large volumes of soil into the rivers, such that soil weathering plays an important role in regulating riverine chemical compositions. At these times, the riverine Ca and Sr isotope evolution is influenced by secondary mineral dissolution and sediment–water cation exchange. Overall, this study highlights the potential of combining multiple isotope systems (Sr, Ca, Mg) to trace the dynamics of water–rock interaction under variable hydrological conditions. [ABSTRACT FROM AUTHOR]

Nitrogen dynamics at ecosystem levels profoundly impact the Earth's surface system due to their environmental and ecological significance. Exploring the sources and transformation of nitrogen in various Critical Zones is vital to understanding biogeochemical cycles and sustainable development. This study summarized nitrogen characteristics in soil profiles and nitrogen dynamics in diverse terrestrial ecosystems based on data from typical Critical Zones of China. The results indicated that nitrogen accumulates in the deep soils of cropland ecosystems due to intensive fertilizer applications, which potentially harms soil functions and water quality. Therefore, it is necessary and meaningful to take adequate measures to alleviate nitrogen accumulation in deep soils. Additionally, surplus nitrogen transported into groundwater and riverine systems from soil has emerged as an important issue for environmental management. There are serious nitrogen pollution issues in many river water and groundwater areas, which could be addressed by reducing the fast leaching and considerable nitrogen accumulation in the vadose zone. Systematic and long-term observational studies are needed to achieve the ultimate goal of ecological conservation and high-quality development. Therefore, future research should consider monitoring and evaluating ecosystems based on the long-term Critical Zone Observatories networks to advance appropriate environmental management strategies that adapt to nature's rules and strengthen the ecosystem service function for sustainable development. [ABSTRACT FROM AUTHOR]

• Carbon transport and transformation varies in two reservoirs with different geological settings. • Karst reservoirs exhibit a higher Revelle factor (RF) and low CO 2 emissions. • Attention should be paid to the high CO 2 emission effect of non-karst reservoirs. • Consider geological settings when estimating the global budget for reservoir CO 2 emissions. Carbon migration, transformation, and emissions as CO 2 in reservoir and lake systems have been extensively studied. However, uncertainties persist regarding carbon cycling variations in both karst and non-karst regions within large thermal stratified river-reservoir systems. To address this knowledge gap, we combined measurements of water chemistry, isotopic compositions (δ13C), partial pressure of CO 2 (p CO 2), and CO 2 fluxes (F CO2) to elucidate the differences, control mechanisms, and environmental effects of various carbon biogeochemical processes in the Hongjiadu reservoir (HJD, karst reservoir) and Shangyoujiang reservoir (SYJ, non-karst reservoir), Yangtze River basin, China. Our results demonstrate that key biogeochemical processes are associated with CO 2 production and emissions. The stronger biological carbon pump (BCP) effect in the lentic area of the HJD reservoir limited CO 2 emission (0.9 ± 5.0 mmol m−2 d−1) compared to the SYJ reservoir (50.9 ± 33.4 mmol m−2 d−1), leading to low dissolved inorganic carbon (DIC) and high saturation state of carbonate minerals in the lentic epilimnion. Although the released water from both reservoirs acted as hotspots for CO 2 emissions, the results of higher Revelle factor (RF) in the HJD reservoir than SYJ reservoir suggest the greater buffer capacity and lower sensitivity of OC degradation changes in DIC. Despite the shorter hydraulic retention time (HRT) of SYJ reservoir (120 d) compared to HJD reservoir (368 d), F CO2 was 3.5 times higher than that of the HJD reservoir (652.9 mmol m−2 d−1). Moreover, upon analyzing selected reservoirs worldwide, it becomes apparent that karst reservoirs demonstrate a reduced potential for CO 2 emissions. Our results indicate that the impact of varying geologic settings should be considered to minimize errors in regional and global CO 2 emission estimates. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: This study was designed to examine the hypothesis that discourse task types influence language performance in Mandarin Chinese--speaking people and to reveal the discourse task-specific linguistic properties of persons with anomic aphasia compared to neurotypical controls. Method: Language samples from persons with aphasia (n = 31) and age- and education-matched controls (n = 31) across four discourse tasks (sequential-picture description, single-picture description, story narrative, and procedural discourse) were collected from Mandarin AphasiaBank. Task-specific distributions of parts of speech were analyzed using mosaic plots. The main effects of tasks in each group and the between-group differences within each task for several typical linguistic variables were evaluated, including the mean length of utterance, tokens, moving-average type-token ratio, words per minute, propositional density, noun--verb ratio, noun percentage, and verb percentage. Results: The results revealed an impact of discourse tasks on most language variables in both groups. In the healthy controls, story narratives yielded the highest total words and lowest verb percentage. In the aphasia group, procedural discourse elicited the fewest total words and densest expressions, whereas their single-picture descriptions had the highest noun--verb ratio. For all tasks, the aphasia group performed worse than the control group in the mean length of utterance, tokens, moving-average type-token ratio, and words per minute. For noun--verb ratio, noun percentage, and verb percentage, only one task (i.e., single-picture description) showed significant between-group differences. Conclusion: The selection of discourse tasks should be addressed in assessments and interventions for Mandarin Chinese--speaking individuals with aphasia to obtain more accurate and feasible outcomes. [ABSTRACT FROM AUTHOR]

The balance between alkalinity generation by carbonate and silicate weathering and sulfuric acid generation by sulfide weathering controls the effect of weathering on atmospheric p CO 2 over geologic timescales. How this balance varies across environmental gradients remains poorly constrained. Here, we analyze this balance across an erosional gradient of two orders of magnitude in the Three Rivers (Yangtze, Mekong, and Salween Rivers) Headwater Region (TRHR), eastern Qinghai-Tibet Plateau (QTP). By employing major element chemistry and multiple isotopes (δ34S SO 4 , δ18O SO 4 , and δ18O H 2 O) coupled with forward and inverse approaches, we unmix contributions of silicates, carbonates, evaporites, and sulfides to the total weathering budget. Across the TRHR, riverine SO 4 2– is derived mainly from a mixture of an evaporite source with uniform values of δ34S SO 4 and δ18O SO 4 , and a sulfide source that contributes highly variable values of δ34S (−12.2 ‰ to +4.1 ‰) and δ18O (−17.7 ‰ to −1.6 ‰). Contributions of sulfide oxidation to riverine SO 4 2– vary from 16 % to 94 %, and sulfuric acid consumes 6 % to 63 % of the alkalinity produced by weathering. The fractions of weathering alkalinity derived from carbonate weathering range from 36 % to 98 % relative to silicate weathering. The combination of silicate, carbonate, and sulfide weathering suggests that the instantaneous weathering fluxes of most sampled catchments in the TRHR act as a sink of atmospheric CO 2 over timescales shorter than marine carbonate burial (∼104 years), but as a carbon source over timescales longer than carbonate burial and shorter than sulfide burial (∼107 years). The spatial variability of the balance between alkalinity and acid generation, and, thus, the relationship between chemical weathering and atmospheric p CO 2 , are largely dependent on lithology. However, within comparable lithologic settings, sulfide and carbonate weathering rates rise with increasing erosion, whereas silicate weathering rates remain constant. Consequently, plateau weathering shifts from a sink to a source of atmospheric CO 2 with increasing erosion. These findings suggest that sulfide weathering is more sensitive to erosion than carbonate and silicate weathering, and that it could play an important role in the long-term carbon cycle during mountain building. [ABSTRACT FROM AUTHOR]

• Most rainfall events showed N-Q pattern as a figure-of-eight hysteresis. • Hydrological connectivity and source availability determined N-Q patterns. • Source availability determined nitrate loading of event flow in karst area. • Variation in event-driven N loading and concentration was explained well. • Nitrate level and hydro-chemistry are not well explained by flow characteristics. Karst terrain seasonal monsoonal rainfall is often associated with high concentrations of nitrate-N in streams draining agricultural land. Such high concentrations can pose problems for environmental and human health. However, the relationship between rainfall events that mobilize nitrate and resulting nitrate export remains poorly understood in karst terrain. To better understand the processes that drive nitrate dynamics during rainfall events, the characteristics of individual rainfall events were analyzed using sensor technology. Thirty-eight rainfall events were separated from the high-frequency dataset spanning 19 months at a karst spring site. The results revealed that nitrate-discharge (N-Q) hysteresis in 79% of rainfall events showed anticlockwise hysteresis loop patterns, indicating nitrate export from long distances within short event periods. Karstic hydrological connectivity and source availability were considered two major determining factors of N-Q hysteresis. Gradual increase in hydrological connectivity during intensive rainfall period accelerated nitrate transportation by karst aquifer systems. Four principal components (PCs, including antecedent conditions PC1&3 and rainfall characteristics PC2&4 explained 82% of the cumulative variance contribution to the rainfall events. Multiple linear regression of four PCs explained more than 50% of the variation of nitrate loading and amplitude during rainfall events, but poorly described nitrate concentrations and hydro-chemistry parameters, which may be influenced by other factors, e.g., nitrate transformation, fertilization time and water-rock interaction. Although variation of N concentration during event flow is evident, accounting for antecedent conditions and rainfall factors can help to predict rainfall event N loading during rainfall events. Pollution of the karstic catchment occurred by a flush of nitrate input following rainfall events; antecedent and rainfall conditions are therefore important factors to consider for the water quality management. Reducing source availability during the wet season may facilitate to reduction of nitrogen loading in similar karst areas. [Display omitted] [ABSTRACT FROM AUTHOR]

• First measurements of PIC radiocarbon age in a karst reservoir system. • Photosynthesis-induced PIC precipitation is a source of PIC sink in the lentic zones. • The dissolution of autochthonous PIC is responsible for the build-up of DIC in the hypolimnion. • Discharge of the DIC-rich hypolimnion water through the dam causes downstream CO 2 emission to the air. Damming alters the biogeochemical cycling of carbon along river systems. However, the effects of river damming on the fate and transport of particulate and dissolved inorganic carbon (PIC and DIC) remain unclear. Here, we use dual isotope (13C and 14C) compositions, water chemistry, and electron microscopy to unravel the processes controlling the in-reservoir cycling of inorganic carbon in a river-reservoir system of a karst region of southwest China. From the reservoir's fluvial to lentic zone, δ13C PIC decreases from −2.2 ‰ to −7.6 ‰, whereas the PIC radiocarbon age drops from 11,512 to 2,027 years B.P. Electron microscopy images and water chemistry provide further evidence of in-reservoir photosynthesis-induced carbonate precipitation of autochthonous PIC in the water column. Although part of PIC is dissolved into DIC in the reservoir's hypolimnion, the contribution of carbonate minerals (allochthonous PIC) accounted for 41 % of PIC based on an isotopic mass balance model. This indicates that the precipitation rate of autochthonous PIC was greater part of carbon cycle in the reservoir. Moreover, the autochthonous PIC accounted for 61 % of the PIC and its dissolution accounted for 50 % of the DIC and the high CO 2 efflux in the water discharging from the reservoir. The results shed light on the important role of autochthonous PIC in carbon cycling in karst river-reservoir systems. With continued dam construction in karst areas, the role of in-reservoir PIC production and dissolution on the riverine carbon cycle deserves more attention. [ABSTRACT FROM AUTHOR]

• Evaluating the carbon transformation intensity and amounts in the reservoir. • The ultimate reservoir impacts consume river carbon in most of the seasons. • Evaluating the influence of hydrological management and seasonal variation. • Providing the scientific basis for weakening the influence of reservoir impacts. Reservoirs are widely established worldwide with considerable environmental impacts, especially on the riverine carbon cycle. However, the influence of reservoirs on the cycling of different forms of carbon and its regulation factors (e.g., seasonal variations versus hydrological management) have not been simultaneously studied. To fill this knowledge gap, seasonal water samples from the deep subtropical reservoir (Longtan reservoir) in the Pearl River were collected, and the concentrations and stable carbon isotopes of dissolved inorganic carbon (DIC), dissolved organic carbon (DOC), and particulate organic carbon (POC) were determined. The variations in stable carbon isotopes of DIC (-11.4‰ to -5.2‰), DOC (-32.2‰ to -26.2‰), and POC (-38.9‰ to -25.3‰) in the river-reservoir system indicated active production and degradation processes in different layers. We estimated that up to 23.0% of DIC, 20.5% of DOC, and most POC were intercepted or degraded within the reservoir. Our results further illustrated that hydrological management (water storage regulation) and seasonal variations from different perspectives controlled the cycling of different forms of carbon in the reservoir. In addition, with the gradual increase in the number of reservoirs, hydrological management can be considered as a potentially effective strategy to adjust the carbon biogeochemical cycling of reservoirs in the future. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • There is an active SIC-CO 2 -SOC system and a fast C cycle in karst soils. • The impact of biological factors on SIC in karst soils exceeds expectations. • Both SOC and SIC are labile and susceptible to land use change in karst regions. • Ceasing tillage benefits SOC restoration which mainly occurs within topsoil. Soil is a key carbon reservoir balancing global carbon budget and regulating climate change. Barren soils in karst zones have weak capacity for soil and water conservation and are readily erodible, making the carbon biogeochemical processes within karst soils potentially rapid and complex. To explore the vertical variation of soil carbon under karst conditions and its response to land-use change, this study investigated concentrations and isotopic compositions of both soil organic and inorganic carbon (SOC and SIC) in different depths of four land-use types in a typical karst region, SW China. Results show that as soil depth increases, SOC concentrations decrease, and its δ13C ratios (from −27.3‰ to −19.4‰) increase in 0–20 cm depth but decrease at depths below 20 cm. The fresh SOC is mostly sequestered and cycled within the topsoil and subject to different controls than that of the subsoil. The turnover rate of SOC in karst soils does not directly co-vary with isotopic fractionation among different land uses. Long-term cultivation causes SOC loss from karst soils, which can be alleviated or even partially restored after farming cessation. By contrast, SIC represents < 10% of soil total carbon. The vertical heterogeneity of SIC variation and the direct influence of biological factors on SIC are both weaker relative to SOC. The low δ13C ratios of SIC (from −20.4‰ to −3.0‰) indicate there is intense dissolution and reprecipitation of pedogenic carbonate within karst soil, especially in the upper cultivated layers. These results highlight that both SOC and SIC are labile and susceptible to land-use change in karst zones, which need to be considered in estimating karst carbon sink and its role in balancing global carbon budget on variable temporal scales. [ABSTRACT FROM AUTHOR]

Carbon dioxide (CO 2) production and emissions from inland waters play considerable roles in global atmospheric CO 2 sources, while there are still uncertainties regarding notable nutrient inputs and anthropogenic activities. Urban inland waters, with frequently anthropogenic modifications and severely nitrogen loadings, were hotspots for CO 2 emissions. Here, we investigated the spatiotemporal patterns of partial pressure of CO 2 (p CO 2) and CO 2 fluxes (FCO 2) in typical urban inland waters in Tianjin, China. Our observation indicated that p CO 2 values were oversaturated in highly polluted waters, particularly in sewage rivers and urban rivers, exhibiting approximately 9 times higher than the atmosphere equilibrium concentration during sampling campaigns. Obviously, the spatiotemporal distributions of p CO 2 and FCO 2 emphasized that the water environmental conditions and anthropogenic activities jointly adjusted primary productivity and biological respiration of inland waters. Meanwhile, statistically positive correlations between p CO 2 /FCO 2 and NH 4 +-N/NO 3 −-N (p < 0.05) suggested that nitrogen biogeochemical processes, especially the nitrification, played a dominant role in CO 2 emissions attributing to the water acidification that stimulated CO 2 production and emissions. Except for slight CO 2 sinks in waters with low organic contents, the total CO 2 emissions from the urban surface waters of Tianjin were remarkable (286.8 Gg yr−1). The results emphasized that the reductions of nitrogen loadings, sewage draining waters, and agricultural pollution could alleviate CO 2 emissions from urban inland waters. [Display omitted] • CO 2 emissions from urban inland water contributed largely to atmospheric CO 2. • Land use affected the spatiotemporal variations of CO 2 emissions. • Nitrogen loading increases stimulated CO 2 production and emissions. • Acidification in the nitrification processes enhanced the CO 2 production and degassing. • Improving water quality could cut down CO 2 emissions from urban inland waters. [ABSTRACT FROM AUTHOR]

The teleconnection between the Asian monsoon system and North Atlantic forcing is an enduring prospect of the Earth's climate. During the Holocene interstadial, the Indian summer monsoon showed asynchronous weakening links to ice rafting events documented in the North Atlantic region. However, the sensitivity of the Indian Winter Monsoon in response to North Atlantic cold spells is unclear due to a lack of compelling evidence. This study aims to extract the deglacial Indian Winter Monsoon signals using lithogenic tracers in coastal sediments and explore its association with the North Atlantic cooling episodes. A 5.1 m sediment core was retrieved from Pottuvil Lagoon in the southeastern coast of Sri Lanka, and the concentrations of K, Rb, Mg, Al, and Ti in 101 sub-sections were analysed using ICP-MS. The core- chronology was established by Bacon 2.2 age-depth modelling based on calibrated AMS 14C dates. The monsoon signal was reconstructed using element proxies and compared with the drift ice indices from the North Atlantic deep-sea sediments. Results revealed distinct phases of intense monsoon activity at 2553–2984 years BP, 3899–5021 years BP, and 5244–5507 years BP intervals with intermittent weak phases during 2253–2553, 2984–3899, and 5021–5244 years BP. The episodes of the intensified Indian Winter Monsoon coincided with Bond Events 2, 3, and 4, showing a strong coherence with the North Atlantic's deglacial climate. Thus, on a millennial scale, North-Atlantic cooling has triggered intense winter monsoon conditions over the tropical Indian Ocean region from the mid to late Holocene. In comparison with regional monsoon archives, the Pottuvil winter monsoon record exhibits an anti-phase association with the Indian Summer Monsoon during Holocene ice-rafted debris events. The geochemical approach executed in this study could provide new insight into the millennial-scale pacing of the winter counterpart of the Indian monsoon links to climate extremes of high northern latitudes. [ABSTRACT FROM AUTHOR]

Soil gas diffusion significantly affects soil respiration and greenhouse gas emissions, and is strongly determined by soil structure (mainly pore structure) and water content. Given the challenge of quantifying soil gas diffusivity and pore structure, the effect of soil structure on gas diffusion under different moisture conditions remains elusive. Here we measured soil gas diffusivity ( D s / D 0 ) of intact and repacked soils under four typical land uses, including irrigated cropland (IC), native grassland (NG), native forest (NF), and wetland (WL), at different soil matric potentials (ψ , –1 ≤ ψ ≤ –1500 kPa) using one-chamber method. The pore structure of intact soils was quantified using micro-computed tomography (µ-CT) and soil water retention curve. The D s / D 0 for repacked soils with different bulk densities (1.2–1.5 g cm−3) and clay contents (14–35%) were further determined. Land use significantly affected D s / D 0 with NF > NG > IC > WL, and disturbing soils via repacking generally decreased D s / D 0 , especially for NF. Increased bulk density and clay content decreased D s / D 0 , particularly at low ψ (–50 ≤ ψ ≤ – 1500 kPa), under which D s / D 0 was controlled by volume of pores with diameter > 6 µm and particularly 6–300 µm. By contrast, D s / D 0 at relatively high ψ (–1 ≤ ψ ≤ –10 kPa) was driven by volume of pores with diameter > 300 µm. Furthermore, an empirical model of D s / D 0 was developed by incorporating a scale parameter, which quantifies the effects of soil pore structure on gas diffusivity. The developed model predicted the D s / D 0 under different land uses and moisture conditions better than most currently used models. Overall, this study reveals how soil structure quantitatively affected gas diffusivity under different land uses and moisture conditions, and provides a feasible model to predict soil gas diffusivity, which is critical for accurately estimating and predicting greenhouse gas emissions from soils. This study suggests the importance of considering soil structural parameters derived from soil water retention curve and/or µ-CT in predicting gas diffusion across different soil types and land uses. • Soil gas diffusivity ( D s / D 0 ) is greater in forest and grassland than crop and wetland. • Pores with size > 300 µm control D s / D 0 at matric potentials from –1 to –10 kPa. • Pores with size of 6–300 µm control D s / D 0 at matric potentials from –50 to –1500 kPa. • A soil gas diffusivity model incorporating soil pore structure was developed. [ABSTRACT FROM AUTHOR]

Investigating weathering processes in landslide-prone areas is important for understanding the carbon budget due to weathering during mountain building. Here, we present the monthly hydrochemistry and sulfur isotopic compositions of SO 4 2− (δ34S–SO 4 2−) in the Bailong River which drained landslide-prone areas in the northeastern Qinghai-Tibet Plateau. Ca2+ and HCO 3 − were dominant in cations and anions respectively, and δ34S–SO 4 2− values varied over a narrow range, from 5.1‰ to 6.7‰. We constrained the sources of major cations and SO 4 2− through an inverse model and the mass balance model of δ34S–SO 4 2−. The results showed that cations in the Bailong River were mainly from carbonate weathering, and sulfide oxidation was an important source of SO 4 2−. Weathering in the Bailong River catchment showed an CO 2 source over geologic timescales due to the reaction of H 2 SO 4. The relationship between weathering fluxes and physical erosion rate indicated that high runoff facilitated physical erosion, and in turn accelerated chemical weathering. However, under the conditions of extreme discharge and physical erosion, SO 4 2− fluxes from sulfide oxidation were not as high as expected, which was ascribed to the transport of old landslide deposits where most sulfides had been exhausted. Therefore, in tectonically active areas with massive landslides, the high erosion rate caused by landslides promoted chemical weathering, but sulfide oxidation did not respond sensitively to strong physical erosion under high runoff conditions. This study helped to understand the relationship among landslides, chemical weathering, and geologic carbon cycle. • Carbonate weathering is the main contributor to dissolved cations in the Bailong River. • Sulfide oxidation is the main source of SO 4 2− in the Bailong River. • High runoff facilitated physical erosion, and in turn accelerated chemical weathering. [ABSTRACT FROM AUTHOR]

Ferric ions can bind strongly with dissolved organic matter (DOM), including humic acids (HA), fulvic acids (FA), and protein-like substances, whereas isolation of Fe-DOM precipitates (Fe-DOMP) and their biochemical characteristics remain unclear. In this work FeCl3 was used to isolate DOM components from various sources, including river, lake, soil, cow dung, and standard tryptophan and tyrosine, through precipitation at pH 7.5–8.5. The Fe-DOMP contribute to total DOM by approximately 38.6–93.8% of FA, 76.2% of HA and 25.0–30.4% of tryptophan and tyrosine, whilst fluorescence spectra allowed to monitor/discriminate the various DOM fractions in the samples. The relative intensity of the main infrared peaks such as 3406‒3383 cm−1 (aromatic OH), 1689‒1635 cm−1 (‒COOH), 1523–1504 cm−1 (amide) and 1176–1033 cm−1 (‒S=O) show either to decline or disappear in Fe‒DOMP. These results suggest the occurrence of Fe bonds with various functional groups of DOM, indicating the formation of π–d electron bonding systems of different strengths in Fe‒DOMP. The novel method used for isolation of Fe-DOMP shows promising in opening a new frontier both at laboratory and industrial purposes. Furthermore, results obtained may provide a better understanding of metal–organic complexes involved in the regulation of the long-term stabilization/sequestration of DOM in soils and waters. [ABSTRACT FROM AUTHOR]

Doubly-substituted methane isotopologues (13CH3D and 12CH2D2) can provide unique information to resolve the origin, transport, and conversion of environmental methane. We used a high-resolution mass spectrometer (Thermo Fisher Scientific 253 Ultra) to precisely determine Δ13CH3D and Δ12CH2D2 (precision and accuracy of ∼0.35‰ and ∼1.35‰ (1σ), respectively) in this study. The impacts of temperature, humidity, and slit quality are found to be critical for the reproducibility of the results, while the fragmentation rate and bellows effects on the clumped isotope results were negligible. A heating equilibrium experiment performed at 500 °C, 400 °C and 300 °C (n = 19) calibrates the results to an absolute reference. A pretreatment system that can extract methane having concentrations from ∼15% to ∼99.8% is proposed, while the fractionation produced throughout the pretreatment is negligible within precision (Δ13CH3D = +0.16 ± 0.32‰ and Δ12CH2D2 = +0.14 ± 1.12‰ (n = 16)). Analyses of natural gases from shale basins and variable methane-rich gases emitted from artificial lakes validate the capability of the current pretreatment and spectrometer systems to determine methane clumped isotopes in a wide range of natural environmental samples. [ABSTRACT FROM AUTHOR]

Floods in global large rivers modulate the transport of dissolved organic carbon (DOC) and estuarine hydrological characteristics significantly. This study investigated the impact of a severe flood on the sources and age of DOC in the Yangtze River Estuary (YRE) in 2020. Comparing the flood period in 2020 to the non-flood period in 2017, we found that the flood enhanced the transport of young DOC to the East China Sea (ECS), resulting in significantly enriched Δ14C-DOC values. During the flood period, the proportion of modern terrestrial organic carbon (OC) was significantly higher compared to the non-flood period. Conversely, the proportion of pre-aged sediment OC was significantly lower during the flood period. The high turbidity associated with the flood facilitated rapid transformation and mineralization of sedimentary and fresh terrestrial OC, modifying the sources of DOC. The flux of modern terrestrial OC transported to the ECS during the flood period was 1.58 times higher than that of the non-flood period. These findings suggest that floods can modulate the sources and decrease the age of DOC, potentially leading to increased greenhouse gas emissions. Further research is needed to understand the long-term impacts of floods on DOC dynamics in global estuaries. [Display omitted] • The flood enhances the transport of young DOC in the YRE. • The flood modulates the sources of DOC in the YRE. • The proportion of modern terrestrial OC is higher during the flood period. • The high turbidity associated with the flood promotes the transformation of young OC. • The flux of modern terrestrial OC during the flood period is 1.58 times higher. [ABSTRACT FROM AUTHOR]

[Display omitted] • Coal and amendments significantly increase methane production in incubation. • Machine learning help predict missing biogenic Δ12CH 2 D 2 data. • Clumped isotopes indicate differential reversibility and combinatorial effects. • Coal bioavailability rather than coal thermal maturity determine CH 4 production. Biogenic (microbial) methane is an imperative natural gas resource and plays an important role in the global carbon cycle. Determining isotope systematics in microbially enhanced coal bed methane (MECBM) informs methane biogeochemical processes and environmental impacts. Here, we conduct laboratory MECBM experiments using coal samples of differing maturities (from lignite to anthracite) and report analytical results of methane production, bulk and clumped isotopes (δ13C, δD, Δ13CH 3 D and Δ12CH 2 D 2). We reproduce the differential reversibility in methanogenic reactions, which exhibits a correlation with kinetic clumped isotope fractionation (Δ13CH 3 D from +0.17 ‰ to +4.04 ‰). The exogenous combinatorial effects play a greater role in determining the negative Δ12CH 2 D 2 (<–30 ‰). In the microcosm of MECBM, coal and amendments are suggested to significantly increase methane production (from 82.4 ± 17.1 to 344.6 ± 22.8 μmol CH 4 /g coal), with effects controlled by substrate coal bioavailability rather than coal thermal maturity. This suggests the possibility of MECBM attempts to utilize high thermal maturity coal. We perform machine learning models and improve the accuracy of biogenic 12CH 2 D 2 predictions, which help understand the mechanism of methane formation, and further provide new insights into clumped isotope effects among different biogenic methane sources. Our incubation experimental and compiled dataset (n = 275) better constrain biological participation in the methane formation process and potentially be used for methane sources tracing. [ABSTRACT FROM AUTHOR]

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]

• 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]

[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]

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]

• 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]

• 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]

• 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]

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]

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]