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Excess nitrogen (N) discharged into streams and rivers degrades freshwater quality and threatens ecosystems worldwide. Land use patterns may influence riverine N export, yet the effect of location on N export and removal is not fully understood. We proposed a hybrid model to analyze N export and removal within the watersheds. The proposed model is satisfied for the riverine N modelling. The KGE and R 2 are 0.75 and 0.72 in the calibration period which are 0.76 and 0.61 in the validation period. Human-impacted land use may modify the N yield in the watershed, and the net N export from built-up to the in-stream system was highest in the urbanized sub-watersheds (0.81), followed by the agricultural sub-watersheds (0.88), and forested sub-watersheds (0.96). Agricultural activities make a large contribution to the N exports in the watersheds, and the mean N input from the agricultural land use to in-stream were 2069-4353 kg km -2 yr -1 . Besides, the excess inputs of N by overapplication of fertilizer and manure during the agricultural activities may increase legacy N in soil and groundwater. Biological processes for the riverine N removal may be controlled by the available substrate in the freshwater system, and temperature sensitivity of denitrification is highest in the flood seasons, especially for the human-impacted sub-watersheds. The riverine biological processes may be limited by other competitions. Our model results provide evidence that quantity and location of specific land use may control biogeochemistry within watersheds. We demonstrate the need to understand nutrient export and removal within watersheds by improving the representation of spatial patterns in existing watershed models, and we consider this study to be a new effort for the spatially explicit modeling to support land-use based N management in watersheds., 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.)

Well-defined targets for nitrogen (N) release into the local environment are essential for water management in creeks, but difficulties often arise from working with data that are too sparse to achieve reliable evaluations. Here, a simulation-optimization approach based on the QUAL2K model was developed to put forward strategies for nitrogen pollution control in a creek with sparse data in Shixi Creek, southeast China. The model showed good agreement with field observations from 22 sampling sites sampled over the period from March 2017 to February 2019, with normalized objective function (NOF) less than 0.360. Based on this model, the water pollutant sources in the creek were distinguished and analyzed. Rural sewage discharge in Shixi Creek was the major factor threatening water quality in the stream. Seasonal variations may influence the transformation of riverine N. To make more than 80% of the area in Shixi Creek meet the water quality standard of grade III, an optimized approach is to reduce more than 55% of the N pollution from point source pollution and 10% from nonpoint source pollution. This study proposed an approach that can effectively evaluate strategies for water management in a creek watershed with sparse data.

The Integrated Nitrogen CAtchments (INCA-N) model was applied to identify the sources and processes controlling riverine nitrogen (N) export in the Jiulong River watershed, coastal China. Future riverine N exports were simulated under various scenarios of climate and land-use changes. The modeling results showed good agreement between the observed and simulated values of streamflow, N concentrations, and loads. It was revealed that fertilizer application, atmospheric N deposition, and sewage discharges were the main N sources, while the primary N cycling processes included soil nitrification, soil denitrification, and N leaching. Nitrate-N exports were predominantly impacted by climate change, whereas ammonium-N exports were more affected by land-use change. The coupled effects of climate and land-use changes were projected to amplify nitrogen export by 30%, 36%, and 36% for nitrate-N and 32%, 48%, and 71% for ammonium-N during the years for 2030s, 2050s, and 2080s, respectively., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

Phytoremediation soil polluted by cadmium has drawn worldwide attention. However, how to improve the efficiency of plant remediation of cadmium contaminated soil remains unknown. Previous studies showed that nitrogen (N) significantly enhances cadmium uptake and accumulation in poplar plants. In order to explore the important role of nitrogen in plants' responses to cadmium stress, this study investigates the poplar proteome and phosphoproteome difference between Cd stress and Cd + N treatment. In total, 6573 proteins were identified, and 5838 of them were quantified. With a fold-change threshold of > 1.3, and a p -value < 0.05, 375 and 108 proteins were up- and down-regulated by Cd stress when compared to the control, respectively. Compared to the Cd stress group, 42 and 89 proteins were up- and down-regulated by Cd + N treatment, respectively. Moreover, 522 and 127 proteins were up- and down-regulated by Cd + N treatment compared to the CK group. In addition, 1471 phosphosites in 721 proteins were identified. Based on a fold-change threshold of > 1.2, and a p -value < 0.05, the Cd stress up-regulated eight proteins containing eight phosphosites, and down-regulated 58 proteins containing 69 phosphosites, whereas N + Cd treatment up-regulated 86 proteins containing 95 phosphosites, and down-regulated 17 proteins containing 17 phosphosites, when compared to Cd stress alone. N + Cd treatment up-regulated 60 proteins containing 74 phosphosites and down-regulated 37 proteins containing 42 phosphosites, when compared to the control. Several putative responses to stress proteins, as well as transcriptional and translational regulation factors, were up-regulated by the addition of exogenous nitrogen following Cd stress. Especially, heat shock protein 70 (HSP70), 14-3-3 protein, peroxidase (POD), zinc finger protein (ZFP), ABC transporter protein, eukaryotic translation initiation factor (elF) and splicing factor 3 B subunit 1-like (SF3BI) were up-regulated by Cd + N treatment at both the proteome and the phosphoproteome levels. Combing the proteomic data and phosphoproteomics data, the mechanism by which exogenous nitrogen can alleviate cadmium toxicity in poplar plants was explained at the molecular level. The results of this study will establish the solid molecular foundation of the phytoremediation method to improve cadmium-contaminated soil.

Riverine dissolved inorganic nitrogen (DIN), when elevated by human activities (e.g., land-use change), can accelerate the nitrogen cycle and downstream dispersal. However, estimating DIN export coefficients for individual land-use types can be complex due to mosaic land-use patterns and interactions between fertilizers and hydrological processes. We propose a framework that integrates an empirical model, a moving-window method, and an elasticity method to quantify seasonal DIN export coefficients for each land use in the Shixi Creek catchment, southeast China. Our model showed good agreement with field observations according to root mean square error and a normalized objective function. The export coefficients of farmland and forest were the highest (9.16 mg L−1) and lowest (2.91 mg L−1) ones, resulting in annual DIN exports, respectively, for farmland and forests of 1951 kg km−2 yr−1 and 619 kg km−2 yr−1, respectively. Urbanization was a dominant factor influencing DIN export; the export coefficient of built-up areas showed the highest elasticity and highest uncertainty, with abrupt fluctuations from dry to wet years. Our framework revealed the complex role of built-up areas in nitrogen export. Our results can shed light on how to improve riverine N management in a catchment by considering the interactive effects of climate and land use. [ABSTRACT FROM AUTHOR]

Integrated watershed management requires an analytical model capable of revealing the full range of impacts that would be caused by the uses and developments in the watershed. The SPAtially Referenced Regressions On Watershed Attributes (SPARROW) model was developed in this study to provide empirical estimates of the sources, transport of total nitrogen (TN) and total phosphorus (TP) and to develop nutrient management strategies in the Jiulong River Watershed, southeast China that has enormous influence on the region's ecological safety. We calibrated the model using data related to daily streamflow, monthly TN and TP concentrations in 2014 at 30 locations. The model produced R 2 values for TN with 0.95 and TP with 0.94. It was found that for the entire watershed, TN came from fertilizer application (43%), livestock breeding (39%) and sewage discharge (18%), while TP came from livestock breeding (46%), fertilizer application (46%), and industrial discharge (8%). Fifty-eight percent of the TN and 80% of the TP in upstream reaches are delivered to the outlets of North and West rivers. A scenario analysis with SPARROW was coupled to develop suitable management strategies. Results revealed that controlling nutrient sources was effective in improving water quality. Normally sharp reduction in nutrient sources is not operational feasible. Hence, it is recommended that preventing nutrient on land from entering into the river as a suitable strategy in watershed management. [ABSTRACT FROM AUTHOR]

Abstract: A watershed-scale approach was used to evaluate the land-based nonpoint source nutrients in the Bohai Sea Bay, which plays a vital ecological and economic role on regional scale in China. This study firstly defined the watershed boundary of the Bohai Sea Bay with an area of approximately 676,000 sq km. Loads and source apportionment of land-based nonpoint source nutrients from the 13 coastal cities, seven major watersheds, and five sub-sea areas were quantified. The land-based nonpoint source total nitrogen (TN) and total phosphorus (TP) loads from the 13 coastal cities contributed only 16.9% and 12.5% of the total land-based nonpoint source TN and TP loads entering the Bohai Sea. Land-sea integration was highlighted for managing land-based nonpoint source TN and TP loads entering the Bohai Sea. Soil losses, livestock and poultry breeding should be regulated for land-based nonpoint source TN load management while soil losses, livestock and fertilizer use should be controlled for land-based nonpoint source TP load management. Several critical source areas for land-based nonpoint source TN and TP loads were identified where management measures to reduce nutrient should be directed. The findings of this study would be helpful in gaining insights into water quality issues derived from land-based nonpoint source pollution in the BSBW from a holistic perspective, thereby providing scientific support for land-based management in the Bohai Sea. [Copyright &y& Elsevier]

The overall objective of this study is to quantify the contributions of nitrogen and phosphorus loads in surface water and identify the critical source areas in a medium-sized scale watershed in the southeast of China. The method of integrating grid-based Geographic Information Systems with empirical models is applied. The curve numbers method is used to estimate surface runoff. The Universal Soil Loss Equation is employed to predict the soil loss in the Jiulong River watershed. Empirical methods for calculating nitrogen and phosphorus discharge are further utilized to calculate loads based on the spatial analysis of a grid system. Spatial distribution of nitrogen and phosphorus loads in terms of sub-watersheds, land-use type and counties/districts in the Jiulong River watershed is represented. Various contributions and sources of nitrogen and phosphorus loads in surface water for each county or district in the Jiulong River watershed are calculated and evaluated. Study results show that excessive fertilizer use and livestock breeding contribute significant nitrogen and phosphorus loads for many counties. The contribution of livestock breeding to these nutrient loads for the Zhangzhou and Xinluo districts were 40 to 47% and 51 to 62%, respectively. Critical source areas and major contributors of non-point source nutrients are identified. The quantitative data of nutrient loads from agricultural non-point sources in the Jiulong River watershed estimated from the study could provide the scientific basis for management and control of nutrients and pollution. [ABSTRACT FROM AUTHOR]

Phytoremediation soil polluted by cadmium has drawn worldwide attention. However, how to improve the efficiency of plant remediation of cadmium contaminated soil remains unknown. Previous studies showed that nitrogen (N) significantly enhances cadmium uptake and accumulation in poplar plants. In order to explore the important role of nitrogen in plants' responses to cadmium stress, this study investigates the poplar proteome and phosphoproteome difference between Cd stress and Cd + N treatment. In total, 6573 proteins were identified, and 5838 of them were quantified. With a fold-change threshold of > 1.3, and a p-value < 0.05, 375 and 108 proteins were up- and down-regulated by Cd stress when compared to the control, respectively. Compared to the Cd stress group, 42 and 89 proteins were up- and down-regulated by Cd + N treatment, respectively. Moreover, 522 and 127 proteins were up- and down-regulated by Cd + N treatment compared to the CK group. In addition, 1471 phosphosites in 721 proteins were identified. Based on a fold-change threshold of > 1.2, and a p-value < 0.05, the Cd stress up-regulated eight proteins containing eight phosphosites, and down-regulated 58 proteins containing 69 phosphosites, whereas N + Cd treatment up-regulated 86 proteins containing 95 phosphosites, and down-regulated 17 proteins containing 17 phosphosites, when compared to Cd stress alone. N + Cd treatment up-regulated 60 proteins containing 74 phosphosites and down-regulated 37 proteins containing 42 phosphosites, when compared to the control. Several putative responses to stress proteins, as well as transcriptional and translational regulation factors, were up-regulated by the addition of exogenous nitrogen following Cd stress. Especially, heat shock protein 70 (HSP70), 14-3-3 protein, peroxidase (POD), zinc finger protein (ZFP), ABC transporter protein, eukaryotic translation initiation factor (elF) and splicing factor 3 B subunit 1-like (SF3BI) were up-regulated by Cd + N treatment at both the proteome and the phosphoproteome levels. Combing the proteomic data and phosphoproteomics data, the mechanism by which exogenous nitrogen can alleviate cadmium toxicity in poplar plants was explained at the molecular level. The results of this study will establish the solid molecular foundation of the phytoremediation method to improve cadmium-contaminated soil. [ABSTRACT FROM AUTHOR]

[Display omitted] • The DIN dynamics between the different types of sub-watersheds were identified using a spatially explicit interpretable machine learning method. • Soil moisture can strongly influence the riverine DIN concentration in the catchment, especially riverine nitrate. • Agricultural activities can increase riverine DIN with increased atmospheric NH x. Sustainable water management requires an in-depth understanding of dissolved inorganic nitrogen (DIN) in watersheds. However, it remains challenging in the context of intensifying human-induced and naturally impacted stresses in a changing environment. A spatially explicit interpretable machine-learning method was proposed based on the annual variation in land use/cover, Catchment Land Surface Model, Noah land surface model, population dynamics, and nightlight in a coastal Chinese watershed. The proposed model was effective for delineating DIN processes and sources in watersheds. The d (index of agreement), R2 (coefficient of determination), |PBIAS| (percent bias), and KGE (Kling-Gupta efficiency)during the training period were 0.91–0.98, 0.76–0.96, 0.38–3.12, and 0.73–0.87, respectively. The d, R2, |PBIAS|, and KGE during the testing period were 0.85–0.94, 0.56–0.79, 3.59–6.18, and 0.65–0.86, respectively. NH 4 +-N in the watersheds may be strongly related to the effects of urbanization within the watersheds while the agricultural activities may modify the patterns of NO 3 –-N in the watersheds. The NH 4 +-N was highly related to the urbanization effects, which contributed 20 %–30 % of the riverine NH 4 +-N in the North River. In contrast, agricultural activities may modify patterns of NO 3 –-N in watersheds, and agricultural activities in the West River contributed 50 %–70 % riverine NO 3 –-N in the watershed. Moreover, urbanization may alter the water content, soil properties, and regional climate patterns within the watersheds, while repeated DIN input through agricultural activities in the agricultural watersheds may change the nitrogen processes in the soil and groundwater. Paired with agricultural activities, dams or reservoirs may amplify NH 4 +-N to watersheds with modifying the advection and diffusion of DIN from agricultural activities, and increasing sediments in the watersheds. This study demonstrated the potentials of the proposed method in tracking DIN pollution and provided new insights into nutrient management in the watersheds under intensifying human-nature interactions. [ABSTRACT FROM AUTHOR]