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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]

• Using δ13C DIC and water chemistry to refine the sources and multiple processes in the waters. • A new model to understand migration and transformation of DIC in a karst river-reservoir system. • HRT is a key factor for carbon transportation and transformation in the reservoir. In order to advance our understanding of the driving factors controlling carbon dynamics and evolution of water quality in river-reservoir systems for the generation of hydropower, we conducted a study in a karst deep-water reservoir (Wujiangdu Reservoir), southwest China. Water samples were collected from the inflow/outflow of the Wujiangdu Reservoir, four vertical columns along the reservoir, and from three tributaries to the reservoir in January, April, July, and October 2017. The dissolved inorganic carbon (DIC) concentrations and carbon isotope composition (δ13C DIC) varied greatly (1.99–3.45 mmol/L and −10.7‰ to −6.0‰, respectively) and were controlled by multiple processes including CO 2 outgassing, primary production, and organic matter degradation. In the four vertical profiles, the difference between the values of samples with those at 15 m of Δ[DIC] and Δ[δ13C DIC ], Δ[DIC] and ΔCa2+ in the same water column had positive correlations, and the variation in dissolved O 2 , partial pressure of CO 2 , and flux of CO 2 suggested that primary production dominated above the epilimnion and degradation of OM dominated below the epilimnion during the warm season. Continuous CO 2 outgassing was found from riverine water to surface water of the reservoir before the dam based on carbon isotopic compositions and water chemistry. These processes would cause isotopic fractionation between the residual DIC and CO 2 (aqueous), the degree of which varied among different seasons (July > April > October > January). Carbon transport and biogeochemical processes were highly controlled by the hydraulic retention time (HRT) in the river-reservoir system. It was estimated that approximately 71.5% of the annual DIC flux was produced in the water column below 15 m depth during the study year, suggesting that the processes of DIC generation and consumption occurred at the same time. The results highlight that carbon behavior in the impounded rivers is influenced by multiple processes. The carbon transformation processes should be taken into account for improving the estimation accuracy of the carbon budget calculations and the management of water quality for river-reservoir systems. [ABSTRACT FROM AUTHOR]

Abstract Coupled nitrogen and oxygen isotopes of nitrate have proven useful in identifying nitrate sources and transformation in rivers. However, isotopic fractionation and low-resolution monitoring limit the accurate estimation of nitrate dynamics. In the present study, the spatio-temporal variations of nitrate isotopes (15N and 18O) and hydrochemical compositions (NO 3 − and Cl−) of river water were examined to understand nitrate sources in the Xijiang River, China. High-frequency sampling campaigns and isotopic analysis were performed at the mouth of the Xijiang River to capture temporal nitrate variabilities. The overall values of δ15N-NO 3 − and δ18O-NO 3 − ranged from +4.4‰ to +14.1‰ and from −0.3‰ to +6.8‰, respectively. The results of nitrate isotopes indicated that NO 3 − mainly originated from soil organic nitrogen (SON), chemical fertilizer (CF), and manure and sewage wastes (M&S). The negative correlation of nitrate isotopic values with NO 3 −/Cl− ratios suggested the importance of denitrification in NO 3 − loss. The results of Bayesian model with incorporation of isotopic fractionation during the denitrification showed that SON and CF contributed to the most (72–73%) nitrate in the wet season; whereas approximately 58% of nitrate was derived from anthropogenic inputs (M&S and CF) in the dry season. The nitrate flux was 2.08 × 105 tons N yr−1 during one hydrologic year between 2013 and 2014, with 86% occurring in the wet season. Long-term fluctuations in nitrate flux indicated that nitrate export increased significantly over the past 35 years, and was significantly correlated with nitrate concentrations. The seasonal pattern of nitrate dynamics indicated the mixing of nitrified NO 3 − and denitrified NO 3 − between surface flow and groundwater flow under different hydrological conditions. Overall, the present study quantitatively evaluates the spatio-temporal variations in nitrate sources in a subtropical watershed, and the high-frequency monitoring gives a better estimate of nitrate exports and proportional contributions of nitrate sources. Graphical abstract Unlabelled Image Highlights • Evaluate spatio-temporal contributions of nitrate sources by Bayesian mixing model. • Identify temporal nitrogen dynamics by high-frequency analysis of nitrate isotopes. • Nitrate concentrations determine the long-term pattern of nitrate flux. [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]

In this study, a novel coumarin-derived compound bearing the furan moiety called 7-diethylamino-3-formylcoumarin (2′-furan formyl) hydrazone ( 1 ) has been designed, synthesized and evaluated as a Zn 2 + ratiometric fluorescent probe in ethanol-water system. This probe 1 showed good selectivity and high sensitivity towards Zn 2 + over other metal ions investigated, and a decrease in fluorescence emission intensity at 511 nm accompanied by an enhancement in fluorescence emission intensity at 520 nm of this probe 1 was observed in the presence of Zn 2 + in ethanol-water (V : V = 9 : 1) solution, which provided ratiometric fluorescence detection of Zn 2 + . Additionally, the ratiometric fluorescence response of 1 to Zn 2 + was nearly completed within 0.5 min, which suggested that this probe 1 could be utilized for sensing and monitoring Zn 2 + in environmental and biological systems for real-time detection. [ABSTRACT FROM AUTHOR]

In this study, a novel chromone-derived Schiff-base ligand which was called bis(6-hydroxychromone-3-methylidene)- o -phenylenediimine ( 1 ) was designed, synthesized, and evaluated as an Al 3+ “turn on” fluorescent probe. This probe 1 showed good selectivity and high sensitivity towards Al 3+ in the presence of most metal ions, and a remarkable enhancement by about 30.91-fold in fluorescence emission intensity at 459 nm was observed with addition of 1 equiv of Al 3+ , which was attributed to the inhibition of photoinduced electron-transfer (PET) phenomenon and C N isomerization process at the excited state. Moreover, the fluorescence response of 1 to Al 3+ was nearly completed within 10 min. Thus, this probe 1 could be utilized for sensing and monitoring Al 3+ in environmental and biological systems for real-time detection. [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]

Isotopic compositions of the water sources and evapotranspiration in large rivers of China are not well explored. In this investigation, δO and δD values of water from major large rivers of China are integrated to understand the spatial and temporal variations in the isotopes of water and d-excess. River water samples were collected from the channels and tributaries of the Changjiang, Yellow, Songhua, and Liao Rivers in China. Water from upstream was generally enriched with light isotopes relative to that from downstream areas. Water from the Songhua River and upper reach of the Changjiang River has relatively negative isotopic values, impacted by latitude and altitude effects, respectively. The spatial pattern showed that δO-HO values in rivers mainly ranged from −9 to −7 ‰ in most of China based on roughly mapped contours, and rivers enriched in light isotopes were primarily located in the Tibetan Plateau and northeast China. The slopes of linear regression from the Yellow and Liao Rivers suggested that the loss of water by direct evaporation shifted the isotopes of water, especially in some small tributaries. Additionally, there was a narrow range of low δO-HO values from the main channel of rivers during the low-flow season relative to the high-flow season due to influence of the monsoon climate. No distinct spatial variation of d-excess values was found in the rivers of China. However, water samples in some rivers with low d-excess values had high δO values, indicating that evaporation in the tributaries has led to significant water loss, especially in tributaries of the Yellow and Liao Rivers. [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]

Highlights: [•] Water chemistry and isotopes (δ34S, δ18O, δ13C) reveal the weathering process. [•] 72% of sulphate derived from sulphide oxidation in the Yalong River. [•] Dynamics of DIC affected by carbonate weathering and equilibration processes. [•] Sulphuric acid dominate carbonate weathering in the cold and dry zone with high elevation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nitrate was the dominant species of DIN in Liao River. [•] High fraction of /DIN observed during low flow season. [•] Nitrate in rivers originated mainly from nitrification and sewage based on isotopic pattern. [•] About 7.0×104 tonN/yr entered the Bay annually amounting to 5% of N fertilizer. [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]

Abstract: The sources of dissolved inorganic carbon (DIC) and rock weathering processes were studied in the Houzhai catchment, a typical karstic catchment in the Changjiang River Basin, Southwest China. The carbon isotopic compositions (δ 13CDIC) of DIC in the samples collected from the catchment vary from −13.5‰ to −6.9‰, with a mean value of −9.8‰. The DIC in the catchment is thereby considered to be mainly derived from soil CO2 and weathering of carbonate rocks. The DIC concentrations and the δ 13CDIC values show pronounced seasonal variations, with the lowest values being observed during the high flow season (from May to October). The logPCO2 values in the waters were positively correlated with the DIC contents and negatively correlated to the saturation index of calcite (SIc) and δ 13CDIC values. These observations indicate that CO2 derived from organic matter oxidation plays an important role in the dissolution of carbonate for this typical karstic environment. Based on a chemical mass balance, the weathering rate of carbonate rocks in the Houzhai catchment was estimated to be approximately 133t/km2/year or 584×103 mol/km2/year in terms of CO2 consumption rate, which is higher than the reported values for other rivers in Southwest China. [ABSTRACT FROM AUTHOR]

Abstract: Rock weathering by carbonic acid is thought to play an important role in the global carbon cycle because it can geologically sequestrate atmospheric CO2. Current model of carbon cycle evolution usually assumes that carbonic acid is the major weathering agent and that other acids are not important. Here, we use carbon isotopic evidence and water chemistry of springs and rivers from the Beipanjiang River basin (Guizhou Province, Southwest China) to demonstrate that sulfuric acid is also an important agent of rock weathering. The δ 13C of dissolved inorganic carbon (DIC) in the water samples ranges from −13.1‰ to −2.4‰, and correlates negatively to [HCO3 −]/([Ca2+]+[Mg2+]) ratios and positively to [SO4 2−]/([Ca2+]+[Mg2+]) ratios. These relationships are interpreted as mixing diagrams between two reactions of carbonate weathering, using carbonic acid and sulfuric acid as a proton donor, respectively. Mixing proportions show that around 42% of the divalent cations in the spring water from Guizhou are originated from the interaction between carbonate minerals and sulfuric acid. It is shown that 40% of this sulfuric acid is derived from the atmosphere and has an anthropogenic origin. The remaining 60% are derived from the oxidative weathering of sulfide minerals in sedimentary rocks. Our results show the positive action of sulfuric acid on the chemical weathering of carbonate. Particularly, we show that sulfuric acid generated by coal combustion has increased by almost 20% the weathering rates of carbonate in Southwest China. This is a clear evidence that human activities are changing the weathering rates of rocks and demonstrates a negative feedback on the acidification of the ocean by greenhouse gases. Because of the involvement of sulfuric acid in weathering reactions, 63% of the alkalinity exported by rivers is derived from carbonate, instead of 50% when atmospheric CO2 is the only acid involved in chemical weathering of carbonate. In the Guizhou Province, the weathering of carbonate is thus, at least transiently, a net source of CO2 to the atmosphere. When extrapolated at global scale, sulfuric acid-induced carbonate weathering could counterbalance a significant part of the CO2 consumed by silicate weathering. This paper highlights the competition between silicate weathering by carbonic acid and carbonate weathering by sulfuric acid for the regulation of the atmospheric CO2 level. [Copyright &y& Elsevier]

[Display omitted] • Significant temporal variations of carbon concentrations and δ13C DIC were observed. • Short-term climate variability plays an important role in carbon dynamics. • Biological carbon influxes should be responsible for the seasonal carbon dynamics. • The carbon-climate feedback is sensitive for the two rivers. Carbon-climate feedback is sensitive in the Qinghai-Tibet Plateau. A series of temporal measurements from Jinsha River and Yalong River, in conjunction with flow information, were used to study the carbon dynamics and predict future carbon fluxes under ongoing climate change. DIC and DOC concentrations showed considerable temporal variations, with low DIC and high DOC concentrations in the high-flow season, and vice versa. DIC and DOC concentrations had negative and positive relationships with runoff changes, respectively, showing the hydro-biogeochemical controls on carbon dynamics. With the increase of runoff, the accelerated chemical weathering and the high carbonate buffering capacity should be responsible for the chemostatic behaviors of DIC. Meanwhile, warm weather would enhance organic carbon degradation, and also thicken the active layer of permafrost in the source area, both of which would produce DOC. In addition, organic carbon degradation in the high-flow season would produce DIC with 13C-depleted values. δ13C DIC also had significant temporal variations, synchronous with runoff changes (i.e., light values under high runoff conditions), supporting that biological carbon plays an important role in carbon dynamics during the warm season. Based on the clear positive correlations between carbon fluxes and runoff, we predicted that the sensitivities of DOC fluxes to temperature changes are 12.2%/°C and 8.3%/°C for the Jinsha River and Yalong River, respectively. The sensitivities of DIC fluxes to temperature changes are much lower, which are 5.5%/°C and 6.1%/°C for the Jinsha River and Yalong River, respectively. This study sheds lights on the alpine riverine carbon cycling based on runoff-shifting concentration-isotope (q - C - I) relationships in the Qinghai-Tibet Plateau, which has implications on the understanding of climate forcing on carbon fluxes in alpine areas. [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]

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

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

• Agriculture in karst hills is more likely to cause more soil and nutrient losses. • Karst structure might lead to fast nutrient loss and low fertilizer use efficiency. • Results suggest nutrient losses controlled by landform and climate condition. • Carbonate weathering and carbon cycle are strongly impacted by agriculture in karst regions. • Beneficial management practices should be considered for sustainable development. The karst region in southwestern China is a typical region with fragile ecological environments, and the coordination of regional agricultural development and environmental protection faces enormous challenges. Based on the soil and hydrological characteristics of karst in southwestern China, this study summarized water-related environmental issues caused by agricultural activities in this karst region. Agriculture in the karst hills is more likely to cause soil and nutrient losses due to the fast hydrological flow through special karst structures with high permeability. Thus, this review emphasized the impacts of agricultural development on the riverine biogeochemical cycles of elements based on previous studies. Meanwhile, the carbon cycle is also strongly impacted by agricultural activities in this karst region due to enhanced carbonate weathering by nitric acid from the nitrification of ammonium. This weathering mechanism represents a net source of atmospheric CO 2 and might impact regional and global carbon cycling in the Anthropocene. Based on the results summarized in this study, we advocate that in the future, better management of agricultural land, improvement of fertilizer use efficiency, and boosting of nutrient recycling rate should be taken into account for reducing nutrient losses and water quality deterioration. Targeted management of local agricultural practices along with guidance from scientific research results is needed to be devoted to sustainable development of agriculture and economies while protecting water environment. [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]

• The relationships between landscape patterns and water quality are scale-dependent. • Water quality variation is better explained by landscape pattern at catchment scale. • The influence of landscape pattern on water quality is stronger in the dry season. • Geographical characteristics influence water quality by interacting with land use. Understanding the spatially varying relationships between landscape pattern and water quality in the agricultural karst river system is helpful for landscape planning and management to protect water quality. In this study, empirical models were established to examine the impact of landscape pattern on the seasonal water quality at multi-spatial scales in a typical karst river basin in Southwestern China. Water samples from the Chishui River basin were collected and analysed during both the wet and dry seasons. Kruskal–Wallis tests revealed significant seasonal variations in water physic-chemical parameter variables, the values of which were all generally higher in the wet period than those in the dry period except for pH and SO 4 2−. Moreover, the nutrient indicators including NO 3 −-N, PO 4 3−-P, DOC and DSi showed obvious spatial variations, some of which were related to the spatial distribution of cropland that reflected the agricultural activities of the basin. Redundancy analysis results indicated that the landscape pattern metrics can better explain the variation of water physic-chemical parameters in the dry period than in the wet period. The results revealed that the overall variations of water physic-chemical parameters were better explained by landscape pattern metrics at catchment scales. Further, the results of multiple linear regression model showed that the scale effects of the relationship between landscape pattern and water quality varied across different metrics and parameters. The geographical characteristics of catchment had significant relationships with some water physic-chemical parameters, suggesting that it may have impacts on water quality through combining with land use. This study highlights the importance of spatial scale in reflecting land-water interactions. [ABSTRACT FROM AUTHOR]

• Nutrient allocation of mulberry leaves impacted by P availability in the karst area. • Mulberry leaf development was limited by N availability at the late stage. • Plant absorbs different N species during various growth stages based on isotopes. • N was more important than P for Zn allocation in mulberry leaves under N deficiency. It is important to understand nutrient-use-efficiency based on the interaction between nutrient allocation and plant growth. This study utilized mulberry (Morus spp.), an economically important plant for farmers, as an example, to investigate the effect of nutrient allocation on plant growth and its response to environmental conditions in the karst region of Southwest China. Leaf stoichiometric analysis and isotopic measurements were applied to reveal the causes and effects of the allocation of different nutrients. The results illustrated that the N:P ratios of mulberry leaves decreased as the mean temperature increased and plant tissues grew, exhibiting a high leaf N:P ratio (21.82 ± 6.33) at the early stage of leaf expansion, and a low ratio (10.70 ± 2.66) at the late stage of leaf development. The low leaf N:P ratios indicated that leaf development was largely limited by nitrogen availability as the plant grew. The slight difference of δ15N between leaf and root (leaf-root δ15N, −0.30 ‰) implied that the mulberry preferred ammonium-N at the early stage of leaf development, while the large difference of leaf-root δ15N (1.58 ‰) implied that the mulberry preferred nitrate-N at the late stage. Although the ammonium uptake could improve P availability by increasing soil pH value deficiency at the early stage of leaf expansion, plant growth was constrained by P availability, given the relatively high P uptake from soils and the large P allocation in leaves. Moreover, the allocations of N and P were strongly correlated with other nutrients allocations. P exhibited strongly positive effects on Ca and K allocations under P deficiency at the early stage of leaf expansion, while N presented important impacts on them under N deficiency at the late stage. To summarize, this study highlighted the interactions between allocations of different nutrient components which are related to plant growth and environmental conditions in the karst system. [ABSTRACT FROM AUTHOR]

Hydrochemical behavior and dissolved carbon dynamics are highly-sensitive to hydrological variations in the monsoon-influenced karstic critical zone which has high chemical weathering rates and experiences strong anthropogenic impact. Continuous high-frequency monitoring in the spring outlet of a karstic catchment in Southwestern China revealed that most hydrochemical variables changed distinctively in response to hydrologic variations, influenced by mixing of different sources and miscellaneous biogeochemical processes. Na+, K+ and SO 4 2− varied significantly with hydrology, showing weak chemostatic behavior controlled by dilution. The flushing effect and random behavior of NO 3 − and Cl− likely reflect agricultural inputs from high throughflow. Soil CO 2 in infiltrated water supports carbonate weathering, enabling DIC (dissolved inorganic carbon) and weathering products (e.g., Ca2+ and Mg2+) to maintain chemostatic behavior. Biogenic DIC exhibited a stronger chemostatic response than carbonate sources and was the foremost control in DIC behavior. Carbon exchange between DIC and DOC (dissolved organic carbon) did not significantly influence DIC concentration and δ13C due to very low DOC concentration. More DOC was exported by flushing from increasing discharge. Hysteretic analysis indicated that the transport processes were controlled by proximal sources mixing and diverse mobilization in various periods responding to rainstorms. NO 3 − and Cl− presented different hysteresis behavior as sourced from agricultural activities. DOC increased on the hydrograph rising limb and was controlled by a transport-limited regime. However, the hysteresis behavior of most weathering products and DIC were regulated by a process-limited regime in the karstic critical zone. Overall, biogeochemical processes, hydrogeological properties, storm intensity/magnitude and the timing of storms (antecedent conditions) are main factors influencing the response of hydrochemical variables and dissolved carbon to storm events. Unlabelled Image • High-resolution data reveal the chemostatic behavior of HCO 3 −, Ca2+ and Mg2+. • NO 3 − and Cl− are affected by throughflow flushing and show randomness behavior. • Biologically-derived DIC controls DIC behavior during high discharge condition. • DOC and DIC are regulated by transport-limited and process-limited, respectively. • Hydrogeology, storm intensity and antecedent conditions affect solutes behavior. [ABSTRACT FROM AUTHOR]

• Nitrogen accumulated in dry condition and was flushed into river by rainfall events. • Nutrient dynamics are dependent on interaction of hydrology with source availability. • Nitrogen transformation processes are more active under the wet conditions. • Scientific fertilization and planning of cropping are advised for water NO 3 − control. High discharge associated with rainfall events causes rapid transport of nutrients to drainage systems in karst terrain. The objective of this study was to understand nitrate dynamics and transport mechanisms during rainfall events in a typical mixed land-use karst catchment in Southwest China. High frequency (hourly) water sampling, discharge and hydrochemistry sensor data at a 15-minute interval were collected from a karst agricultural surface river over four rainfall events, spanning 40 days at the commencement of the wet season. The results showed that high [NH 4 +–N] (up to 3.12 mg L−1) and [PO 4 3−– P] (up to 1037 μg L−1) were observed in the first rainfall event of the wet season, after a long preceding dry period. Increased [NO 3 −–N] also occurred during the high discharge associated with early event flows, but the highest [NO 3 −–N] concentrations (up to 14.9 mg L−1) were observed later in the season during the highest discharge events. All minima for dual nitrate isotopes were found during high discharge conditions and increased through the event time series. This indicates that nitrogen accumulated in the catchment prior to the commencement of the wet season and was flushed by the early rainfall events into the drainage system. Analysis of [NO 3 −–N], δ 15N and δ 18O-NO 3 − values indicate that denitrification, not assimilation, resulted in the high nitrate isotope values before and after rainfall events. According to source apportionment, chemical fertilizer, soil organic nitrogen, and manure and sewage, which varied with discharge, were the main sources of nitrate during rainfall events. The high proportion of nitrate from soil organic nitrogen suggested that soil loss from peak clusters and lowland farmland during heavy rainfall events should be paid more attention in karst area. [ABSTRACT FROM AUTHOR]

The effect of dams on dissolved inorganic carbon (DIC) transport and riverine ecosystems is unclear in karst cascade reservoirs. Here, we analyzed water samples from a karst river system with seven cascade reservoirs along the Wujiang River, southwestern China, during one hydrological year. From upstream to downstream, the average concentration of DIC increased from 2.2 to 2.6 mmol/L and its carbon isotope composition (δ13C DIC) decreased from −8.0 to −10‰. Meanwhile, the air temperature (Ta) increased from 20.3 °C to 26.7 °C and 10 °C to 13.7 °C in the warm and cold seasons, respectively. The results suggest that a cascade of dams has a stronger effect on DIC dynamics and retention than a single dam. The good correlation between Ta/HRT (hydraulic retention time) and Δ[DIC] as well as Δ[δ13C DIC ] mean that Ta and HRT affected the magnitude of the damming effect by altering changes in concentration of DIC and δ13C DIC in the reservoir compared to the inflowing water. In particular, daily regulated reservoirs with short retention times acted more like river corridors and had a smaller effect on carbon dynamics, so modulating retention time might be used reduce the effect of dams on the riverine ecosystem. Unlabelled Image • DIC concentrations and δ13C DIC trends were investigated across cascaded reservoirs. • Carbon dynamics in the reservoirs were mainly impacted by biological processes. • Damming effect is controlled by both hydraulic retention time and air temperature. • The damming effect can be weakened by regulating the hydraulic retention time. [ABSTRACT FROM AUTHOR]

Emission of reactive nitrogen species has a major impact on atmospheric chemistry, ecosystem and human health. The origin and formation mechanisms of wet-deposited nitrate are not well understood in Southeast Asia (SEA). In this study, we measured stable isotopes of nitrate (δ15N and δ18O) and chemical compositions of daily rainwater from May 2015 to July 2017 in Singapore. Our results showed that δ15N–NO 3 − and δ18O–NO 3 − varied seasonally with higher values during the Inter-monsoon period (April–May and October–November) than during Northeast (December–March) and Southwest monsoon (June–September). Bayesian mixing modeling, which took account of the isotope fractionation, indicated that traffic emission (47 ± 32%) and lightning (19 ± 20%) contributed the most to NO 3 − with increased traffic contribution (55 ± 37%) in the Northeast monsoon and lightning (24 ± 23%) during the Inter-monsoon period. Biomass burning and coal combustion, likely from transboundary transport, contributed ∼25% of nitrate in the rainwater. Monte Carlo simulation of δ18O–NO 3 − indicated that oxidation process by hydroxyl radical contributed 65 ± 14% of NO 3 −, with the rest from hydrolysis of N 2 O 5. Wind speed had large effect on δ18O–NO 3 − variations in the atmosphere with more involvement of hydroxyl radical reactions when wind speed increased. Our study highlights the key role of isotopic fractionation in nitrate source apportionment, and the influence of meteorological conditions on nitrate formation processes in SEA. Image 1 • δ15N–NO 3 − and δ18O–NO 3 − of rainwater varied seasonally in Singapore. • Traffic emission contributed the most to atmospheric NO 3 − in NE monsoon. • Nitrate formation process is strongly influenced by meteorological conditions. • Nitrate source apportionments were impacted by the secondary processes. [ABSTRACT FROM AUTHOR]

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

Hydrochemical behaviour and dissolved carbon dynamics have high sensitivity to hydrologicvariations during high-flow periods in monsoonal-influenced regions, especially inthe critical zone of agricultural karstic catchment where existing anthropogenicinterference and carbonate weathering with rapid kinetics. Here we selected Chenqicatchment, a 1.5 km2 sub-catchment of Houzhai basin in Puding, SW China, as studyarea to analyze the response of hydrochemistry and dissolved carbon dynamicsto discharge changes, through hourly sampling campaigns in the outlet of springwater during the high-flow period. Most dissolved ions exhibit distinct responsesto discharge variations, their concentrations are negatively correlated with springwater discharge, which can be well fitted using power-law function, indicating theirchemostatic behaviours as discharge increases, but biogeochemical processes influencingdifferent ions are miscellaneous. Ca2+, Mg2+ and HCO3− are mainly controlled bydissolved soil CO2 and carbonate weathering, while NO3− and Cl− both haveanthropogenic inputs and may exist some link about their source areas or transport processesactivated during high-flow periods. Other ions are generally affected by the dilution ofrainwater. Hydrological conditions and biogeochemical processes regulate dissolvedcarbon dynamics, resulting in the variation of δ13CDIC. There are two sources forDIC in spring water of Chenqi catchment, namely biological source (DICbio) andgeological source (DICcarb). The contribution ratio of DICbio is around thrice that ofDICcarb, and they both show chemostatic response to varying discharge althoughthe degrees for DICbio is stronger. The response of dissolved carbon dynamics todischarge variations display different degrees at different stages of the wet season. Itwas find that most dissolved solutes (except DOC) normally present clockwisehysteresis loops plotting from the top-left to bottom-right due to the dilution onthe rising limb of the storm, but the loop area and hysteresis index are differentwithin or between diverse storms. The pattern is related to rain intensity/amount andantecedent conditions, which can affect flow pathways and likely source areas, leadingto different transport time and loads. These hysteresis behaviours are generallycontrolled by antecedent conditions of storms, range/peak of discharge and soluteconcentrations, and storm duration. Overall, this study highlighted the sensitivecharacteristics of hydrochemistry and dissolved carbon dynamics to hydrologicalvariations in small agricultural karstic catchment based on high resolution information. [ABSTRACT FROM AUTHOR]

Extensive anthropogenic activities have resulted in increased delivery of reactive nitrogen to rivers and streams, which can cause aquatic pollution and increase human health risks. Thus, it is important to identify the sources and fate of nitrate for water quality management. Stable isotopes of nitrate have been widely used to evaluate biogeochemical behavior of nitrate in aquatic ecosystem. However, isotopic fractionation and low-resolution monitoring limit the accurate estimation of nitrate sources. Here, we collect river water and conduct a high-time resolution measurement of isotopic analysis (δ15N-NO3− and δ18O-NO3−) in the Xijiang River, Southwest China. The Xijiang watershed covers approximately 77.8% of the drainage basin area of the Pearl River watershed. It has abundant water resources, with an average discharge of 2.30 × 1011 m3 yr−1. The studied watershed belongs to a subtropical humid monsoon climate with annual air temperature changing from 14°C to 22°C. The mean annual precipitation varies from 1,200 mm to 2,200 mm with mainly concentrated from April to September (wet season). The contribution ratios of nitrate sources are calculated using a Bayesian isotope mixing model (SIAR) by incorporating isotopic fractionation. The δ15N-NO3− and δ18O-NO3− vary seasonally with higher δ15N-NO3− (+8.4 ± 1.6‰) and lower δ18O-NO3− (+2.0 ± 1.4‰) in the dry season compared with those of wet season (+7.6 ± 1.6‰ for δ15N-NO3− and +2.7 ± 1.4‰ for δ18O-NO3−). The isotope values of NO3− vary greatly under different discharge conditions in the wet season, highlighting the importance of high-time resolution measurement especially in the wet season. The outputs of Bayesian model indicate that soil organic nitrogen and chemical fertilizer contribute the most (72−73%) in the wet season; whereas approximately 58% of nitrate is derived from manure and sewage wastes and chemical fertilizer in the dry season. This study combines hydrochemistry, stable isotopes with multi-statistical method, and make important progress in accurate estimation of nitrate dynamics in river. [ABSTRACT FROM AUTHOR]

Tectonically active high relief areas are proposed to have a substantial impact on climate regulation throughout the Cenozoic. Here, we present lithium (Li) isotope data of the dissolved load and suspended particulate material from the basins of the Yalong River and the Jinsha River, which drain the high-relief borders of the eastern Tibetan Plateau and constitute the headwaters of the Yangtze River. Dissolved δ7Li values are relatively low and constant in the Jinsha River mainstream (+6.8‰ to +9.7‰) compared to the higher and downstream increasing values in the Yalong River mainstream (+10.8‰ to +17.5‰). Furthermore, dissolved δ7Li values in the major tributaries of the Jinsha and Yalong River are highly variable and increase downstream from +11.4‰ to +29.4‰ and from +9.0‰ to +23.6‰, respectively. Robust correlations between Li, Na, and Cl concentrations identify that evaporite dissolution in the uppermost headwaters of the Jinsha River basin controls the Li budget and riverine δ7Li values of the mainstream and has a significant impact on dissolved Li in the Yangtze River. In contrast to the Jinsha River mainstream, dissolved Li in the Yalong River mainstream and the Jinsha and Yalong River tributaries are dominantly derived from the dissolution of silicates. δ7Li variations in the Yalong River basin and the Jinsha tributaries reflect little Li uptake by clays in the upper reaches and more Li uptake by clays in the lower reaches of the river basins. SWR/D ratios (where SWR is the chemical silicate weathering rate, and D is the total denudation rate) highlight an intermediate silicate weathering intensity under a kinetically limited weathering regime for the study area. However, positive correlations between dissolved δ7Li value and silicate weathering intensity proxies (such as Si/(Na sil + K) and K/(Na sil + K)) indicate an increasing weathering intensity downstream. A positive correlation between dissolved δ7Li values and the annual precipitation and a negative one between δ7Li values and elevation indicates that larger annual precipitation under a flattening relief results in a stronger silicate weathering intensity, thus, more Li uptake in clays and higher riverine δ7Li values in the lower reaches. Compared to the lower reaches of Yangtze River basin (∼+20‰), lower dissolved δ7Li values in its headwater of this study suggest that the increase in δ7Li of seawater over the Cenozoic is influenced by weathering in floodplains that developed due to erosion of high mountains, rather than weathering of mountain belts itself. Combined with silicate weathering rates of the eastern border of the Tibetan Plateau, the highest riverine δ7Li values in its catchments come along with the highest silicate weathering rates and high CO 2 consumption, suggesting that a more elevated topography may have an important role in the drawdown of CO 2 during the Cenozoic. [ABSTRACT FROM AUTHOR]

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

In this study, a novel 1,8-naphthalimide derived compound bearing the coumarin moiety called 7-Diethylaminocoumarin-3-aceone ( N -hydroxyethyl-1’,8’-naphthalimide-4’-) hydrazone ( 1 ) has been designed, synthesized and evaluated as a dual-functioning fluorescent probe for “turn-off” and ratiometric detection of Cu 2+ based on two distinct mechanisms in different concentration ranges in aqueous solution. This probe 1 showed high selectivity and sensitivity for Cu 2+ over other common metal ions, for the limit of detection (LOD) could reach 3.90 × 10 −8 M and 3.26 × 10 −7 M for “turn-off” and ratiometric detection respectively. Moreover, in Cu 2+ equivalence range of 0–0.5, a decrease in fluorescence emission intensity at 441 nm was observed upon addition of Cu 2+ , but in Cu 2+ equivalence range of over 0.5, a new emission band centered at 462 nm appeared with increasing intensity accompanied by a decrease in fluorescence emission intensity at 570 nm, which provided ratiometric fluorescence detection of Cu 2+ . The sensing mechanisms for the responses of 1 to Cu 2+ were chelation-quenched fluorescence (CHQF) and chemical reaction between 1 and Cu 2+ over Cu 2+ equivalence range of 0–0.5 and more than 0.5, respectively. Thus, this probe 1 could be utilized for sensing and monitoring Cu 2+ in environmental and biological systems in different concentration ranges. [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]

By using the coupled model of Hindmarsh—Rose neuronal systems, we numerically investigate the effect of topology structures on the firing patterns transition (FPT). A four-cell coupled system with all possible configurations are studied. We select the membrane current Iext as a controllable parameter, and set it to be near the left side for one of the bifurcation points. It is found that to have a response from some external stimuli with the proper amplitude and frequencies, the transition will appear between different firing states only when the cells in the system are coupled with some proper topological structures, which implies the occurrence of FPT induced by the configuration in the coupled system. Similar FPT phenomena could also be observed in a five-cell coupled system. Furthermore, we find that such transition behaviors may have some inherent relevance with the synchronization error and the average connective number among cells in the coupled system for different topology structures. These results suggest that the biological neuron systems may achieve an effective response to the external feeble stimulus by selecting the proper configuration and using the corresponding transition mode. [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]