Search

Catalpa bungei is a precious timber species distributed in North China where drought often occurs. To clarify adaptive responses of C. bungei to partial- and full- root-zone drought under the influence of nitrogen forms, a two-factor experiment was conducted in which well-watered (WW), partial root-zone drought in horizontal direction (H-PRD) and in vertical direction (V-PRD), and full root-zone drought (FRD) were combined with nitrate-nitrogen (NN) and ammonium-nitrogen (AN) treatments. C. bungei responded to FRD by sharply closing stomata, decreasing gas exchange rate and increasing leaf instantaneous water use efficiency (WUEi). Under FRD condition, the growth of seedlings was severely inhibited and the effect of N forms was covered up by the drastic drought effect. In comparison, stomata conductance and gas exchanges were moderately inhibited by PRDs. WUEi in V-PRD treatment was superior to H-PRD due to the active stomata regulation resulting from a higher ABA level and active transcription of genes in abscisic acid (ABA) signaling pathway under V-PRD. Under both PRDs and FRD, nitrate benefited antioxidant defense, stomata regulation and leaf WUEi. Under V-PRD, WUEi in nitrate treatment was superior to that in ammonium treatment due to active stomata regulation by signaling network of nitric oxide (NO), Ca2+ and ABA. Under FRD, WUEi was higher in nitrate treatment due to the favoring photosynthetic efficiency resulting from active NO signal and antioxidant defense. The interactive effect of water and N forms was significant on wood xylem development. Superoxide dismutase (SOD) and catalase (CAT) largely contributes to stress tolerance and xylem development. [ABSTRACT FROM AUTHOR]

Typical sources of nitrate pollution in the fragile ecological environment of karst areas, such as agricultural production activities and domestic sewage, have long attracted serious concern. However, coal development can play an equally significant role in releasing the nitrogen fixed in coal into surface watersheds in the form of nitrate, nitrite, or ammonia, consequently threatening the water quality of surface water systems in mining areas. In this study, a typical karst surface watershed system affected by coal mining activities was selected for an in-depth investigation with the aim of realistically assessing the potential contribution of coal mining to nitrogen pollution. The results reveal increasingly concerning nitrate pollution from August 2020 to November 2021 in the Huatan River watershed under the influence of anthropogenic activities, especially mining development and agricultural production. Given that the nitrogen and oxygen isotope compositions of nitrate do not support the presence of denitrification, the variation in the NO3−/Cl− ratio and the relatively stable Cl− concentration may be a reflection of nitrification. Although the leaching of atmospheric precipitation on the strata in the basin promoted the release of nitrogen associated with coal mining, the higher rate of nitrogen cycling in the oligotrophic mine water environment limited the contribution of coal mining to nitrogen pollution in the surface watershed. Specifically, the contribution of coal mining activities to nitrogen pollution in surface karst river is mainly NH4+–N, which contributes 10% or less to the nitrate input to the waters of the Huatan River. The findings thus highlight the necessity of further uncovering the geochemical cycling process of nitrogen during the transport of mine water in the coal mining environment. [ABSTRACT FROM AUTHOR]

The "2+26" cities, suffering the most severe winter haze pollution, have been the key region for air quality improvement in China. Increasing prominent nitrate pollution is one of the most challenging environmental issues in this region, necessitating development of an effective control strategy. Herein, we use observations, and state-of-the-art model simulations with scenario analysis and process analysis to quantify the effectiveness of the future SO 2 -NO X -VOC-NH 3 emission control on nitrate pollution mitigation in "2+26" cities. Focusing on a serious winter haze episode, we find that limited NO X emission reduction alone in the short-term period is a less effective choice than VOC or NH 3 emission reduction alone to decrease nitrate concentrations, due to the accelerated NO X -HNO 3 conversion by atmospheric oxidants and the enhanced HNO 3 to NO 3 − partition by ammonia, although deep NO X emission reduction is essential in the long-term period. The synergistic NH 3 and VOC emission control is strongly recommended, which can counteract the adverse effects of nonlinear photochemistry and aerosol chemical feedback to decrease nitrate more. Such extra benefits will be reduced if the synergistic NH 3 and VOC reduction is delayed, and thus reducing emission of multiple precursors is urgently required for the effective control of increasingly severe winter nitrate pollution in "2+26" cities. [ABSTRACT FROM AUTHOR]

Elevated and increasing NO3− ${{\text{NO}}_{3}}^{-}$ concentration in groundwater affect groundwater supplies in China and elsewhere. However, how groundwater flow affects NO3− ${{\text{NO}}_{3}}^{-}$ concentration in groundwater has yet to be fully understood. Herein, multi‐isotopes (15N, 11B, 18O, and 2H) and local indicators of spatial association (LISA) were used to elucidate the spatiotemporal variation, sources, and patterns of NO3− ${{\text{NO}}_{3}}^{-}$ and its response to groundwater flow in Poyang Lake Basin where agriculture, industry and urban coexist. The location of NO3− ${{\text{NO}}_{3}}^{-}$ hotspots identified by LISA tended to move from the middle to lower reaches of Ganfu Plain with groundwater flow, and hotspots area expanded in the upper reaches of Xin River Basin and northwest of the study area during the transition from dry season to wet season. Our results revealed that variations of regional NO3− ${{\text{NO}}_{3}}^{-}$ concentration were controlled by groundwater recharge or flow mode (vertical or lateral), biogeochemical processes and sources (sewage and manure). In some areas with the single stratigraphic structure (unconfined aquifer), spatiotemporal variation of NO3− ${{\text{NO}}_{3}}^{-}$ concentration was influenced by local pollution sources and vertical recharge of current precipitation (vertical flow). In some areas with binary structures (confined aquifer), groundwater was mainly recharged by lateral flow and NO3− ${{\text{NO}}_{3}}^{-}$ concentration was mainly affected by mixing effect of upstream groundwater, reflecting human activities in the upper reaches rather than local human activities. In lakeside floodplain, groundwater NO3− ${{\text{NO}}_{3}}^{-}$ was attenuated by the dissimilatory NO3− ${{\text{NO}}_{3}}^{-}$ reduction to NH4+ ${{\text{NH}}_{4}}^{+}$. This study provides a novel insight into groundwater flow controlling on spatiotemporal distribution of NO3− ${{\text{NO}}_{3}}^{-}$ concentration in the regional scale. Key Points: Regional‐seasonal changes of hotspots and cool spots of nitrate concentration were identified by local indicators of spatial associationNitrate hotspots showed a seasonal shift along flow or expansion dominated by groundwater recharge mode linked with aquifer heterogeneityWe developed a conceptual model of spatiotemporal variation in regional nitrate content that describes the crucial role of groundwater flow [ABSTRACT FROM AUTHOR]

Nitrogen (N) and phosphorus (P) play crucial roles in tea planting, but information on how the long-term excessive application of chemical N fertilizer affected N and P in subtropical tea plantations remains limited. In this study, soil and leaf samples were collected along a chronosequence of tea plantations (0-, 5-, 10-, 18- and 23-year-old plantations) with excessive N input but no P application to investigate the effects of planting age on N and P availability. Diverse soil N forms and P fractions, and the concentrations of leaf N and P were measured. The results showed that (1) N O 3 − -N and dissolved organic nitrogen (DON) concentrations in both topsoil and subsoil, and the N concentration of mature leaf showed significant upward trends with tea plantation age; (2) the concentrations of available phosphorus (AP), NaHCO3-Pi in labile P pool, NaOH-Pi and D.HCl-Pi in moderately labile P pool in both layers of soil and that the P concentration of mature leaf also increased with age; (3) the N concentration of mature leaves had closely significant logarithmic relations with N O 3 − -N concentration, while the TP (total P) concentration of mature leaves had significant positive correlations with AP; and (4) the ratio of N/P in tea leaves indicated a slightly P limitation in tea plantations. We concluded that the N O 3 − -N concentration, instead of TN (total N) of N H 4 + -N, would be a good indicator to reflect N availability for tea trees, and the increasing of N O 3 − -N concentration in soil has a diminishing promoting effect on the TN concentration of mature leaves. The long-term application of chemical N fertilizer had not lead to serious P limitation in subtropical tea plantations. Generally, our study could contribute to improving our understanding of N and P availability and optimizing fertilization management in subtropical tea plantations. [ABSTRACT FROM AUTHOR]

With the rapid development of cities in northwest China, there has been an increasing focus on groundwater pollution in plateau cities, specifically the common occurrence of nitrate pollution. The special climatic, geological, and geomorphological characteristics of plateau and river valley cities contribute to distinct groundwater chemical characteristics. Therefore, the formation and evolution process of groundwater nitrate contamination differs from that of plain cities. To explore these issues, we conducted an analysis of eight major ions in various groups of water samples obtained from rivers, springs, and groundwater in Haidong. By utilizing factor analysis and correlation analysis, we were able to identify the characteristics and formation of groundwater chemistry and nitrate pollution in Haidong. Our findings reveal that the chemical characteristics of groundwater in Haidong are primarily controlled by rock weathering, mineral dissolution, and evaporation, leading to the formation of highly mineralized groundwater. Additionally, the excessive nitrate content in certain areas is a result of domestic sewage discharge and agricultural fertilizer use, exceeding Chinese drinking water health standards. Furthermore, for cities located in valleys, the geological structure significantly impacts the nitrate content of groundwater in different regions. Areas with obstructed groundwater flow tend to have higher nitrate levels, whereas regions with unobstructed groundwater experience lower nitrate concentrations. Notably, shallow groundwater is more vulnerable to nitrate pollution compared to deep groundwater. This study holds great significance in understanding the chemical characteristics of groundwater and the formation and evolution of nitrate pollution in highland river valley cities. [ABSTRACT FROM AUTHOR]

The ecology and environment of the Yellow River Basin is threatened by fluoride and nitrate contamination induced by anthropogenic activity and geogenic factors. As a result, deciphering the spatio-temporal variability of fluoride and nitrate contamination in this area remains a challenge. Three hundred eighty-six samples of surface water and groundwater from the Inner Mongolia Reaches of the Yellow River Basin were taken for this investigation. According to the results of the multivariate statistical and geostatistical analyses, the fluoride pollution was primarily discovered in the middle and lower reaches of the study area and was determined to be more severe during the dry season. In contrast, nitrate contamination was found to be more severe during the wet season while being widely distributed in groundwater and concentrated in areas with intensive agricultural activities. The primary mechanisms governing the spatial-seasonal patterns of NO3− and F− pollution were shown by the principal component analysis, isotopic, and hydrochemical diagrams. The water-rock interaction or evaporation was crucial in the enrichment of F−. The human inputs (e.g., fertilizer or sewage) dominated fluoride and nitrate contamination. Additionally, the alkaline environment played a role in the generation of NO3− and F−. The health risk assessment concluded that the threat of fluoride contamination was greater than that of nitrate contamination. Children faced the greatest health risks, followed by females and males. These findings would serve as a guide for water management and pollution control in the Yellow River Basin. [ABSTRACT FROM AUTHOR]

Groundwater is important for human survival and development, particularly in arid and semi-arid regions. This study aimed to analyze the hydrochemical characteristics, influencing factors, and the impact of human activities on groundwater in the semi-arid plains of western Jilin Province, northwest China. The study collected 88 and 151 phreatic and confined water samples, respectively, which were analyzed for 13 water quality indicators using statistical and graphical methods. In order to investigate the impact of anthropogenic activities on water quality and health risks, the improved combined weighted water quality index (ICWQI) based on the entropy weight, criteria importance though inter-criteria correlation (CRITIC), the coefficient of difference method, subjective weight based on quality grading criteria, and the water quality index (WQI) were proposed to evaluate the water quality of the study area. Meanwhile, the human health risk assessment (HHRA) model was used to assess the risks of nitrate to the health of humans in different ages and sex categories. The results indicated that the groundwater in the study area was weakly alkaline and the main hydrochemical types in the phreatic and confined water were HCO3−·Ca–Mg and HCO3−–Na. Rock weathering was the dominant process responsible for the generation of groundwater ions, the ions in groundwater primarily originate from the dissolution of halite, gypsum, and feldspar, while dolomitization promotes an increase in Mg2+. Human activities lead to an increase in NO3− in groundwater and have an impact on water quality and human health risks. The ICWQI method was found to yield more precise and rational assessments of water quality. Groundwater quality is primarily affected by nitrate ions. The areas in which groundwater nitrate posed a higher risk to human health were found to be mainly in the saline-alkali lands of Qian'an, Tongyu, and Zhenlai. Fertilizers, pesticides, and livestock farming activities contribute to the pollution of surface water. This surface contamination then infiltrates abandoned confined wells, leading to contamination of the confined aquifers. This study can improve the understanding of groundwater hydrochemical characteristics and the impact of human activities on groundwater in the study area. This study can also contribute to the study of groundwater in semi-arid regions. [ABSTRACT FROM AUTHOR]

To evaluate the effects of application of biochar and straw return for consecutive years on N2O emissions and crop yields in North China, a three-year field experiment of applying biochar and straw following a ten-year application was conducted in a wheat–maize rotation system. Four treatments were set up, including F (NPK fertilizer only); FB (NPK fertilizer + 9.0 t·ha−1 biochar); FS (NPK fertilizer + straw); and FSB ((NPK fertilizer + 9.0 t·ha−1 biochar combined with straw). The results showed that compared with the F treatment, the FB treatment significantly reduced soil N2O emissions by 20.2%, while the FS and FSB treatments increased it by 23.7% and 41.4%, respectively. The FB treatment reduced soil N2O emissions by 15.1% in the wheat season and 23.2% in the maize season, respectively. The FS and FSB treatments increased the N2O emissions by 20.7% and 36.7% in the wheat season, respectively, and by 25.5% and 44.2% in the maize season, respectively. In the wheat season, the soil water content (SWC), NO3−-N content and pH were the main influencing factors of the soil N2O emissions. In the maize season, SWC and NO3−-N content were the main influencing factors. In addition, the FB, FS and FSB treatments increased the crop yield by 4.99%, 8.40% and 10.25% compared with the F treatment, respectively. In conclusion, consecutive application of biochar can significantly reduce N2O emissions and improve crop yield. Although FS and FSB treatments can also improve the crop yield, they are not beneficial to suppressing N2O emissions. Therefore, the successive application of biochar is an effective measure to reduce N2O emissions and maintain crop yield. [ABSTRACT FROM AUTHOR]

Accurate identification of nitrate (NO3−) sources is the premise of non-point source pollution control in watersheds. The multiple isotope techniques (δ15N-NO3−, δ18O-NO3−, δ2H-H2O, δ18O-H2O), combined with hydrochemistry characteristics, land use information, and Bayesian stable isotope mixing model (MixSIAR), were used to identify the sources and contributions of NO3− in the agricultural watershed of the upper Zihe River, China. A total of 43 groundwater (GW) and 7 surface water (SFW) samples were collected. The results showed that NO3− concentrations of 30.23% GW samples exceeded the WHO maximum permissible limit level, whereas SFW samples did not exceed the standard. The NO3− content of GW varied significantly among different land uses. The averaged GW NO3− content in livestock farms (LF) was the highest, followed by vegetable plots (VP), kiwifruit orchards (KF), croplands (CL), and woodlands (WL). Nitrification was the main transformation process of nitrogen, while denitrification was not significant. Hydrochemical analysis results combined with NO isotopes biplot showed that manure and sewage (M&S), NH4+ fertilizers (NHF), and soil organic nitrogen (SON) were the mixed sources of NO3−. The MixSIAR model summarized that M&S was the main NO3− contributor for the entire watershed, SFW, and GW. For contribution rates of sources in GW of different land use patterns, the main contributor in KF was M&S (contributing 59.00% on average), while M&S (46.70%) and SON (33.50%) contributed significantly to NO3− in CL. Combined with the traceability results and the situation that land use patterns are changing from CL to KF in this area, improving fertilization patterns and increasing manure use efficiency are necessary to reduce NO3− input. These research results will serve as a theoretical foundation for controlling NO3− pollution in the watershed and adjusting agricultural planting structures. [ABSTRACT FROM AUTHOR]

Understanding the dynamics of soil water and nitrate in response to typical agricultural crops in dryland ecosystems are crucial for assessing ecological consequences and informing land use planning. This study was conducted in the Changwu tableland, a representative area for agricultural crop cultivation in the Loess Plateau of China. Fifteen soil profiles, including grassland, farmland, and young, mature, and old apple orchards, were sampled to investigate the effects of different land uses on soil water and nitrate dynamics using a "space-for-time" substitution approach. The results showed that the soil water content and nitrate content in farmlands were comparable to those in wild grassland. However, significant differences in soil water were observed below a depth of 2 m in apple orchards, with mature and old orchards experiencing water deficits compared to grassland of 624.9 mm and 690.0 mm, respectively. Moreover, a dried soil layer formed below a depth of 5 m in these orchards. In terms of soil nitrate, the concentration in the 0–5 m depth of apple orchards was significantly higher than that in agricultural land and grassland, and it increased with the age of the orchards. However, below 5 m, the residual nitrate stock per unit depth in apple orchards decreased to levels comparable to grassland and farmland, primarily due to the inhibitory effect of the dried soil layer on downward migration and leaching processes. Furthermore, the relationship between nitrate and soil water at 0–5 m soil depths differed during the conversion from grassland to farmland and apple orchard, with positive and negative correlations observed, respectively. This indicates that water plays a key role in influencing nitrate movement, and distinct hydrological processes occur for soil water and nitrate nitrogen under different land use change conditions. In conclusion, converting grassland and farmland to apple orchards can lead to soil water decline and nitrate accumulation in the vadose zone, posing potential threats to ecosystem sustainability and security in dryland regions. Therefore, implementing appropriate water-fertilizer management practices is crucial for promoting sustainable land use in loess drylands, with potential implications for similar areas worldwide. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential nutrient that plants require and is, most of the time, limited in different terrestrial ecosystems. Forming symbioses with plants, arbuscular mycorrhizal (AM) fungi improve mineral element uptake and the net primary production of plants. Recent reports have suggested that AM fungi mediate N uptake in plants. However, there are fewer studies on the influence of AM fungi on the response of Lycium barbarum, a medicinal plant in northwest China, under different N-addition conditions. In this study, the effect of Rhizophagus irregularis, N forms (NO3− and NH4+), and N levels (1.5, 7.5, 15, 30 mM) on the performance of L. barbarum was evaluated through a pot experiment. The application of R. irregularis significantly improved L. barbarum biomass, net photosynthetic rate, and root tissue viability under adequate NO3− and NH4+ supplies, and mycorrhizal plants showed better performance under NO3− supply. AM colonization enhanced N acquisition under adequate NO3− supply and strongly induced the expression of LbAMT3-1 in L. barbarum roots. Based on these results, we propose that NO3−-dominated N supply favors mycorrhizal symbiosis to a greater extent than NH4+; this study provides a basis for maintaining beneficial AM symbiosis during nitrogen fertilizer use in arable land. [ABSTRACT FROM AUTHOR]

Water quality assessments are essential for ensuring human and ecosystem health. This study conducted a water quality assessment on a typical coastal coal-bearing graben basin. Suitability of groundwater quality of the basin for drinking and agricultural irrigation was assessed. Hazards posed to human health by groundwater nitrate were assessed using the objective combined weight water quality index, percent sodium, sodium adsorption ratio, and health risk assessment model. The results indicated groundwater of the basin to be weakly alkaline hard-fresh or hard-brackish, and mean values of pH, total dissolved solids, and total hardness of 7.6, 1464.5 mg/L, and 794.1 mg/L, respectively. The ranks of groundwater cations and anions by abundance were Ca2+>Na+>Mg2+>K+ and HCO3−>NO3−>Cl−>SO42−>F−, respectively. The main groundwater type was Cl-Ca, followed by HCO3-Ca. The results of the water quality evaluation indicated that most groundwater in the study area is of a medium quality (38%), followed by poor (33%), and extremely poor (26%). Groundwater quality gradually worsened from inland to the coast. Groundwater of the basin was generally suitable for agricultural irrigation. Groundwater nitrate posed a hazard to over 60% of the exposed population, with infants most at risk, followed by children, adult females, and adult males. [ABSTRACT FROM AUTHOR]

• The ∼100-yr pollution history of microcystin congeners (MC-LR, MC-YR and MC-RR) in Lake Taihu, China was investigated. • MC pollution in Lake Taihu continued to increase over the past hundred years, especially after 1980s. • Nutrients concentration and composition were identified the important drivers regulating sediment MCs in Lake Taihu. Understanding the history of microcystins (MCs) pollution in large lakes can help inform future lake management. We collected sediment cores from Lake Taihu to: investigate the long-term record of MCs (MC-LR, MC-YR, and MC-RR), explore the main environmental drivers of MCs, and assess their public health and ecological risks. Results showed that MCs content in all cores increased over time. The core from north Taihu had the highest MC concentrations, with an average total MCs (sum of MC-LR, MC-YR, and MC-RR = TMCs) content of (74.31±328.55) ng/g. The core from eastern Taihu showed the lowest average TMCs content of (2.91±3.95) ng/g. PCA showed that sediment MCs at the three sites were positively correlated with sediment chlorophyll- a. MC-LR and MC-YR in northern and western Taihu negatively correlated with both the sediment total organic carbon/sediment total nitrogen ratio (STOC/STN) and water nitrate (NO 3 −-N) concentration, but three MC congeners at eastern Taihu showed positive correlations with water orthophosphate (PO 4 3−-P), NO 3 −-N, and STOC/STN. Generalized additive model analysis at each site revealed that NO 3 −-N was the main TMCs driver in northern and western Taihu where phytoplankton dominated, whereas PO 4 3−-P was the main TMCs driver in eastern Taihu where macrophytes dominated. At the whole lake scale, total phosphorus (TP) and PO 4 3−-P were the most important environmental drivers influencing MCs; TP explained 47.4%, 44.2%, and 47.6% while orthophosphate explained 34.8%, 31.2%, and 34.7% of the deviance on TMCs, MC-LR, and MC-YR, respectively. NO 3 −-N also showed a strong effect on MCs variation, especially on MC-YR. Risk assessment showed that both ecological and public health risk has increased in recent years. We conclude that while control of phosphorus and nitrogen input should be a major focus for future lake management, lake zone-specific management strategies may also be important. [Display omitted] [ABSTRACT FROM AUTHOR]

We investigated variations of PM 2.5 and water-soluble inorganic ions chemical characteristics at nine urban and rural sites in China using ground-based observations. From 2015 to 2019, mean PM 2.5 concentration across all sites decreased by 41.9 µg/m3 with a decline of 46% at urban sites and 28% at rural sites, where secondary inorganic aerosol (SIAs) contributed to 21% (urban sites) and 17% (rural sites) of the decreased PM 2.5. SIAs concentrations underwent a decline at urban locations, while sulfate (SO 4 2–), nitrate (NO 3 –), and ammonium (NH 4 +) decreased by 49.5%, 31.3% and 31.6%, respectively. However, only SO 4 2– decreased at rural sites, NO 3 – increased by 21% and NH 4 + decreased slightly. Those changes contributed to an overall SIAs increase in 2019. Higher molar ratios of NO 3 – to SO 4 2– and NH 4 + to SO 4 2– were observed at urban sites than rural sites, being highest in the heavily polluted days. Mean molar ratios of NH 3 /NH x were higher in 2019 than 2015 at both urban and rural sites, implying increasing NH x remained as free NH 3. Our observations indicated a slower transition from sulfate-driven to nitrate-driven aerosol pollution and less efficient control of NO x than SO 2 related aerosol formation in rural regions than urban regions. Moreover, the common factor at urban and rural sites appears to be a combination of lower SO 4 2– levels and an increasing fraction of NO 3 – to PM 2.5 under NH 4 +-rich conditions. Our findings imply that synchronous reduction in NO x and NH 3 emissions especially rural areas would be effective to mitigate NO 3 –-driven aerosol pollution. [Display omitted] [ABSTRACT FROM AUTHOR]

Purpose: Ammonium and nitrate are the main components of anthropogenic nitrogen (N) from atmosphere, while their ratio varies worldwide. However, it remains unclear whether forest soil ecosystem changes differ when various ratios of mixed N are added. Methods: Ammonium and nitrate were mixed in different ratios (3:7, 4:6, 5:5, 6:4, and 7:3) and forest soils were fertilized for four years. Then, the soil pH, microbial biomass, enzymatic activities, and organic carbon (SOC) were determined. The potential mechanism was analyzed using structural equation modeling. Results: Ammonium addition induced a greater fungal biomass decrease than nitrate addition (-0.618 vs. -0.329). The fungal biomass decrease further led to a decline in degradation enzymes, which resulted in SOC accumulation. Phosphatase activity increased and correlated with C-degrading enzymatic activities after N addition, indicating that phosphorous may become the limiting factor that controls degradation. Both ammonium and nitrate addition caused soil acidification (P < 0.05), but the acidification did not affect the enzymatic activities (P > 0.05). Moreover, when the added mixed N component ratios were closer to the ambient N component ratios, fewer changes in soil microbial biomass, enzymatic activities, and SOC were observed. This can be explained by the home-field advantage, because soil microbes may have adapted more readily to the ambient N components of the sample site and display fewer responses when the added N is nearly similar to the ambient N types. Conclusion: When designing N addition field experiments, the type of N compounds should be considered, besides the amount and duration. [ABSTRACT FROM AUTHOR]

The assessment of nitrogen cycle processes in paleomarine and paleolake systems commonly relies solely on total nitrogen isotopes. If organic nitrogen and adsorbed nitrate can be effectively extracted from samples, the application of nitrogen isotopic systematics in different N forms would be beneficial for reconstructing the nitrogen cycle process in pore water and would mutually complement water chemistry information. According to the variations in δ13Corg, δ15NTN, δ15Norg and δ15Nnitrate data of the Cretaceous Nenjiang Formation in the Songliao Basin, NE China, the profile could be divided into three intervals (intervals A–C). We attribute the anomalously high δ15Nnitrate (∼+20‰) from intervals A and C to the effect of sedimentary denitrification that occurred in the benthic sediments during the early diagenetic stage. We also recognize the intimate relationship between δ15Nnitrate and δ15Norg values, which are interpreted to reflect the effect of water column denitrification in the bottom waters and/or surface pore water. Based on the comparison of nitrogen isotope variability and the evolving environmental context, we interpret the water column denitrification as primarily reflecting anoxic bottom water or surface pore waters, while the sedimentary denitrification indicated by abnormally high δ15Nnitrate can effectively represent oxic bottom water. This study not only reveals that the adsorbed nitrate can be well extracted from mudstones with low thermal decomposition degrees but also suggests that the organic nitrogen‐nitrate isotope proxies can be used as a potential parameter to track the redox structure in water masses. Key Points: Abnormally high nitrate nitrogen isotopes imply massive sedimentary denitrificationSimilar organic nitrogen isotope and nitrate nitrogen isotope distributions suggest water denitrificationOrganic nitrogen isotope and nitrate nitrogen isotope proxies provide independent evidence for redox structure [ABSTRACT FROM AUTHOR]

Hydrochemical research and identification of nitrate contamination are of great significant for the endorheic basin, and the Northern Huangqihai Basin (a typical endorheic basin) was comprehensively researched. The results showed that the main hydrochemical facies were HCO3–Mg·Ca and HCO3–Ca·Mg. Spatial variation coefficients of most indices were greater than 60%, which was probably caused by human activities. The hydrochemical evolution was mainly affected by rock weathering and also by cation exchange. The D–18O relationship of groundwater was δD = 5.93δ18O − 19.18, and the d–excess range was −1.60–+6.01‰, indicating that groundwater was mainly derived from precipitation and that contaminants were very likely to enter groundwater along with precipitation infiltration. The NO3(N) contents in groundwater exceeded the standard. Hydrochemical analyses indicated that precipitation, industrial activities and synthetic NO3 were unlikely to be the main sources of nitrate contamination in the study area. No obvious denitrification occurred in the transformation process of nitrate. The δ15N(NO3) values ranged from +0.29‰ to +14.39‰, and the δ18O(NO3) values ranged from −6.47‰ to +1.24‰. Based on the δ15N(NO3) – δ18O(NO3) dual isotope technique and hydrochemical methods, manure, sewage and NH4 fertilizers were identified to be the main sources of nitrate contamination. This study highlights the effectiveness of the integration of hydrochemical and isotopic data for nitrate source identification, and is significant for fully understanding groundwater hydrochemistry in endorheic basins and scientifically managing and protecting groundwater. [ABSTRACT FROM AUTHOR]

Antibiotic resistance is a growing environmental issue. As a sink for antibiotic resistance genes (ARGs), lake surface sediments are well known for the spread of ARGs. However, the distribution pattern of ARGs and their relationship with environmental factors in vertical sediment layers are unclear. In this study, we investigated the resistome distribution in sediment cores from Taihu Lake using metagenomic analysis. The results showed that the abundance of total ARGs increased by 153% as the sediment depth rose from 0 to 50 cm, and the ARG Shannon index significantly increased. Among all the ARG types, efflux pump genes (e.g., mexT and mexW) were dominant, especially in 40-50 cm sediment. The variation in ARG with depth described above was related to the changes in bacterial adaptation to environmental gradients. Specifically, sulfate and nitrate concentrations decreased with depth, and random forest analysis showed that they were the main factors affecting the changes in ARG abundance. Environmental factors were also found to indirectly impact the distribution of ARGs by affecting the bacterial community. Potential sulfate-reducing gene/nitrate-reducing gene-ARG co-hosts were annotated through metagenomic assembly. The dominant co-hosts, Curvibacter, and Comamonas, which were enriched in deeper sediments, may have contributed to the enrichment of ARGs in deep sediments. Overall, our findings demonstrated that bacterial-mediated sulfate and nitrate reduction was closely related to sediment resistance, which provided new insights into the control of antibiotic resistance., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Understanding how plants adjust their requirements for different N forms can help elucidate plant coexistence strategies in N‐limited desert ecosystems. To understand the mechanisms involved, we investigated whether two desert herbs can directly absorb dissolved organic nitrogen (N) and tested whether the patterns changed over different growth stages.Two dominant herbaceous species, Astragalus arpilobus and Arnebia decumbens, from the southern edge of the Gurbantunggut desert, China, were selected. Short‐term (24 h) 15N‐labelled tracer (15N‐NO3, 15N‐NH4, 2‐13C‐15N‐Glycine) treatments were conducted at two soil depths (0–5 cm and 5–15 cm) in the season of rapid growth (June) and in the peak biomass season (July). Enrichment in 13C and 15N was assessed in the two species receiving glycine.The ratio 13C:15N was 0.21–1.39 at the 24‐h harvest, suggesting that approximately 10.5–69.5% of glycine had been absorbed. The amount of absorbed 15N was significantly affected by species, month, soil depth and N form. The two species absorbed most 15N from the 0–5 cm soil layer, and the absorption rate in July was higher than that in June. The absorption of 15N‐NO3 and 15N‐NH4 was significantly higher than that of 2‐13C‐15N‐Glycine.The results indicate that these herbs could use amino acids in the N‐deficient desert ecosystem. The two co‐existing species used different forms of inorganic N for their requirements and maintained a specific preference throughout various growth stages. [ABSTRACT FROM AUTHOR]

• Residual nitrate was mainly accumulated in the 4.0–8.8 m in apple orchards of CLP. • Nitrate accumulation varied with mean annual precipitation and stand age. • Mean annual precipitation (MAP) and N fertilizer application amounts dominated nitrate accumulation in the soil. • Deep soil desiccation hinders residual nitrate leaching to groundwater. Massive use of N fertilizer in apple orchards aids China's Loess Plateau (CLP) to become the largest region of apple production in the world, but it also leads to substantial nitrate accumulation in the vadose zone, posing a potential environmental risk. However, a holistic understanding of the spatial patterns and controls of soil nitrate in the vadose zone of apple orchards remains understudied, which is unfavorable for the formulation of a science-based N application strategy. To this end, we collected a total of 2852 paired data across apple orchards on the CLP from 52 published literature and 1000 paired data from our field sampling. We found that residual nitrate accumulation primarily occurred in the top 4–8.8 m soil layer, and it varied according to mean annual precipitation (MAP) and stand age; the accumulation peaked in sites with MAP of 500–600 mm and declined with a decrease in MAP; and among various stand ages, the highest nitrate content was observed in the 25-yr-old orchard. It was found that MAP and N fertilizer application amounts dominated nitrate accumulation in the soil. Furthermore, the desiccation index of the soil layer below the maximum cumulative depth was identified as the main factor influencing soil nitrate maximum accumulation depth. This means that deep soil desiccation hinders nitrate leaching towards deeper layers and reduces the risk of groundwater contamination. The findings here may provide insights into sustainable nitrogen and water management in apple orchards on the CLP and potentially in other similar regions. [ABSTRACT FROM AUTHOR]

• The denitrification rate of Lake Taihu decreased by 92 % with nitrate decreased by 71 % in 16 years. • The amount of nitrogen removed via denitrification decreased with improved water quality. • Further decline in N concentration relies on external N load reduction heavily. • Warming in winter is conducive to N-limitation in spring and summer in the lake. Nitrogen (N) concentrations in many lakes have decreased substantially in recent years due to external load reduction to mitigate harmful algal blooms. However, little attention has been paid to the linkage between the lakes' nitrogen removal efficiency and improved water quality in lakes, especially the variation of denitrification rate (DNR) under decreasing N concentrations. To understand the efficiency of N removal under improving water quality and its influence on the N control targets in Lake Taihu, a denitrification model based on in situ experimental results was developed and long-term (from 2007 to 2022) water quality and meteorological observations were used to estimate DNR and relate it to the amount of N removal (ANR) from the lake. The concentration of total nitrogen (TN) in Lake Taihu decreased from 3.28 mg L−1 to 1.41 mg L−1 from 2007 to 2022 but the reduction showed spatial heterogeneity. The annual mean DNR decreased from 45.6 μmol m−2 h−1 to 4.2 μmol m−2 h−1, and ANR decreased from 11.85×103 t yr−1 to 1.17×103 t yr−1 during the study years. N budget analysis suggested that the amount of N removed by denitrification accounted for 23.3 % of the external load in 2007, but decreased to only 4.0 % in 2022. Thus, the contribution of N removal by internal N cycling decreased significantly as water quality improved. Notably, the proportion of ANR in winter to total ANR increased from 14 % in 2007 to 23 % in 2022 due to warming. This could potentially lead to N deficiencies in spring and summer, thus limiting the availability of N to phytoplankton. A TN concentration of less than 1.0 mg L−1 in the lake and 1.5 mg L−1 in the inflowing lake zones in spring contribute to local N-limitation in Lake Taihu for cyanobacteria control. Our study revealed a general pattern that N removal efficiency decreases with improved water quality, which is instructive for eutrophic lakes in nitrogen management. The conceptual diagram illustrates the decreased N removal efficiency during the lake restoration process, increasing the reduction pressure of external nitrogen loads. [Display omitted] [ABSTRACT FROM AUTHOR]

Accurate assessment of groundwater vulnerability objectively reflects an area's potential for groundwater pollution and provides a reference basis for pollution control and prevention. The main objective of this study was to modify the original DRASTIC model to improve the consistency of groundwater vulnerability assessment results with regard to the actual conditions of the study area. To optimize the assessment objectivity, two additional factors that are influenced by human activities (land use and degree of groundwater extraction) were added to form the DRASTICLE model. Then, based on the correlation between all factors and measured nitrate concentrations, the improved three-scale analytic hierarchy process (AHP) and the weights of evidence (WOE) methods were used to reassign the factor weights of the DRASTICLE model. The area under the receiver operating characteristic (ROC) curve, denoted as AUC, was used to quantitatively evaluate the accuracy of all four models (original DRASTIC model AUC: 0.62). By modifying the factors and weights, the three new models showed better performance, AUC values were 0.64, 0.73 and 0.85 for the DRASTICLE, AHP-DRASTICLE, and WOE-DRASTICLE models, respectively. These results indicate that the modified models could more accurately convey groundwater vulnerability in the study area. The WOE-DRASTICLE model, which had the best performance, was then used to assess groundwater vulnerability in 2000 and 2010 and these were compared to 2018. In 2000, 2010, and 2018, the proportion of areas with very high groundwater vulnerability was 5%, 6%, 8%, respectively. Meanwhile, the proportion of areas with very low vulnerability decreased from 73 to 75%, and then rose to 82%, indicating that the spatial distribution of groundwater vulnerability has changed over time. Findings of this study are expected to provide a new theoretical basis for the Baicheng City municipal government in China to better manage and exploit groundwater resources. [ABSTRACT FROM AUTHOR]

Spatiotemporal variation of nitrate (NO3 ¯ ) and isotope components were investigated in the karst and non-karst sub-basins, to clarify the influence of hydrogeological conditions and underlying surface properties on the source and migration of nitrate in water. The research areas were selected as the Mudong and the Jingui sub-basin in the Qingshitan Reservoir Irrigation District of Lijiang River Basin in southwest China. Both small karst watersheds were also dominated by agricultural activity. Multiple isotopes (δD-H2O, δ18O-H2O, δ15N-NO3 ¯, and δ18O-NO3 ¯ ) and the Bayesian Model Stable Isotope Analysis in the R (SIAR) model were applied to compare the multiple potential nitrate sources in the water. The results indicated that the spatial and temporal variation of nitrate in water depended on the hydrogeological conditions and the associated topography, soil characteristics, and land use types of the sub-basin. Total nitrogen (TN) was mainly formed by NO3 ¯ and NH4 + in the river, where the proportion of NO3‾ was slightly higher while decreasing along the river. TN was overwhelmingly dominated by NO3‾ in the shallow groundwater. Nitrification was the dominant process of NO3 ¯ formation and transformation. The Jingui sub-basin included the woodland with a thicker soil layer, while the Mudong sub-basin was mainly agricultural land with the karst development and the discontinuous thin soil layer. The ranges of mean NO3 ¯ concentration (0.19-15.84 mg/L), and the isotope values of δD-H2O (from -44.08‰ to -19.63‰), δ18O-H3O (from -7.24‰ to -1.55‰), δ15N-NO3 ¯ (from -1.65‰ to 53.98‰), and δ18O-NO3 ¯ (from 0.04‰ to 13.74‰) in the Mudong sub-basin, were all greater than those in the Jingui sub-basin. In terms of spatial distribution, the mixing of nitrogen fertilizer infiltration from the orchard of exposed karst stone mountain in the north recharge area and manure & septic waste infiltration from the village groups were not smoothly dispersed and discharged in the central tectonic basin region, resulting in the high concentration of NO3 ¯ (the mean concentration range from 11.96 to 15.84 mg/L) and the high isotope value of δ15N-NO3 ¯ (from 0.65‰ to 28.23‰) and δ18O-NO3 ¯ (from 2.46‰ to 14.43‰) in the water of G4-G7 wells. The contributions of NO3 ¯ sourced from the soil nitrogen in the dry season, as well as the manure and septic waste in the wet season in the Mudong sub-basin, were less than those in the Jingui sub-basin. The reason was the low capacity of water storage in the thin soil layer that was formed by the weathering of carbonate rocks, together with the strong permeability of the shallow soil layer in the Mudong sub-basin. Consequently, spatial and temporal variations of nitrate pollution and migration in water were achieved under karst hydrogeological conditions and underlying surface properties. The finding can provide decision support for the control of agricultural non-point source pollution and the improvement of the water environment in karst and non-karst areas. [ABSTRACT FROM AUTHOR]

China's groundwater is facing a significant threat from nitrate pollution. Here we analyzed 2348 regional surveys of groundwater nitrate levels in China from 1990 to 2020, examining distribution, trends, and drivers. This study uncovers a concerning rise in nitrate pollution, with estimated median nitrate levels climbing from 3.84 mg/L in 1990 to 6.94 mg/L in 2020. A stark contrast is observed between regions: the northern areas have a median nitrate concentration of 8.54 mg/L, significantly higher than the southern regions, where the median is just 7.15 mg/L. From 1990 to 2020, agricultural activity consistently emerges as the dominant driver of changes in groundwater nitrate concentrations, while groundwater exploitation, domestic pollution, and industrial production also contribute to varying degrees. This analysis highlights the urgency for region-specific policies and interventions to address the escalating nitrate pollution in China's groundwater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Inc. All rights reserved.)

This study used dual stable isotopes to examine nitrate sources and geographical distribution in the Liao River Basin (LRB), one of China's seven major river basins. During a normal hydrological season in April 2021, water samples were taken from the main streams of the Liao River (MLR), Shuangtaizi River (STR), Hun River (HR), Taizi River (TZR), and Daliao River (DLR). Monitoring results indicated that 93% of the water samples had a total nitrogen level exceeding the Class IV limit (1.5 mg/L) of the 'Environmental Quality Standards (EQS) for surface water', indicating a serious nitrogen pollution status. 71.3% of the total nitrogen on average was in the form of nitrate. The scatterplots of δD-H 2 O and δ 18 O-H 2 O showed that water in TZR and DLR were mainly affected by precipitation, while MLR, STR and HR were additionally impacted by evaporation and groundwater. The overall δ 15 N and δ 18 O of NO 3 - varied from 7.7‰ to 17.9‰ and 0.6‰-11.2‰, respectively. The correlations between δ 15 N-NO 3 - , along with attribution results from the Bayesian isotopic mixing model, indicated a predominant role of manure/sewage (MS) pollution in affecting river nitrate, accounting for 78% of total nitrate in MLR and 72% in DLR. A positive correlation between δ 18 O-NO 3 - , along with attribution results from the Bayesian isotopic mixing model, indicated a predominant role of manure/sewage (MS) pollution in affecting river nitrate, accounting for 78% of total nitrate in MLR and 72% in DLR. A positive correlation between δ 15 in MLR indicated the occurrence of denitrification process. Overall, attribution results showed that the primary nitrate sources varied in different river systems within such a large basin, mainly due to spatially varied land use and human activities. Tailored nitrogen management strategies should be implemented to address the main anthropogenic pressures.3 - and δ 18 O-NO 3 - in MLR indicated the occurrence of denitrification process. Overall, attribution results showed that the primary nitrate sources varied in different river systems within such a large basin, mainly due to spatially varied land use and human activities. Tailored nitrogen management strategies should be implemented to address the main anthropogenic pressures., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Inc. All rights reserved.)

Background: About 30 % of vegetables in China are produced in intensively managed greenhouses comprising flood irrigation and extreme rates of nitrogen fertilizers. Little is known about denitrification N losses. Methods: Soil denitrification rates were measured by the acetylene inhibition technique applied to anaerobically incubated soil samples. Four different greenhouse management systems were differentiated: Conventional flood irrigation and over-fertilization (CIF, 800 kg N ha−1, 460 mm); CIF plus straw incorporation (CIF+S, 889 kg N ha−1, 460 mm); Drip fertigation with reduced fertilizer application rates (DIF, 314 kg N ha−1, 190 mm); DIF plus straw incorporation (DIF+S, 403 kg N ha−1, 190 mm). Soil denitrification was measured on nine sampling dates during the growing season (Feb 2019-May 2019) for the top-/ subsoil (0 – 20/ 20- 40 cm) and on three sampling dates for deep soils (40-60/ 80-100 cm). Data was used to constrain N-input-output balances of the different vegetable production systems. Results: Rates of denitrification were at least one magnitude higher in topsoil than in sub- and deep soils. Total seasonal denitrification N losses for the 0 – 40 cm soil layer ranged from 76 (DIF) to 422 kg N ha−1 (CIF+S). Straw addition stimulated soil denitrification in top- and subsoil, but not in deep soil layers. Integrating our denitrification data (0-100 cm) with additional data on N leaching, N2O emissions, plant N uptake, and NH3 volatilization showed, that on average 50 % of added N fertilizers are lost due to denitrification. Conclusions: Denitrification is likely the dominant environmental N loss pathway in greenhouse vegetable production systems. Reducing irrigation and fertilizer application rates while incorporating straw in soils allows the reduction of accumulated nitrate. [ABSTRACT FROM AUTHOR]

Identifying and quantifying water nitrate pollution is crucial for managing aquatic environment of a bay. Dongshan Bay, a significant semi-enclosed bay in the southeastern coastal area of Fujian Province, features mangrove and coral reef ecosystems at its estuary and bay mouth, respectively. Dongshan Bay is impacted by human activities such as mariculture. We quantified and analyzed nitrate pollution status in the surface waters of Dongshan Bay by measuring physicochemical parameters, stable isotopes (δ 15 N-NO 3 - , δ 18 O-NO 3 - and δ 15 N-NH 4 + ) of the surface waters, and using statistical methods including the MixSIAR isotope mixing model. The results showed that the concentrations of chlorophyll a and dissolved inorganic nitrogen in the surface waters exhibited a noticeable gradient change, decreasing from the estuary of the Zhangjiang River to the mouth of Dongshan Bay. The maximum concentrations of chlorophyll a, NH 4 + , NO 3 - and NO 2 - in the surface waters showed significant spatial variations. According to the MixSIAR model results, nitrogen sources in the surface waters of Dongshan Bay were mainly freshwater inputs of the Zhangjiang River estuary, aquaculture wastewater, and groundwater. The freshwater input from the Zhangjiang River estuary contributed the most (25.2%), while aquaculture wastewater, groundwater and urban sewage accounted for 24.6%, 19.0%, and 15.1%, respectively. It is evident that freshwater input from the Zhangjiang River estuary is the primary source of nitrate in the surface waters of Dongshan Bay.-1 , 52.67 μmol·L -1 , 379.2 μmol·L -1 and 3.93 μmol·L -1 , respectively. The nitrogen and oxygen isotope values of NH 4 + and NO 3 - in the surface waters showed significant spatial variations. According to the MixSIAR model results, nitrogen sources in the surface waters of Dongshan Bay were mainly freshwater inputs of the Zhangjiang River estuary, aquaculture wastewater, and groundwater. The freshwater input from the Zhangjiang River estuary contributed the most (25.2%), while aquaculture wastewater, groundwater and urban sewage accounted for 24.6%, 19.0%, and 15.1%, respectively. It is evident that freshwater input from the Zhangjiang River estuary is the primary source of nitrate in the surface waters of Dongshan Bay.

Anthropogenic nitrogen (N) emissions and deposition have been increasing over past decades. However, spatiotemporal variations of N deposition levels and major sources remain unclear in many regions, which hinders making strategies of emission mitigation and evaluating effects of elevated N deposition. By investigating moss N contents and δ15N values in southwestern (SW) China in 1954–1964, 1970–1994, and 2005–2015, we reconstructed fluxes and source contributions of atmospheric ammonium (NH4+) and nitrate (NO3‐) deposition and evaluated their historical changes. For urban and non‐urban sites, averaged moss N contents did not differ between 1954–1964 and 1970–1994 (1.2%–1.3%) but increased distinctly in 2005–2015 (1.6%–2.3%), and averaged moss δ15N values decreased from +0.4‰ to +3.3‰ in 1954–1964 to −1.9‰ to −0.7‰ in 1974–1990, and to −4.8‰ to −3.6‰ in 2005–2015. Based on quantitative estimations, N deposition levels from the 1950s to the 2000s did not change in the earlier 20 years but were elevated substantially in the later 30 years. Moreover, the elevation of NH4+ deposition (by 12.2 kg‐N/ha/year at urban sites and 4.6 kg‐N/ha/year at non‐urban sties) was higher than that of NO3‐ deposition (by 6.0 and 2.9 kg‐N/ha/year, respectively) in the later 30 years. This caused a shifted dominance from NO3‐ to NH4+ in N deposition. Based on isotope source apportionments, contributions of combustion‐related NH3 sources (vehicle exhausts, coal combustion, and biomass burning) to the elevation of NH4+ deposition were two times higher than volatilization NH3 sources (wastes and fertilizers) in the later 30 years. Meanwhile, non‐fossil fuel NOx sources (biomass burning, microbial N cycles) contributed generally more than fossil fuel NOx sources (vehicle exhausts and coal combustion) to the elevation of NO3‐ deposition. These results revealed significant contributions of combustion‐related NH3 and non‐fossil fuel NOx emissions to the historical elevation of N deposition in SW China, which is useful for emission mitigation and ecological effect evaluation of atmospheric N loading. [ABSTRACT FROM AUTHOR]

Nitrate pollution in surface water has attracted global attention. In order to reveal the sources of nitrate in surface water under different land-use types in China, the concentrations of NO3--N, NH4+-N and Cl- and the characteristic values of δ15N-NO3 and δ18O-NO3 in 42 watersheds in dry and wet seasons were collected and evaluated by meta-analysis. Meta-analysis results showed that the concentrations of NO3--N（Response ratio, lnR=0.20）, NH4+-N（lnR=0.54）and Cl- （lnR=0.14）in the dry season were significantly higher than in the wet season（P<0.05）. The main source of nitrate in the wet season was nitrogen fertilizer（Relative rate, RR=0.81）, and in the dry season was manure and sewage（RR=1.04）. Meta-analysis results showed that land use type had a significant influence on the source of nitrate. Urban land was mainly affected by manure and sewage（RR=1.10）, and agricultural land was affected by nitrogen fertilizer（RR=0.77）, soil nitrogen（RR=0.86）and manure and sewage（RR=0.94）in the wet season. Agricultural urban mixed land had characteristics of both urban and agricultural land. Manure and sewage（RR=1.23）and nitrogen fertilizer（RR=0.58）were the main sources in agricultural urban mixed land in dry and wet seasons, respectively. Agricultural and forestry lands were less influenced by human activities. This study provides a direction for the traceability of nitrate sources in rivers from different land use types, and provides a scientific basis for the control of nitrate pollution in rivers crossing different land use types. [ABSTRACT FROM AUTHOR]

Elevated nitrate (NO 3 −) loadings in groundwater may cause health effects in drinking water and nutrient enrichment of aquatic ecosystems. To reveal the sources and seasonal variations of NO 3 − in the coastal groundwater of Beihai, southern China, we carried out hydrochemical and isotopic (δ15N-δ18O in NO 3 −) investigations in the summer and winter, respectively, concerning multiple-aquifer groundwater, rainwater, seawater, and surface water. The sources of the main elements present in the waters were interpreted by ionic ratios. NO 3 − sources were identified by combined use of the δ15N values and δ18O values or NO 3 −/Na+ molar ratios, with estimations of the proportional contribution by the Bayesian stable isotope mixing model. Denitrification was interpreted along the flow paths. The results show groundwater main elements are originated primarily from silicate weathering, and secondarily from anthropogenic inputs and carbonate dissolution. Its qualities are largely affected by seawater intrusion along the coastline. Because of difference in the predominant minerals within the aquifers and in scale and extent of seawater intrusion, the groundwater displays distinct ionic ratio characters. NO 3 − concentrations are up to 33.9 mg/L, with higher loadings in the plains relative to along the coastline. Soil N, domestic sewage, rainwater, chemical fertilizers, and algae are NO 3 − sources, with average proportional contributions of 0.255, 0.221, 0.207, 0.202, and 0.116, respectively. In relation to the winter, higher production of NO 3 − from nitrification of soil N- and algae-derived ammonium induced by higher temperatures in the summer accounts for increases in groundwater NO 3 − loadings. In the rural areas, elevated loadings of NO 3 − in the winter may be due to larger infiltration fractions of sewage. Seasonal variations of atmospheric NO 3 − deposition and farming may also cause the dynamics. Our results improve the understanding of sources and seasonal dynamics of NO 3 − in coastal groundwater. [Display omitted] • Soil N, sewage, rainwater, and fertilizers nearly contribute to NO3− loadings equally. • The contributions of algae are minor (mean 0.116). • Temperature-stimulated nitrification induces seasonal increases in NO3− loadings. • Farming and changes of N deposition and sewage infiltration also cause the dynamics. [ABSTRACT FROM AUTHOR]

Background and aims: Plant nitrogen (N) acquisition plays an important role in regulating plant growth and ecosystem functions. However, the seasonal variations in the relative contributions of different N sources to plant N uptake and how plants modify their N absorption preferences, especially in ectomycorrhizal forests, are not well understood. Methods: We used the in situ 15N-labeling method to quantitatively estimate the relative uptake contributions of plants for three different soil N sources (nitrate, ammonium and amino acids) and plant N acquisition preferences in an ectomycorrhizal alpine forest (a 70-year-old spruce plantation on the eastern Tibetan Plateau, China) during the growing season and the nongrowing season. Results: Across the two seasons, plants in the spruce plantation showed a greater preference for acquiring soil NH4+-N, with soil NH4+ contributing more than 50% to the total N uptake of plants (57.88% during the growing season and 52.72% during the non-growing season). Moreover, amino acids exhibited a considerable contribution to the total plant N uptake, and their contribution was significantly higher during the non-growing season (33.47%) than that during the growing season (9.86%). Accordingly, plants showed a greater preference for taking up amino acids over NO3− -N in the soil as the season changed from the growing season to the non-growing season. Conclusions: Collectively, our data demonstrate that soil inorganic N is the predominant N source for plants in alpine forests, irrespective of seasonal variations. However, soil amino acids could also be an important supplementary N source for the plant N economy, especially during the non-growing season, when inorganic N availability is constrained. Our findings also suggest that plants in ectomycorrhizal alpine forests modify their nutrient absorption preference in response to seasonal changes. [ABSTRACT FROM AUTHOR]

Nitrogen (N) is an essential plant nutrient, and plants can take up N from several sources, including via mycorrhizal fungal associations. The N uptake patterns of understory plants may vary beneath different types of overstory trees, especially through the difference in their type of mycorrhizal association (arbuscular mycorrhizal, AM; or ectomycorrhizal, ECM), because soil mycorrhizal community and N availability differ beneath AM (non-ECM) and ECM overstory trees (e.g., relatively low nitrate content beneath ECM overstory trees). To test this hypothesis, we examined six co-existing AM-symbiotic understory tree species common beneath both AM-symbiotic black locust (non-ECM) and ECM-symbiotic oak trees of dryland forests in China. We measured AM fungal community composition of roots and natural abundance stable isotopic composition of N (δ15N) in plant leaves, roots, and soils. The root mycorrhizal community composition of understory trees did not significantly differ between beneath non-ECM and ECM overstory trees, although some OTUs more frequently appeared beneath non-ECM trees. Understory trees beneath non-ECM overstory trees had similar δ15N values in leaves and soil nitrate, suggesting that they took up most of their nitrogen as nitrate. Beneath ECM overstory trees, understory trees had consistently lower leaf than root δ15N, suggesting they depended on mycorrhizal fungi for N acquisition since mycorrhizal fungi transfer isotopically light N to host plants. Additionally, leaf N concentrations in the understory trees were lower beneath ECM than the non-ECM overstory trees. Our results show that, without large differences in root mycorrhizal community, the N uptake patterns of understory trees vary between beneath different overstory trees. [ABSTRACT FROM AUTHOR]

Decentralized agriculture, improper monitoring of cultivation conditions, and leaching of contaminants into lands led to the contamination of crops with various potentially toxic elements (PTEs). However, it is essential to know more about the profile level and associated risk of these contaminants and their origin, especially in high-water content crops. This study aimed to investigate the concentration of PTEs in melons of one of Iran's southern cities and follow that health risk assessment in the target population for the first time. Results of the present study confirmed that although the mean concentration of some metals was lower than the safety standard (Cr: 4.6 ± 2 mg/kg and Pb: 7.4 ± 4 mg/kg), their nutritional value was unfavorable regarding some micronutrients (Cu: 88.8 ± 27 mg/kg and Zn: 480 ± 275 mg/kg). The highest metal concentration in cantaloupe was iron (1706.47 mg/kg, p-value<0.05), and nitrate concentration in all melon types was 2.59-524.54 mg/kg (p-value<0.05). Principal component analysis (PCA) with K-means clustering and the Positive Matrix Factorization (PMF) model have shown that contaminants in melons originated from human activities. So, excessive use of agricultural fertilizers is a possible source of nitrates in melons, which have 93 % of factor loading values. The health risk assessment also showed that melons' carcinogenic and non-carcinogenic risk using the deterministic method was lower than the permissible limit (HQ < 1, ILCR 1 in the children group for the 95th percentile. Furthermore, the level of certainty in the carcinogenesis risk for children, women, and men was estimated at 86.48 %, 64.67 %, and 61.30 %, respectively. Also, the consumption rate was determined as the most important parameter in the sensitivity analysis. As a consequence, there is a potential health risk for Iranians after the consumption of melon due to PTEs and nitrate levels that also originated from anthropogenic sources., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Nitrate pollution in groundwater has become a global concern. One of the most important issues in controlling the nitrate pollution of groundwater is to identify the pollution source quickly and accurately. In this review, we firstly summarized the isotopic background values of potential sources of nitrate pollution in groundwater in 17 provinces (cities, autonomous regions) and 29 study areas in China, which could provide the fundamental database for subsequent research. Secondly, we reviewed the research progress of nitrate isotopes combined with multiple tracers for tracing nitrate in groundwater, and discussed their applicable conditions, advantages, and disadvantages. We found that halides and microorganisms combined with nitrate isotopes could accurately trace the pollution sources of domestic sewage, excrement and agricultural activities. The combination of Δ 17 O and nitrate isotopes could effectively distinguish the source of atmospheric deposition of nitrate in groundwater. The combination of groundwater age and nitrate isotopes could further determine the time scale of nitrate pollution. In addition, we summarized the application cases and compared the characteristics of mass balance mixing model, IsoSource model, Bayesian isotope mixing model, and EMMTE model for quantitative identification of nitrate pollution in groundwater. For the complexity and concealment of groundwater pollution sources, the coupling of nitrate isotopes with other chemical and biological tracing methods, as well as the application of nitrate isotope quantitative models, are effective tools for reliably identifying groundwater nitrate sources and transformation processes.

The continuous increase of nitrate (NO 3 - ) level in rivers is a hot issue in the world. However, the driving mechanism of high NO 3 - level in large rivers is still lacking, which has limited the use of river water and increased the cost of water treatment. In this study, multiple isotopes and source resolution models are applied to identify the driving mechanism of high NO 3 - level and key processes of nitrogen cycling in the lower reaches of the Yellow River (LRYR). The major sources of NO 3 level were unreasonable sewage discharge, intensity rainfall runoff, nitrification and lack of nitrate removal capacity. To control the NO - concentration, targeted measures should be implemented to improve the capacity of sewage and wastewater treatment, increase the utilization efficiency of nitrogen fertilizer and construct ecological engineering. This study deepens the understanding of the driving mechanism of high nitrate level and provides a vital reference for nitrogen pollution control in rivers to other area of the world.3 - sources were estimated by a source resolution model in the LRYR. The proportional contributions of SAM and CF to NO 3 - in the low-flow and high-flow season were 32.5%-52.3%, 44.2%-46.2% and 36.0%-40.8%, 54.9%-56.9%, respectively. The driving mechanisms of high NO 3 - level were unreasonable sewage discharge, intensity rainfall runoff, nitrification and lack of nitrate removal capacity. To control the NO 3 - concentration, targeted measures should be implemented to improve the capacity of sewage and wastewater treatment, increase the utilization efficiency of nitrogen fertilizer and construct ecological engineering. This study deepens the understanding of the driving mechanism of high nitrate level and provides a vital reference for nitrogen pollution control in rivers to other area of the world., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Aerosol liquid water content (ALWC) plays an important role in secondary aerosol formation. In this study, a whole year field campaign was conducted at Shanxi in north Zhejiang Province during 2021. ALWC estimated by ISORROPIA-II was then investigated to explore its characteristics and relationship with secondary aerosols. ALWC exhibited a highest value in spring (66.38 µg/m 3 ), followed by winter (45.08 µg/m 3 ), summer (41.64 µg/m 3 ), and autumn (35.01 µg/m 3 ), respectively. It was supposed that the secondary inorganic aerosols (SIA) were facilitated under higher ALWC conditions (RH > 80%), while the secondary organic species tended to form under lower ALWC levels. Higher RH (> 80%) promoted the NO 3 - formation via gas-particle partitioning, while SO 4 2- was generated at a relative lower RH (> 50%). The ALWC was more sensitive to NO 3 - (R = 0.94) than SO 4 2- (R = 0.90). Thus, the self-amplifying processes between the ALWC and SIA enhanced the particle mass growth. The sensitivity of ALWC and O X (NO 2  + O 3 ) to secondary organic carbon (SOC) varied in different seasons at Shanxi, more sensitive to aqueous-phase reactions (daytime R = 0.84; nighttime R = 0.54) than photochemical oxidation (daytime R = 0.23; nighttime R = 0.41) in wintertime with a high level of O X (daytime: 130-140 µg/m 3 ; nighttime: 100-140 µg/m 3 ). The self-amplifying process of ALWC and SIA and the aqueous-phase formation of SOC will enhance aerosol formation, contributing to air pollution and reduction of visibility., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

• The isotopic compositions of the potential nitrate sources were analyzed for the DRR. • The spatiotemporal variations of nitrate sources and transformations were identified. • The first research achieving the quantification of nitrate sources in the DRR. • The nitrate dynamics were highly dependent on anthropogenic activities and climate. Nitrogen pollution is a serious environmental issue in the Danjiangkou Reservoir region (DRR), the water source of the South-to-North Water Diversion Project of China. In this research, seasonal surveys and a bi-weekly time series survey were conducted in the Qihe River Basin, one of the most densely populated agricultural basins in the DRR. Hydrochemical compositions (NO 3 − and Cl−), dual isotopes (δD-H 2 O, δ18O-H 2 O, δ15N-NO 3 −, and δ18O-NO 3 −), and a Markov Chain Monte Carlo isotope mixing model were jointly applied to unravel the sources, migrations, and transformations of the nitrate (NO 3 −) in the basin. It was revealed that the mixing between different sources was the main process controlling the isotopic compositions of the riverine NO 3 − in the upper-middle reaches. In contrast, denitrification occurred in the lower reaches. For the first time, the sources of NO 3 − were quantified at a basin scale in the DRR. Overall, the river transported 484.2 tons/year of NO 3 -N to the reservoir, of which 32.6%, 36.4%, 28.0%, and 3.0% was from soil organic nitrogen, chemical fertilizer, residential sewage and atmospheric precipitation, respectively. The NO 3 -N fluxes of the different sources were regulated by the monsoon climate and anthropogenic activities. For example, high precipitation and intense fertilization resulted in severe nonpoint source pollution. Denitrification thrived in soils and reservoirs in wet seasons. Temperature could regulate the migration, nitrification and denitrification processes. Based on the results, we suggest that the management strategies dealing with nitrogen pollution issue in the DRR should follow the specific spatiotemporal characteristics of NO 3 − sources, migration and transformation mechanisms. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Background: Nitrate is one of the most common chemical contaminants of groundwater, and it is an important unqualified factor of rural groundwater in Yantai. In order to assess the risk of exposure to drinking water nitrate for adults and juveniles, in recent years, we monitored the nitrate concentrations in rural drinking water,a model was also used to assess the human health risk of nitrate pollution in groundwater.Methods: From the year 2015 to 2018, the drinking water in rural areas of Yantai was tested according to the "Sanitary Standard for Drinking Water" (GB5749-2006). The principal component analysis was used to analyze the relationship between groundwater chemicals and nitrate. The model was used to assess human health risks of groundwater nitrate through the drinking water and skin contact.Results: A total of 2348 samples were tested during the year 2015-2018.Nitrate and total dissolved solids, total hardness, chloride are all relevant, the above indicators may come from the same source of pollution; The median nitrate content (CEXP50) was 17.8 mg / L; the risk of exposure in each group was ranked as: Juveniles > Adult female > Adult male;the median health risk (HQ50) for minors and adults exceed 1.Conclusions: The concentrations of nitrate is stable and does not change over time. The high concentration of nitrate in rural areas of Yantai may be the result of the interaction of fertilizers and geological factors. The risk of exposure to nitrate in juveniles and adults is above the limit, so it is necessary to be on the alert for the high levels of nitrate. [ABSTRACT FROM AUTHOR]

A multi-isotope approach and mixing model were combined to identify spatial and seasonal variations of sources, and their proportional contribution to nitrate in the Hutuo River alluvial-pluvial fan region. The results showed that the NO 3 − concentration was significantly higher in the Hutuo River valley plain (178.7 mg/L) region than that in the upper and central pluvial fans of the Hutuo River (82.1 mg/L and 71.0 mg/L, respectively) and in the river (17.0 mg/L). Different land use types had no significant effect on the groundwater nitrate concentration. Based on a multi-isotope approach, we confirmed that the main sources of groundwater nitrate in different land use areas were domestic sewage and manure, followed by soil nitrogen, ammonia fertilizer, nitrate fertilizer and rainwater, and there were no significant spatial or seasonal variations. Combining δ15N–NO 3 -, δ18O–NO 3 - and δ37Cl results can increase the accuracy of traceability. Nitrification could be the most important nitrogen migration and transformation process, and denitrification did not significantly affected the isotopic composition of the nitrate. The SIAR model outputs revealed that the main nitrate pollution sources in groundwater and river water were domestic sewage and manure, accounting for 55.9%–61.0% and 22.6% (dry season), 50.3%–60.4% and 34.1% (transition season), 42.7%–47.6% and 35.6% (wet season 2016) and 45.9%–46.7% and 38.4% (wet season 2017), respectively. This work suggests that the random discharge and disposal of domestic sewage and manure should be the first target for control in order to prevent further nitrate contamination of the water environment. Image 1 [ABSTRACT FROM AUTHOR]

Information about seed dormancy cycling and germination in relation to temperature and moisture conditions in the natural environment is important for the conservation and restoration of rare species, including Begonia guishanensis and Paraisometrum mileense, two sympatric perennial limestone (karst) species. Dry afterripening (DAR) and wet and dry (WD) cycles at 15/5 and 25/15°C as well as moist chilling (MC) at 15/5°C were used to mimic the natural environment at different times of the year. A field experiment was conducted to monitor seasonal changes in germination responses of the seeds. About 40–65% of B. guishanensis and 5% of P. mileense seeds were dormant at maturity. DAR at 25/15 and 15/5°C as well as MC and WD cycles at 15/5°C alleviated dormancy for B. guishanensis but not P. mileense, and WD cycles at 25/15°C induced a deeper conditional dormancy for both species. Seeds of B. guishanensis exhibited dormancy cycling in the field, with increased dormancy under natural WD cycles at relatively high temperatures during the transition from the dry to the wet season in April to May and decreased dormancy during the wet season from June to October. KNO3 mitigated the dormancy-inducing effect of both artificial and natural WD cycles at relatively high temperatures for B. guishanensis. The field experiment indicated that seeds of B. guishanensis may be able to form a persistent soil seed bank, while almost all seeds of P. mileense germinate at the beginning of the wet season in the field. [ABSTRACT FROM AUTHOR]

Baseflow has become an important source of nitrate nonpoint source pollution in many intensive agricultural watersheds. Uncertainties in baseflow nutrient load separation are caused by the effects of hydrometeorological factors on both baseflow recession and baseflow nutrient load recession. These uncertainties have not been addressed well in the existing separating algorithms, which are based on simple baseflow rate–load relationships. In the present study, a recursive tracing source algorithm (RTSA) was developed based on a nonlinear reservoir algorithm and hydrometeorology‐corrected baseflow nutrient load recession parameter. This approach was used to reduce the uncertainty of baseflow nitrate load estimation caused by variations in different load recessions under varying climate conditions. RTSA validation in a typical rainy agricultural watershed yielded Nash–Sutcliffe efficiency, root mean square error‐observation standard deviation ratio, and R2 values of 0.91, 0.30, and 0.91, respectively. The baseflow nitrate–nitrogen (N─NO3–) loads from 2003 to 2012 in the Changle River watershed of eastern China were estimated with the RTSA. The results indicated that baseflow nitrate export accounted for 62.0% of the mean total annual N─NO3– loads (18.0 kg/ha). The total baseflow N─NO3– export was highest in spring (3.6 kg/ha), followed by summer (3.2 kg/ha), winter (2.3 kg/ha), and autumn (2.1 kg/ha). The contribution of baseflow to total nitrate in the stream decreased in the order of winter (69.88%) >spring (66.59%) >autumn (60.36%) >summer (54.04%). The monthly baseflow N─NO3– loads and flow‐weighted concentrations greatly increased during the research period (Mann–Kendall test, Zs > 2.56, p <.01). Without proper countermeasures, baseflow nitrate may represent a serious long‐term risk for water surfaces in the future. [ABSTRACT FROM AUTHOR]

Excessive nitrogen (N) deposition can impact lichen diversity in forest ecosystems, and this is a particular situation in China. Here, we examined the N uptake, assimilation, and the impact of excessive N deposition on the symbiotic balance of dominant epiphytic lichens in the subtropical forests in the Mts. Shennongjia of central China. The results show that lichen species took up, assimilated and utilized more ammonium than nitrate in a species‐specific way, following the increase of N availability. The photobiont of the lichens decreased with the increase of N concentration following an initial increase, while the mycobiont response to the N addition was not apparent. Considerable variation in response to excessive N deposition exists among the lichen species. Usnea longissima could regulate its N uptake, resulting in a stable photobiont‐mycobiont ratio among N treatments. In contrast, the photobiont‐mycobiont ratio of other four lichens increased initially but decreased when N concentration exceeded a certain level, and N stress may have broken the balance between photobiont and mycobiont of these lichens. Our results suggest that most epiphytic lichens in subtropical forest of central China could uptake and assimilate more ammonium than nitrate and that the balance between photobiont and mycobiont of many epiphytic lichens might change with the increasing N deposition load, which could impact the lichen diversity of this forest ecosystem. [ABSTRACT FROM AUTHOR]

Cucumber is one of the important vegetables cultivated in facilities in China. Due to the deterioration of soil quality in facilities and the low nitrogen use efficiency of existing varieties, it is common to pursue high yield through excessive application of nitrogen fertilizer. Improving crop nitrogen use efficiency is one of the important means to reduce nitrogen fertilizer input. Previous studies have shown that NLP (NIN-like protein) transcription factor family play an important role as transcription factors in regulating plant physiological responses to external nitrogen changes. However, there are few reports on NLPs in cucumber. Here we report that CsNLP1 is a potential candidate to improve cucumber nitrogen use ability. CsNLP1 silencing lines by virus-induced gene silencing (VIGS) showed a significant decrease in the plant biomass, chlorophyll content, nitrogen uptake, total nitrogen content, activities of NR, NIR, GDH, GOGAT and GS, and expression levels of genes involved in nitrogen assimilation and signalling under different nitrogen concentrations. In addition, transfer of CsNLP1 into Arabidopsis nlp7–1 mutant found that the phenotype, nitrate (NO 3 -) content, NR activity, NIR activity, GDH activity, GOGAT activity and GS activity in transgenic lines could be restored to the wild type level after NO 3 - treatment. Further study found that CsNLP1 could regulate the expression of NO 3 - responsive genes such as AtNIR1 , AtNIA2 , AtNRT1.1 and AtGS2 in plants. Overall, our data indicated that CsNLP1 can affect plant growth, and regulate nitrate assimilation by regulating nitrogen-related genes. • Biological function of CsNLP1 remains largely unknown. • Here we report that CsNLP1 is a potential candidate to improve cucumber nitrogen use ability. • This role may be mediated through regulating nitrate assimilation and nitrogen-related genes. [ABSTRACT FROM AUTHOR]

Perchlorate, nitrate, and thiocyanate are well-known inhibitors of iodide uptake and thyroid-disrupting chemicals. Widespread human exposure to them has been identified, whereas studies on their internal exposure levels among Chinese pregnant women are scarce and factors associated with them are not well recognized. The objective of this study is to determine their levels and identify the associated factors among pregnant women (n = 1120), based on a prospective birth cohort in Wuhan, central China, using repeated urine samples of three trimesters. Urinary perchlorate, thiocyanate, and nitrate were 100% detected in the samples, and specific gravity-adjusted median concentrations of them in all the samples were 12.6 ng/mL, 367 ng/mL, and 63.7 μg/mL, respectively. Their concentrations were weakly-to-moderately correlated with each other, with Spearman correlation coefficients ranging from 0.27 to 0.54. Poor reproducibility were observed for the three analytes over the three trimesters, with intraclass correlation coefficient of 0.07, 0.19, 0.04 for perchlorate, thiocyanate, and nitrate, respectively. The women who were overweight or used tap water as drinking water had significantly higher perchlorate concentrations, while those with excessive gestational weight gain had significantly higher thiocyanate concentrations (p < 0.05). The women with a college degree or above had lower nitrate concentrations (p < 0.05). Meanwhile, the median concentration of perchlorate in urine samples collected in spring, thiocyanate in those collected in winter, and nitrate in those collected in autumn, was significantly higher compared to their median concentrations in the samples collected in other three seasons (p < 0.05), respectively. Urinary perchlorate and nitrate concentrations of pregnant women in this study were higher than the concentrations of pregnant women in other countries, while thiocyanate concentrations were lower than that of most other countries. This study suggested potential covariates for future epidemiological analyses. [Display omitted] • Perchlorate, thiocyanate, nitrate were 100% detected in urine sample analyzed. • Repeated measurements were performed during three different trimesters of pregnancy. • Their levels were associated to certain demographic factors and sampling seasons. • Women in this study had higher perchlorate and nitrate levels than other countries. [ABSTRACT FROM AUTHOR]

The fish-killing dinoflagellate Karenia mikimotoi frequently blooms in China and poses a threat to food safety and human health. To better understand harmful algal blooms (HABs) caused by K. mikimotoi and predict the risk of HABs under climate change, the combined effect of nitrate and norfloxacin (NOR) on the growth of K. mikimotoi was tested. A growth model was used to test the effects of nutrients and pollutants on the carrying capacity of the unicellular algae. The carrying capacity increased with increasing concentrations of nitrate and NOR, reaching a maximum at 62.2 μmol L -1 of nitrate and 9.03 mg L -1 of NOR. The calculated carrying capacity of K. mikimotoi in the China Sea showed a declining trend from nearshore to offshore, with a value >30 × 10 6 cells L -1 in the estuary of the Changjiang River and Hangzhou Bay. The HAB index proposed in this study as a measurement of HAB risk was constructed using the carrying capacity and relative abundance from the MaxEnt (maximum entropy) model. The index showed that HABs caused by K. mikimotoi consecutively occurred in Zhejiang and Fujian coastal waters and predicted that they will continue until 2100, regardless of the greenhouse gas emission scenario. The center of the integrated area moved northward, with a range of 120-900 km. The HAB index integrates the characteristics of the carrying capacity and suitability of habitats, and expresses the information contained in the intensive and extensive variables that affect HAB occurrence. This index is a promising predictor of HAB risk in coastal waters., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Background: Exposure to air pollutants may cause immune responses and further allergic diseases, but existing studies have mostly, if not all, focused on effects of short-term exposure to PM 2.5 on allergic diseases., Objectives: We estimated associations of long-term exposure to PM 2.5 chemical constituents with allergic disease risks and effect modification., Methods: We used the baseline of a newly established, provincially representative cohort of 51,480 participants in southwest China. The presence of allergic rhinitis, allergic asthma, urticaria, and allergic conjunctivitis was self-reported by following a formed questionnaire in face-to-face interviews. The average concentrations of PM 2.5 chemical constituents (NO 3 - , SO 4 2- , NH 4 + , organic matter [OM], and black carbon [BC]) over participants' residence were estimated using machine learning models. Logistic regression with double robust estimator and weighted quantile sum regression were used to estimate the effects of PM 2.5 chemical constituents on allergic disease risks, as well as relative importance of each PM 2.5 chemical constituent., Results: Per interquartile range increase in the concentration of all PM 2.5 chemical constituents was associated with the elevated risks for allergic asthma (OR = 1.79 [1.41-2.26]), allergic conjunctivitis (1.54 [1.19-2.00]), urticaria (1.36 [1.25-1.48]), and allergic rhinitis (1.18 [1.11-1.26]). NO 3 - contributed more to risks for allergic asthma (weight = 46.05 %), urticaria (72.29 %), and allergic conjunctivitis (47.65 %), while NH 4 + contributed more to allergic rhinitis (78.07 %). OM contributed most to the risks for allergic asthma (30.81 %) and allergic conjunctivitis (31.40 %). BC was also associated with allergic rhinitis, urticaria, and allergic conjunctivitis, only with a considerable weight for urticaria (24.59 %). Joint effects of PM 2.5 chemical constituents on risks for allergic rhinitis and urticaria were stronger in minorities and farmers than their counterparts., Conclusion: Long-term exposure to PM 2.5 chemical constituents was associated with the increased allergic disease risks, with NO 3 - and NH 4 + accounting for the largest variance of the associations. Our findings would serve as scientific evidence for developing more explicit strategies of air pollution control., Competing Interests: Declaration of competing interest The authors declare they have nothing to disclose., (Copyright © 2023 Elsevier B.V. All rights reserved.)

δ 18 O is widely used to track nitrate (NO 3 - ) formation but overlooks NO 3 radical reactions with hydrocarbons (HCs), particularly in heavily emitting hazes. This study introduces high-time resolution Δ 17 O-NO 3 - as a powerful tool to quantify NO 3 - formation during five hazes in three cities. Results show significant differences between Δ 17 O-NO 3 - and δ 18 O-NO 3 - in identifying NO 3 - formation. δ 18 O-NO 3 - results suggested N 2 O 5 hydrolysis (62.0-88.4%) as the major pathway of NO 3 - formation, while Δ 17 O-NO 3 - shows the NO 3 - formation contributions of NO 2 + OH (17.7-66.3%), NO 3 + HC (10.8-49.6%), and N 2 O 5 hydrolysis (22.9-33.3%), revealing significant NO 3 + HC contribution (41.7-56%) under severe pollution. Furthermore, NO 3 - formation varies with temperatures, NO x oxidation rate (NOR), and pollution levels. Higher NO 2 + OH contribution and lower NO 3 + HC contribution were observed at higher temperatures, except for low NOR haze where higher NO 2 + OH contributions were observed at low temperatures ( T ← 10 °C). This emphasizes the significance of NO 2 + OH in emission-dominated haze. Contributions of NO 2 + OH and NO 3 + HC relate to NOR as positive ( f P1 = 3.0*NOR 2 - 2.4*NOR + 0.8) and negative ( f P2 = -2.3*NOR 2 + 1.8*NOR) quadratic functions, respectively, with min/max values at NOR = 0.4. At mild pollution, NO 2 + OH (58.1 ± 22.2%) dominated NO 3 - formation, shifting to NO 3 + HC (35.5 ± 16.3%) during severe pollution. Additionally, high-time resolution Δ 17 O-NO 3 - reveals that morning-evening rush hours and high temperatures at noon promote the contributions of NO 3 + HC and NO 2 + OH, respectively. Our results suggested that the differences in the NO 3 - pathway are attributed to temperatures, NOR, and pollution levels. Furthermore, high-time resolution Δ 17 O-NO 3 - is vital for quantifying NO 3 + HC contribution during severe hazes.

Copyright of Hydrogeology Journal is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Nitrate (NO 3 −) pollution is a serious problem worldwide. Identification of NO 3 − sources and transformation processes in aquifers is a key step in effectively controlling and mitigating NO 3 − contamination. In this study, hydrochemical, microbial, and dual isotopic approaches were integrated to elucidate the sources and processes influencing NO 3 − contamination in the Pearl River Delta, China. The results showed a severe NO 3 − contamination, with 75% of the samples having NO 3 −-N concentrations above the WHO standard of 10 mg L−1. The δ15N NO 3 - and δ18O NO 3 - values and a multivariate statistical analysis of hydrochemical data both revealed that manure and sewage were mainly responsible for NO 3 − contamination. Biological indicators further demonstrated that, manure and sewage had greater impacts on groundwater quality during the rainy season than during the dry season. Based on the significant relationships of δ15N NO 3 - and δ18O NO 3 - with the logarithmic NO 3 − concentration (Ln(NO 3 −)), denitrification was confirmed to occur in the discharge zone during the rainy season. Proteobacteria , Bacteroidetes , and Planctomycetes were identified as the dominant phyla, and Dechloromonas , Flavobacterium , and Nitrospira were dominant among the denitrifying bacteria in groundwater. The abundance of denitrifying bacteria had significant positive correlations with δ15N NO 3 - and NO 2 −-N during the rainy season, further confirming the occurrence of denitrification during the rainy season. This study showed that dual isotope techniques combined with microbial data can be a powerful tool for identifying the sources and microbial processes affecting NO 3 − in groundwater. Moreover, the results can provide useful insights for environmental managers to verify groundwater pollution and better apply remediation solutions. Image 1 • Microbial and isotopic approaches were combined to identify the sources and transformation of NO 3 − • Manure and sewage were the main sources of NO 3 − and had a greater effect on groundwater during the rainy season. • Denitrification occurred in the discharge zone during the rainy season. • These findings can assist in controlling and mitigating groundwater NO 3 − contamination. [ABSTRACT FROM AUTHOR]