Assessment of seasonal and annual patterns in phosphorus content in a monitored catchment through a partitioning approach based on hydrometeorological data.

High amounts of phosphorus (P) in rivers come mainly from two sources: fertilizers washed off from agricultural and urban areas by runoff water (non-point sources) and urban and industrial development which are translated in P discharges from wastewater treatment plants (WWTP). This work analyses the content of P in water for nearly 40 years inquiring into the origin of the sources, based on the hypothesis of runoff generation from the detection of river streamflow increases during the P contribution episode and the previous precipitation. For this purpose, the Guadaira River, which is located in the South of Spain and has a drainage surface of 1524 km2, was selected. In this watershed agricultural land use converges with numerous human activities resulting in high pressures on water quality. We found 40% of the P contribution episodes found seem to come from the runoff generated after the heaviest rainfall events, which normally occur between November and May. The remaining 60% of the P contribution episodes were found to be linked to point sources, which become more relevant from June to September, reaching the highest concentration values (6-17 mg/L). The results highlight that the target phosphate concentration value of 0.34 mg PO4/L imposed by the national legislation for a good state following the Water Framework Directive 2000/60/EC is exceeded by 96% of the measurements during the period from 1981 to 2022. On a monthly basis, PO4 loads showed a linear relationship with river streamflow (R2 = 0.94). However, on field measurements scale, a potential relationship between both variables was found, which changed according to the improvement in the wastewater treatment and facilities for 1982-1994, 1995-2017 and 2018-2022. In these three periods, different significant decreasing trends of the P content were found, mainly marked by the setup of each individual WWTP.

Occurrence and distribution of legacy and novel brominated flame retardants in river and sediments in southwest China: A seasonal investigation.

Brominated flame retardants (BFRs) and their substitutes are prevalent in the environment, especially near industrial point sources. In non-point source pollution areas, it is crucial to investigate the seasonal pollution characteristics to identify the pollution sources. In this study, compositional profiles, seasonal variations, and ecological risks of legacy BFRs and novel BFRs (NBFRs) in the water and sediment from the Tuojiang River located in southwest China were investigated. The results indicated that ΣBFRs ranged from not detected (n.d.) to 42.0 ng/L in water and from 0.13 to 17.6 ng/g in sediment, while ΣNBFRs ranged from n.d. to 15.8 ng/L in water, and from 0.25 to 6.82 ng/g in sediment. A significant seasonal variation was observed in water and sediments with high proportions of legacy BFRs (median percentage of 68.8% and 51.3% in water and sediment) in the dry season, while NBFRs (median percentage of 53.2% and 71.6% in water and sediment) exhibited predominance in the wet season. This highlighted the importance of surface runoff and atmospheric deposition as important sources of NBFRs in aquatic environments. Moreover, there were high ratios of decabromodiphenyl ethane (DBDPE) and BDE-209 (average: 1.38 and 2.76 in dry and wet season) in sediments adjacent to the residual areas, indicating a consumption shift from legacy BFRs to NBFRs in China. It was observed that legacy BFRs showed higher ecological risks compared to NBFRs in both water and sediment environments, with BDE-209 posing low to medium risks to sediment organisms. This study provides better understanding of contamination characteristics and sources of legacy BFRs and NBFRs in non-point source pollution areas.

Assessing nonpoint source pollution risk in watersheds using a water-functioning zone approach.

A thorough understanding of the geographical and spatial attributes of nonpoint source pollution risk in watersheds is crucial for conducting nonpoint source pollutant studies and implementing effective scientific administration strategies. The inclusion of a water-related functioning zone was considered during the nonpoint source's pollution risks assessment procedure. Nevertheless, there has not been a thorough investigation into the potential risk of nonpoint sources of pollution to adequately safeguard the quality of water in watersheds having varying capacities to handle contaminants in the water. This research presents an innovative approach for assessing the risk of nonpoint sources contamination. This allows for a quantitative evaluation of the effect of discharges of pollution from a sub-catchment on the quality of water bodies nearby. The nonpoint source losses of nutrients process, as modeled by the Water and Soil Assessment Tool, had been used to assess the hazard of nonpoint source contamination in Le 'a River Watersheds. This assessment happened on both yearly and monthly scales. The findings indicated that the risk of nonpoint source contamination exhibits both seasonal and regional variations and is significantly impacted by the ability of the fluid ecosystem. Elevated nonpoint sources pollutants do not always equate to elevated pollutant dangers. On the other hand, a small amount of nutrients in the nonpoint sources does not indicate an insignificant degree of susceptibility to region risk. Furthermore, by utilizing a risk assessment method that considers the capacity of the water's environment, it is possible to identify variations in risk levels that may be overlooked when solely considering nonpoint sources contaminant losses, and fluid functioning zone. This approach allows for precise regulation of nonpoint sources of pollution administration.

Fluorescence fingerprint as an indicator to identify urban non-point sources in urban river during rainfall period.

Nowadays, the urban non-point source (NPS) pollution gradually evolved as the main contributor to urban water contamination since the point source pollution was effectively controlled. It was imperative to perform urban NPS identification in urban river to meet the requirements of precise source governance. In this study, the real-time detection about water quality parameters and fluorescence fingerprints (FFs) was performed for BX River and its outlets during rainfall period. EEM-PARAFAC and component similarity analyses discovered that the pollution encountered by BX River mainly came from road runoff and untreated municipal wastewater (UMWW) overflow. The C1 (tryptophan-like) and C3 (terrestrial humic-like) components located at Ex/Em = âˆ¼230(280)/340 and ∼275/430 nm were both detected in these two kinds of urban NPS. The C2 components of road runoff and UMWW overflow displayed remarkable differences, which located at Ex/Em = 250/385 and 245/365 nm, respectively, thus could be served as indicators for distinguishing them. During rainfall period, the outflow from rainwater outlets (RWOs) constantly showed similar FF features to road runoff, while the FFs of outflow from combined sewer outlets (CSOs) alternated between those of road runoff and UMWW overflow. The FF features of sections in BX River changed in response to the dynamic variations in FFs of the outlets, which revealed real-time pollution causes of BX River. This work not only realized the identification and differentiation of urban NPS, but also elucidated the dynamic variations of pollution characteristics throughout the entire process of "urban NPS-outlets-urban river", and demonstrated the feasibility of FF technique in quickly diagnosing the pollution causes of urban river during rainfall period, which provided important guidance for urban NPS governance.

Runoff nitrogen losses under confluence and diverging drainage systems in the sloped plot scale: A comparative study.

The drainage system is a key measure for regulating runoff nutrient losses on sloping farmlands. Confluence and diverging drainage systems are two drainage layouts representing natural water network systems and are widely distributed in sloping farmlands; however, the effects of these drainage systems on runoff nutrient losses in the sloped plots remain unclear. This study investigated the effects of different drainage systems on the characteristics of runoff nitrogen (N) losses in sloped plots using laboratory rainfall simulations. Three treatments, including bare slope (without drainage system, CK), confluence drainage system (T1), and diverging drainage system (T2), were used to compare the changes in concentrations and losses of total nitrogen (TN), dissolved nitrogen (DN), and particulate nitrogen (PN), and the DN:TN ratio in runoff under a combination of 1.8 mm min-1 rainfall intensity and three slope gradients (5°, 10°, and 15°). The results showed that the time to runoff was significantly delayed in T2 compared with that in CK and T1 across all slopes (p < 0.05). Accumulated runoff depth was considerably lower in T1 and T2 than in CK across all slopes (p < 0.05). The TN and PN concentrations in T1 were markedly lower than those in T2 on the 10° and 15° slopes (p < 0.05). The DN concentration in T1 was lowest at the 5° slope (p < 0.05). TN loss in T1 was 14.7-33.9% and 17.9-30.3% lower than those in CK and T2 across all slopes, respectively (p < 0.05). The PN loss in T1 was 56.7% and 53.3% lower than that in T2 on the 10° and 15° slopes, respectively (p < 0.05). DN loss in T1 was 39.3-72.5% lower than that in CK for all slopes (p < 0.05). DN:TN in T2 was lower than that in CK and T1 at the 10° and 15° slopes (p < 0.05). Our results confirm the effectiveness of drainage systems in reducing runoff nutrient losses in a sloped plot and demonstrate that the confluence drainage system is better at reducing N losses in runoff than diverging drainage systems.

Agricultural practices and ditch size drive microbial community assembly and mediate N- and P-transformation in multistage drainage networks of paddy fields: Insights from a large-scale irrigation district in eastern China.

Agricultural drainage ditches (ADDs) are ubiquitous and regarded as active zones for biogeochemical reactions and microbe-mediated pollutant removal. However, little is known about the microbial distribution and community assembly in ADDs. Here, a typical large-scale irrigation district, including five orders of farmland drainage systems (namely field, sublateral, head, branch, and trunk ditches that could efficiently remove excess water from paddy fields to downstream water bodies), was selected to investigate the ecological processes of microbial communities and N- and P-transformation processes in multistage ditches. We found that scale effects drove distinct environmental gradients and microbial community dissimilarities and that the five ordered ditches were grouped into three clusters (field vs. sublateral vs. head, branch, and trunk ditches). Specifically, the microbial communities in the field ditches located adjacent to the paddy fields were strongly selected by agricultural fertilization and irrigation drainage, enriching salt-tolerant microbes with high nitrification and inorganic P solubilization capabilities. In comparison, the sublateral ditches showed the highest removal performance for total nitrogen (13.28-55.80%) and total phosphorus (9.06-65.07%) during the growth of rice, which was mainly attributed to the enrichment of versatile microbiota (e.g., C39, Nitrospira, and Novosphingobium) as a result of the increased stochastic processes driven by the low redox potential. Notably, the specific gene (i.e., hzsB) for anaerobic ammonium oxidation in sublateral ditches was 1-2 orders of magnitude higher than in adjacent ditches, further contributing to N loss. As field water was discharged into the large-sized head, branch, and trunk ditches, the nutrient levels decreased sharply. At the same time, deterministic processes gained more importance (∼82%), leading to the flourishing of Synechococcus and increasing the potential risk of eutrophication. Overall, the microbial communities in multistage ADDs were co-shaped by agricultural practices and ditch size, which further governed the N and P removal performance. These results provide unique insights into microbiota assembly patterns and dynamics in multistage ADDs and important ecological knowledge for controlling agricultural non-point source pollutants by managing of small-sized ditches.

Evaluation of best management practices for mitigating harmful algal blooms risk in an agricultural lake basin using a watershed model integrated with Bayesian Network approach.

Lake eutrophication caused by nitrogen and phosphorus has led to frequent harmful algal blooms (HABs), especially under the unknown challenges of climate change, which have seriously damaged human life and property. In this study, a coupled SWAT-Bayesian Network (SWAT-BN) model framework was constructed to elucidate the mechanisms between non-point source nitrogen pollution in agricultural lake watersheds and algal activities. A typical agricultural shallow lake basin, the Taihu Basin (TB), China, was chosen in this study, aiming to investigate the effectiveness of best management practices (BMPs) in controlling HABs risks in TB. By modeling total nitrogen concentration of Taihu Lake from 2007 to 2022 with four BMPs (filter strips, grassed waterway, fertilizer application reduction and no-till agriculture), the results indicated that fertilizer application reduction proved to be the most effective BMP with 0.130 of Harmful Algal Blooms Probability Reduction (HABs-PR) when reducing 40% of fertilizer, followed by filter strips with 0.01 of HABs-PR when 4815ha of filter strips were conducted, while grassed waterway and no-till agriculture showed no significant effect on preventing HABs. Furthermore, the combined practice between 40% fertilizer application reduction and 4815ha filter strips construction showed synergistic effects with HABs-PR increasing to 0.171. Precipitation and temperature data were distorted to model scenarios of extreme events. As a result, the combined approach outperformed any single BMP in terms of robustness under extreme climates. This research provides a watershed-level perspective on HABs risks mitigation and highlights the strategies to address HABs under the influence of climate change.

A spatial optimal allocation method considering multi-attribute decision making and multiple BMPs random combination in sub-watersheds.

Best management practices (BMPs) have been extensively employed in effective watershed management for non-point source pollution. The weights of objective functions and the restrictive conditions of combined BMPs are the vital requirements for BMPs allocation. Therefore, it is more beneficial to explore that a spatial optimal allocation method considering multi-attribute decision making and multiple BMPs random combination. Here is the novel framework based on Soil and Water Assessment Tool (SWAT) and the Non-dominated Sorting Genetic Algorithm II (NSGA-Ⅱ), which considers multiple objectives in deriving watershed-scale pollution control practices by considering BMPs cost and combined reduction rates of total nitrogen (TN) and total phosphorus (TP). The framework also integrates combined Entropy Weight method (EWM) and Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to solve the weights of TN and TP, and considers the attributes of the sub-basin itself, which is more local suitability. Four categories of BMPs, tillage management, nutrient management, vegetative filter strips, and landscape management, were evaluated in the Jing River Basin (JRB) and resulted in reduction rates of 9.77%, 10.53%, 16.40%, and 14.27% averagely, respectively. BMP allocation schemes, derived from multi-objective optimization, are stratified into three financial scenarios. Low-cost scenario, costing up to 2 billion RMB, primarily targets the grain for green program in 28.81% of sub-basins. Medium-cost scenario, between 2 and 6 billion RMB, predominantly utilizes the grain for green in areas with a slope greater than 15°, accounting for 20.00% of sub-basins. High-cost scenario exceeds 6 billion RMB, mainly due to the implementation of multiple combination measures. The three configuration scenarios can provide decision-makers with a trade-off between measure costs and reduction efficiency. Overall, the innovative framework not only facilitates cost-effective implementation but provides a beneficial methodology for selecting cost-effective conservation practices in other regions.

The use of the self-organizing map (SOM) methodology to study the dissolved organic matter (DOM) in different water body types.

This study investigated the characteristics of dissolved organic matter (DOM) in two distinct water bodies, through the utilization of three-dimensional fluorescence spectroscopy coupled with self-organizing map (SOM) methodology. Specifically, this analysis concentrated on neurons 3, 14, and 17 within the SOM model, identifying notable differences in the DOM compositions of a coal subsidence water body (TX) and the MaChang Reservoir (MC). The humic substance content of DOM TX exceeded that of MC. The origin of DOM in TX was primarily linked to agricultural inputs and rainfall runoff, whereas the DOM in MC was associated with human activities, displaying distinctive autochthonous features and heightened biological activity. Principal component analysis revealed that humic substances dominated the DOM in TX, while the natural DOM in MC was primarily autochthonous. Furthermore, a multiple linear regression model (MLR) determined that external pollution was responsible for 99.11% of variation in the humification index (HIX) of water bodies.

Identification of agricultural surface source pollution in plain river network areas based on 3D-EEMs and convolutional neural networks.

Agricultural non-point sources, as major sources of organic pollution, continue to flow into the river network area of the Jiangnan Plain, posing a serious threat to the quality of water bodies, the ecological environment, and human health. Therefore, there is an urgent need for a method that can accurately identify various types of agricultural organic pollution to prevent the water ecosystems in the region from significant organic pollution. In this study, a network model called RA-GoogLeNet is proposed for accurately identifying agricultural organic pollution in the river network area of the Jiangnan Plain. RA-GoogLeNet uses fluorescence spectral data of agricultural non-point source water quality in Changzhou Changdang Lake Basin, based on GoogLeNet architecture, and adds an efficient channel attention (ECA) mechanism to its A-Inception module, which enables the model to automatically learn the importance of independent channel features. ResNet are used to connect each A-Reception module. The experimental results show that RA-GoogLeNet performs well in fluorescence spectral classification of water quality, with an accuracy of 96.3%, which is 1.2% higher than the baseline model, and has good recall and F1 score. This study provides powerful technical support for the traceability of agricultural organic pollution.

Spatio-temporal characteristics and multi-scale risk identification of pollution load based on sensitivity analysis in small watersheds located in Tuojiang River Basin, China.

High-quality development of water resources supports high-quality socio-economic development. High-quality development connects high-quality life, and clarifying the key management contents of small watersheds plays an important role in building ecologically clean small watersheds and promoting regional production and life. Previous research on pollution loads has focused on examining the impact of various external drivers on pollution loads but still lacks research on the impact of changes in pollution sources themselves on pollution loads. In this study, sensitivity analysis was used to determine the impact of changes from different sources on the total pollution loads, which can recognize the critical pollution sources. We first employed the pollutant discharge coefficient method to quantify non-point source pollution loads in the small watershed in the upstream Tuojiang River basin from 2010 to 2021. Then, combination sensitivity analysis with Getis-Ord Gi* was used to identify the critical sources and their crucial areas at the global, districts (counties), and towns (streets) scales, respectively. The results indicate: (1) The pollution loads of COD, NH3-N, TN, and TP all show a decreasing trend, reducing by 18.3%, 16.2%, 18.6%, and 28.1% from 2010 to 2021, respectively; (2) Livestock and poultry breeding pollution source is the most critical source for majority areas across watershed; (3) High-risk areas are mainly concentrated in Jingyang district and its subordinate towns (streets). There is a trend of low-pollution risk areas transitioning to high-pollution risk areas, with high-risk areas predominantly concentrated in the southeast and exhibiting a noticeable phenomenon of pollution load spilling around. This study can promote other similar small watersheds, holding significant importance for non-point source pollution control in small watersheds.

Spatial distribution of pesticide use based on crop rotation data in La Plata River basin: a case study from an agricultural region of Uruguay.

The intensive global use of pesticides presents an escalating threat to human health, ecosystems, and water quality. To develop national and local environmental management strategies for mitigating pollution caused by pesticides, it is essential to understand the quantities, timing, and location of their application. This study aims to estimate the spatial distribution of pesticide use in an agricultural region of La Plata River basin in Uruguay. Estimates of pesticide use were made by surveying doses applied to each crop. This information was spatialized through identifying agricultural rotations using remote sensing techniques. The study identified the 60 major agricultural rotations in the region and mapped the use and application amount of the nine most significant active ingredients (glyphosate, 2,4-dichlorophenoxyacetic acid, flumioxazin, S-metolachlor, clethodim, flumetsulam, triflumuron, chlorantraniliprole, and fipronil). The results reveal that glyphosate is the most extensively used pesticide (53.5% of the area) and highest amount of use (> 1.44 kg/ha). Moreover, in 19% of the area, at least seven active ingredients are applied in crop rotations. This study marks the initial step in identifying rotations and estimating pesticide applications with high spatial resolution at a regional scale in agricultural regions of La Plata River basin. The results improve the understanding of pesticide spatial distribution based on data obtained from agronomists, technicians, and producers and provide a replicable methodological approach for other geographic and productive contexts. Generating baseline information is key to environmental management and decision making, towards the design of more robust monitoring systems and human exposure assessment.

Insight into the microbial nitrogen cycle in riparian soils in an agricultural region.

Riparian zones are considered as an effective measure on preventing agricultural non-point source nitrogen (N) pollution. However, the mechanism underlying microbial N removal and the characteristics of N-cycle in riparian soils remain elusive. In this study, we systematically monitored the soil potential nitrification rate (PNR), denitrification potential (DP), as well as net N2O production rate, and further used metagenomic sequencing to elucidate the mechanism underlying microbial N removal. As a whole, the riparian soil had a very strong denitrification, with the DP 3.17 times higher than the PNR and 13.82 times higher than the net N2O production rate. This was closely related to the high soil NO3--N content. In different profiles, due to the influence of extensive agricultural activities, the soil DP, PNR, and net N2O production rate near the farmland edge were relatively low. In terms of N-cycling microbial community composition, the taxa of denitrification, dissimilatory nitrate reduction, and assimilatory nitrate reduction accounted for a large proportion, all related to NO3--N reduction. The N-cycling microbial community in waterside zone showed obvious differences to the landside zone. The abundances of N-fixation and anammox genes were significantly higher in the waterside zone, while the abundances of nitrification (amoA&B&C) and urease genes were significantly higher in the landside zone. Furthermore, the groundwater table was an important biogeochemical hotspot in the waterside zone, the abundance of N-cycle genes near the groundwater table was at a relative higher level. In addition, compared to different soil depths, greater variation in N-cycling microbial community composition was observed between different profiles. These results reveal some characteristics of the soil microbial N-cycle in the riparian zone in an agricultural region and are helpful for restoration and management of the riparian zone.

Quantitative identification of nitrate and sulfate sources of a multiple land-use area impacted by mine drainage.

The rapid increase in urbanization and intensive coal mining activities have accelerated the deterioration of surface water quality. Environmental problems caused by the accumulation of nitrate and sulfate from natural, urban, and agricultural sources have attracted extensive attention. Information on nitrate and sulfate sources and their transformations is crucial for understanding the nitrogen and sulfur cycles in surface water. In this study, we monitored nitrate and sulfate in three representative rivers in mining cities in northern China. The main pollution sources and biogeochemical processes were identified by using stable isotopes (δD, δ18OH2O, δ15N, δ18ONO3, δ34S and δ18OSO4) and hydrochemistry. The contribution of natural and anthropogenic sources was quantitatively estimated based on a Bayesian mixed model. The results indicated a large variation in sulfate and nitrate sources between the different rivers. Nitrate in the Tuohe River mainly derived from manure/sewage (57.9%) and soil N (26.9%), while sulfate mainly derived from manure/sewage (41.7%) and evaporite dissolution (26.8%). For the Suihe River, nitrate was primarily sourced from chemical fertilizer (37.9%) and soil nitrogen (34.8%), while sulfate was mainly sourced from manure/sewage (33.1%) and chemical fertilizer (21.4%). For the Huihe River, nitrate mainly derived from mine drainage (56.6%) and manure/sewage (30.6%), while sulfate predominantly originated from mine drainage (58.3%) and evaporite dissolution (12.9%). Microbial nitrification was the major pathway for the migration and transformation of nitrate in the surface water. However, denitrification and bacterial sulfate reduction (BSR) did not play a significant role as aerobic conditions prevailed. In this study, we elucidated the sources and transformation mechanisms of nitrate and sulfate. Additionally, we provided a reference for formulating a comprehensive strategy for effective management and remediation of surface water contaminated with nitrate and sulfate in mining cities.

Combined effects of the earthworm casts application and fallow time on runoff and sediment loss by raindrop splashing in the Loess Plateau, China.

The importing of sources of exogenous organic carbon is an effective method for the prevention of soil degradation in sloping soils. Earthworm casts (ECs) have been recognised as a contributor to long-term carbon protection, but relatively few studies have examined the temporal impact ECs have on the achievement of this goal and its efficacy in the mitigation of soil erosion challenges in the Loess Plateau region in China. This study conducted field simulated rainfall experiments as a means of investigating the effects of five ECs (0, 200, 400, 600 and 800 g/m2, labelled CG, E1, E2, E3 and E4) on runoff, sediment and soil aggregate composition after 60, 90 and 150 days of fallow. As E4 was fallow for 150 days, the total runoff, runoff coefficient and total sediment amount decreased by 34.0%, 37.6% and 82.80% in comparison to CG. The runoff and sediment analytical models were able to accurately simulate the runoff and sediment yield processes through ECs application (R2≥0.704, RMSE≤1.108, NSE≥0.513). After being fallow for 150 days, soil sorptivity (S) increased from 0.151 cm/min0.5 to 0.310 cm/min0.5 as ECs application quantity increased. In contrast, the calibration constants of splash erosion (Cr) decreased from 0.150 to 0.090 and runoff erosion (Cf) decreased from 0.120 to 0.081. ECs were found to considerably enhance the number of aggregates that were more prominent than 0.25 mm in size. When E4 was fallow for 150 days, the fraction of >0.25 mm aggregate (WSA0.25) increased by 120.69% in comparison to CG. The mean weight diameter (MWD) grew by 105.96%, the geometric mean diameter (GMD) increased by 98.81% and the soil erodibility value K improved by 43.78%. When the amount of ECs was 800 g/m2, the stability of soil aggregates was effectively improved against water erosion while runoff and sediment transport were controlled. This can help improve the current soil and water loss situation in the Loess Plateau while also improving cultivated land soil quality. At the same time, a longer fallow period time promotes soil aggregate formation. This study is focused on the exceptional performance of ECs in limiting soil erosion on the Loess Plateau in China, which may provide novel solutions for soil and water conservation and the prevention of non-point source pollution.

Phosphorus use efficiency has crossed the turning point of the environmental kuznets curve: Opportunities and challenges for crop production in China.

The overuse of phosphate fertilizer causes waste of resources and is detrimental to the sustainability of agriculture and aquatic systems. Effective management of phosphorus (P) in agricultural systems is important. Lack of understanding on the temporal and spatial variations of P utilization in farmland systems would constrain the development of more precise and effective policies as well as management practices. Here, we used two indicators, P use efficiency (PUE) and P surplus (Psur), to evaluate changes in P utilization in crop production on both national and regional scale in China during 2005-2018. Great heterogeneity of PUE and Psur were found across different regions, with Northeast of China showing the highest PUE (0.67) and lowest Psur (11.0 kg/ha). For temporal trends, our study showed that China crossed the turning point of the environmental Kuznets curve in 2007, which indicates that China has reached a new development stage of P use that is resource-saving and environmentally friendly. Along with the processes of industrialization and urbanization in China, the development of agricultural mechanization has further resulted in an increase of PUE and decrease of Psur. Although great efforts were made, China still has a relative low PUE and high Psur compared to developed countries. Our results suggest a regionalized perspective for developing policies for the sustainable use of P resources.

A raster-based estimation of watershed phosphorus load and its impacts on surrounding rivers based on process-based modelling.

Quantifying phosphorus (P) load from watersheds at a fine scale is crucial for studying P sources in lake or river ecosystems; however, it is particularly challenging for mountain-lowland mixed watersheds. To address this challenge, we proposed a framework to estimate the P load at the grid scale and assessed its risk to surrounding rivers in a typical mountain-lowland mixed watershed (Huxi Region in Lake Taihu Basin, China). The framework coupled three models: the Phosphorus Dynamic model for lowland Polder systems (PDP), the Soil and Water Assessment Tool (SWAT), and the Export Coefficient Model (ECM). The coupled model performed satisfactory for both hydrological and water quality variables (Nash-Sutcliffe efficiency >0.5). Our modelling practice revealed that polder, non-polder, and mountainous areas had P load of 211.4, 437.2, and 149.9 t yr-1, respectively. P load intensity in lowlands and mountains was 1.75 and 0.60 kg ha-1 yr-1, respectively. A higher P load intensity (>3 kg ha-1 yr-1) was mainly observed in the non-polder area. In lowland areas, irrigated cropland, aquaculture ponds and impervious surfaces contributed 36.7%, 24.8%, and 25.8% of the P load, respectively. In mountainous areas, irrigated croplands, aquaculture ponds, and impervious surfaces contributed 28.6%, 27.0%, and 16.4% of the P load, respectively. Rivers with relatively high P load risks were mainly observed around big cities during rice season, owing to a large contribution of P load from the non-point source pollution of urban and agricultural activities. This study demonstrated a raster-based estimation of watershed P load and their impacts on surrounding rivers using coupled process-based models. It would be useful to identify the hotspots and hot moments of P load at the grid scale.

Woodchip bioreactors for saline leachates denitrification can mitigate agricultural impacts in mediterranean areas: The Campo de Cartagena-Mar Menor environmental issue.

Leachates from intensive agriculture containing high nitrate have been identified as a major cause of the severe eutrophication crisis that impacts Mar Menor (SE Spain), the largest hypersaline coastal lagoon in the Mediterranean basin. A best management practice for removing NO3--N is denitrifying bioreactors. This is the first study to assess the efficiency of citrus woodchips bioreactors in treating agricultural leachates that flow to the Mar Menor via surface discharges. Denitrification capacity, woodchip degradation (by weight loss), formation of potentially harmful compounds, and greenhouse gas (GHG) emissions were assessed. Three bioreactors (6 m × 0.98 m x 1.2 m) filled with citrus woodchips (3 m3 d-1 per bioreactor) through which the untreated ditch water over 1.5 years. Bioreactors were operated at 8 h, 16 h, and 24 h hydraulic residence time respectively, in each bioreactor. The main characteristics of the ditch water were: pH ≈ 7.5-8.0, electrical conductivity ≈ 5-8 dS m-1, dissolved organic carbon ≈6-10 mg L-1, and NO3--N ≈ 22-45 mg L-1. Bioreactors were highly efficient in reducing NO3--N. The average RNO3 in effluents was for the complete experimental period 8 g N m-3 d-1, 10.9 g N m-3 d-1, and 12.6 g N m-3 d-1 for 8, 16 and 24 h residence time, respectively. Nitrate reduction efficiency was modulated by seasonal changes in temperature, with an increasing efficiency in warmer periods (maximum ≈ 85-90% for all hydraulic residence time) and decreasing in colder ones (minimum ≈ 12%, 23% and 41% for hydraulic residence time 8, 16 and 24 h respectively). Woodchips degradation was greatest during the first six months (average ≈ 29% weight loss) in the material above the water level, attributable to aerobic mineralization of the organic carbon, while weight loss was ≈11% in woodchip media continuously below the water level. Dissolved organic carbon, sulfide, ammonium, and soluble phosphorus concentrations in the effluents were mostly low, although some peaks in concentrations occurred. Design consideration must be taken to avoid environmental impacts due to the occasional presence of harmful compounds in the effluents.

Source appointment at large-scale and ungauged catchment using physically-based model and dynamic export coefficient.

Data scarcity has caused enormous problems in non-point pollution predictions and the related source apportionment. In this study, a new framework was developed to undertake the source apportionment at a large-scale and ungauged catchment, by integrating the physically-based model and a surrogate model. The improvements were made, in terms of the application of a physically-based model in an ungauged area for the transfer process and the parametric transplantation process. The new framework was then tested in the Chaohu Lake basin, China. The result suggested that there has been a good match between simulated and observed data. Although the planting industry was the largest emission source with 48.16% of nitrogen (N), itonly contributed 12.61% of N flux to the Chaohu Lake. The ungauged catchments surrounding the Chaohu Lake were identified as non-negligible sources with 8.46% of phosphorus (P) contribution. The rainfall conditions could have great impacts on source apportionment results; e.g., the planting industry contributed from 68.17t of P in dry year to 436.02t in wet year. The new framework could be extended to other large-scale watersheds for source apportionment with data limitations.

E-commerce development and its contribution to agricultural non-point source pollution control: Evidence from 283 cities in China.

Agricultural non-point source (ANPS) pollution is a pressing environmental issue in developing countries that poses a substantial threat to sustainable development. With the rapid growth of e-commerce and its great penetration and transformation in many socioeconomic sectors, e-commerce plus agriculture is widely regarded as the solution to sustainable agricultural development. However, the environmental impacts of e-commerce on agriculture, as well as the underlying mechanisms have yet to be fully explored and verified. Based on China's practices of e-commerce development and its integration with agriculture, a panel dataset of 283 prefecture-level cities from 2009 to 2019 was collected, and a spatial difference in difference (SDID) model combined with a Durbin model was constructed to examine the local and spatial spillover effects of e-commerce development on ANPS pollution. It is found out that e-commerce development has significant positive environmental impacts achieved by stimulating industrial structure upgrading and promoting green technology innovation, while the mechanism of cultivation scaling up tends to aggravate the ANPS pollution. Spatial analysis demonstrates that e-commerce development also helps alleviate the ANPS pollution of neighboring regions with a decayed effect over a distance. Meanwhile, the impact of e-commerce on mitigating ANPS pollution shows regional heterogeneity. Those developed regions present significant positive effects, while those regions dominated by agriculture economy and without sufficient supporting facilities for e-commerce development, show significant negative effects. Therefore, we argue that the positive environmental contribution of e-commerce is not bound to happen but instead is contingent, while policies should be adapted to local conditions and enhanced to encourage the integration of e-commerce and other socioeconomic sectors, in order to develop beyond the immature pioneering stage.