Watershed Water Quality Research Articles

A Study on Paldang Reservoir Water Quality Improvement Effect by Pollutant Source Location Regulation Using Watershed-Reservoir Integrated Prediction

Objectives:Since the enactment of the 「Han-River Watershed Act」, comprehensive analysis about direct and indirect contributions and effects of various environmental policies and water quality improvement projects for the preservation of water quality in the Han-River watershed is insufficient. Especially, effect of pollutant source location regulation should be inferred and estimated through model prediction because it does not exist unregulated conditions. As development pressure in non-urban areas near the metropolitan area is increasing, it is necessary to analyze the effects of pollutant source location regulation.Methods:In this study, average pollutant density of Gangwon-do, Gyeonggi-do, and Chungcheongbuk-do, where the regulation areas located, and average pollutant density of water source management areas were compared and analyzed. After that changes in pollutant sources in regulation areas were estimated by assuming load of pollutant sources in unregulated areas that load of pollutant sources in regulation areas. Since many reservoirs are located in Han-river watershed, it is difficult to simulate the water quality of Paldang reservoir using only watershed model, BASINS/WinHSPF and EFDC-WASP were linked. Through this, change in water quality of Paldang Lake was tried to predict when the pollutant location regulation was not implemented, and to analyze the effect of the pollutant location regulation.Results and Discussion:Water quality improvement of Paldang reservoir was evaluated by applying the discharge load when the pollution source location regulation was not implemented to the calibrated model. As a result of the pollution source location regulation, discharge load in the location regulation area was analyzed to reduce by 53.90% and T-P by 48.58%, and the BOD and T-P improvement effect of Paldang Dam was analyzed 6.77% and T-P 6.62%. Since the water quality improvement effect of Paldang Lake is accumulated to the entire upstream, it is evaluated relatively less than pollutant load reducing effect.Conclusion:It was analyzed that pollutiont source location regulation has water quality improvement effect, despite the small area which only located in near Paldang reservoir compared to the total area of the Han-River watershed.

DYNAMICS OF WATER QUALITY PARAMETERS IN HYDROGRAPHIC CATCHMENTS WITH NATIVE FOREST AND PINE-PLANTED FORESTS

The search for productive forests in line with an environmental balance is one of the tasks of good sustainable forest management, in which studies on water quality in production areas support the improvement of environmental conservation programs. Thus, this study aimed to determine the water quality in watersheds covered with native forest and pine-planted forests and to evaluate the effects of forest operations and precipitation on the dynamics of physical and chemical parameters of water. Data were collected for 10 years (2005 - 2015) in a fortnightly sampling frequency. The concentrations of nitrate, phosphorus, potassium, calcium, and magnesium were determined, as well as the physical parameters of total suspended solids, pH, turbidity, apparent color, and electrical conductivity in the water. Data were analyzed using the Mann-Whitney test at 5% probability and through multivariate analysis (principal component analysis and hierarchical cluster analysis). The water quality of both watersheds is similar and there is no significant difference between the physical parameters. While the watershed composed of native forest has a higher concentration of NO 3 - , K, and Mg in the water, the watershed with planted forests of Pinus has a higher concentration of Ca. There was a chemical and physical difference in the dynamics of the water concerning its precipitation. Mosaic forest management can influence the stability of quality parameters.

Water quality assessment and pollution source apportionment using multivariate statistical techniques: a case study of the Laixi River Basin, China.

Identifying potential sources of pollution in tributaries and determining their contribution rates are critical to the treatment of water pollution in main streams. In this paper, we conducted a multivariate statistical analysis on the water quality data of 12 parameters for 3years (2018-2020) at six sampling sites in the Laixi River to qualitatively identify potential pollution sources and quantitatively calculate the contribution rates to reveal the tributaries' pollution status. Spatio-temporal cluster analysis (CA) divided 12months into two parts, corresponding to the lightly polluted season (LPS) and highly polluted season (HPS), and six sampling sites were divided into two regions, corresponding to the lightly polluted region (LPR) and highly polluted region (HPR). Principal component analysis (PCA) was used to determine the potential sources of contamination, identifying four and three potential factors in the LPS and HPS, respectively. The absolute principal component score-multiple linear regression (APCS-MLR) receptor model quantitatively analyzed the contribution rates of identified pollution sources, and the importance of the different pollution sources in LPS can be ranked as domestic sewage and industrial wastewater and breeding pollution (33.80%) > soil weathering (29.02%) > agricultural activities (20.95%) > natural influence (13.03%). HPS can be classified as agricultural cultivation (41.23%), domestic sewage and industrial wastewater and animal waste (33.19%), and natural variations (21.43%). Four potential sources were identified in LPR ranked as rural domestic sewage (31.01%) > agricultural pollution (26.82%) > industrial effluents and free-range livestock and poultry pollution (25.13%) > natural influence (14.82%). Three identified latent pollution sources in HPR were municipal sewage and industrial effluents (37.96%) > agricultural nonpoint sources and livestock and poultry wastewater (33.55%) > natural sources (25.23%). Using multivariate statistical tools to identify and quantify potential pollution sources, managers may be able to enhance water quality in tributary watersheds and develop future management plans.

Patterns and associations between dominant crop productions and water quality in an irrigated watershed

Patterns and associations between dominant crop productions and water quality in an irrigated watershed

Project-Based Unit Development by Middle School Science Teachers: Investigations on Watershed Water Quality

This case study explored changes in seven in-service middle school science teachers’ understandings of project-based learning (PBL) environments after participating in a summer institute on PBL. Of particular interest was their participation in the institute as learners in a PBL unit exploring the effect of land use on water quality in the watershed. We investigated how well teachers were able to apply their understanding of PBL as they designed their own units on water quality in their watershed. Research questions focused the study on how participation in a summer teacher institute on PBL prepared middle school teachers to describe key features of project-based learning environments, and how well they were able to incorporate these features in PBL units. Data collection included a qualitative pre/post PBL survey, teachers’ watershed units, and field notes from the institute. Findings from the pre and post survey showed that teachers demonstrated a vague understanding of essential features of PBL environments pre institute and a detailed understanding of PBL post institute. Teachers’ units varied in the degrees to which PBL features were exhibited. Strengths of the units included driving questions and benchmark lessons. Shortcomings included few opportunities for student-directed investigation of sub-driving questions.

Spatiotemporal Effect of Land Use on Water Quality in a Peri-Urban Watershed in a Brazilian Metropolitan Region: An Approach Considering GEP-Based Artificial Intelligence

The suppression of natural spaces due to urban sprawl and increases in built and agricultural environments has affected water resource quality, especially in areas with high population densities. Considering the advances in the Brazilian environmental legal framework, the present study aimed to verify whether land use has still affected water quality through a case study of a peri-urban watershed in a Brazilian metropolitan region. Analyses of physical–chemical indicators, collected at several sample points with various land-use parameters at different seasons of the year, were carried out based on an approach combining variance analysis and genetic programming. As a result, some statistically significant spatiotemporal effects on water quality associated with the land use, such as urban areas and thermotolerant coliform (R = −0.82, p < 0.01), mixed vegetation and dissolved oxygen (R = 0.80, p < 0.001), agriculture/pasture and biochemical oxygen demand (R = 0.40, p < 0.001), and sugarcane and turbidity (R = 0.65, p < 0.001), were verified. In turn, gene expression programming allowed for the computing of the importance of land-use typologies based on their capability to explain the variances of the water quality parameter. In conclusion, in spite of the advances in the Brazilian law, land use has still significantly affected water quality. Public policies and decisions are required to ensure effective compliance with legal guidelines.

Optimization of best management practices to control runoff water quality in an urban watershed using a novel framework of embedding- response surface model

Best Management Practices (BMPs) are measures implemented to reduce urban runoff volume and pollution load. Determination of a cost-effective selection of BMP combinations is a challenge. In this study, an optimization model was developed to determine the optimal number, location, and type of BMPs with minimum cost and pollution load in the Majidieh catchment in Tehran, Iran. A novel framework was proposed combining the embedding technique with Response Surface Method (RSM) called “Em-RSM” in the form of a simulation–optimization (S/O) model. First, the storm water management model)SWMM(as the simulation model was linearized, and the linear programming results were used as the initial population of the genetic algorithm (GA). Then, the linearized model along with the SWMM model were alternatively used as the fitness function in the GA evolution process to increase the model run speed and results' accuracy. The results showed that the permeable pavement and infiltration trench were more effective than other BMPs because of the physical and local characteristics of the study area. It was demonstrated that the proposed model makes a considerable reduction in the model run time with acceptable accuracy in obtaining the compromise solution of the Pareto front. The proposed framework proved its effectiveness in the solution of GA-based S/O problems. It can also be applied in other case studies or optimization problems by replacing and simplifying the behavior of the simulation model in the optimization procedure.

Scale Effects of Landscape Pattern on Water Quality in Dongjiang River Source Watershed

Based on water quality monitoring data and land use data, Dongjiang River source watershed water quality variation characteristics from 2017 to 2019 and the relationships between the landscape pattern of the Dongjiang River source watershed and water quality were analyzed using spatial analysis, correlation analysis, and redundancy analysis. The results showed that:① the water quality of the Dongjiang River source watershed improved overall, but the total nitrogen pollution was still severe. As of 2019, the annual average concentration of total nitrogen in all sampling points exceeded the type Ⅲ water quality standard. ② At the landscape level, water quality was positively correlated with landscape shape index, number of patches, and Shannon's diversity index but negatively correlated with largest patch index and aggregation index. Considering the land use type, construction land was the primary source of total nitrogen and total phosphorus. Landscape shape index and number of forest patches were positively correlated with NH4+-N. The number of forest patches was positively correlated with total phosphorus. However, the largest patch index and aggregation index of the forest were negatively correlated with total phosphorus. The number of patches of grassland was positively correlated with total phosphorus. The aggregation index of grassland was negatively correlated with total phosphorus. ③ It is suggested that management departments should focus on the optimization of the landscape pattern within the 2000 m buffer zone of monitoring points. The reasonable allocation of urban sewage-centralized treatment facilities, strengthening management of abandoned mining areas, improvement of intensive treatment of cultivated land, and construction of shelterbelt in areas where cultivated land is concentrated are beneficial for the water quality of Dongjiang River source watershed.

Evaluation of the effectiveness and effects of long-term ecological restoration on watershed water quality dynamics in two eutrophic river catchments in Lake Chaohu Basin, China

The ecological restoration projects are important in alleviating the ecological degradation conditions. The evaluation of the long-term effects and effectiveness of ecological restoration projects could provide an empirical foundation for future projects and assessment of watershed water environment restoration. However, empirical research, based upon long-term monitoring data on this topic is relatively lacking. In this study, the effectiveness of restoration projects on water quality improvement of two eutrophic rivers in Lake Chaohu Basin (LCB) was investigated. The spatiotemporal dynamics of water quality from 2000 to 2021 were studied and a delayed water quality response to restoration projects was revealed. In the past two decades, especially since 2014, the water quality in the LCB improved significantly whereas restoration projects have been implemented since late 2012. Additionally, a sharp regression discontinuity (RD) design was constructed to confirm the effectiveness of restoration projects on water quality improvement successfully. Moreover, the positive effects of restoration projects on water quality dynamics were quantified and distinguished from the effects of negative human activities and climate change using the residual trend method. During 2014–2020, ecological restoration projects contributed more than half (64.3 % SWL1 and 58.2 % HB2) of water quality variation in two eutrophic river catchments. Finally, a framework from the perspective of lake eutrophication management with effective measures is proposed for maintaining the sustainable development of ecological restoration projects in watersheds. The empirical study here provides scientific support for achieving better effectiveness of ecological restoration projects in watersheds with water pollution problems worldwide.

E-DBCM: A dynamically coupled upland and in-stream water quality model for watershed water quality simulation

A dynamic bidirectional coupled modeling framework for water environment simulation (E-DBCM), including an upland watershed model (UWSM) and a two-dimensional (2D) downstream waterbody model (DWBM), is proposed. The UWSM is implemented to describe the rainfall-runoff and determine the pollutant load to downstream waterbodies, whereas the DWBM is used to simulate the pollutant transport and flood processes on downstream waterbodies. The UWSM and DWBM are spatially connected through a moving boundary, which can ensure the mass and momentum conservation. The proposed E-DBCM is verified using three case studies and the results indicate that the E-DBCM has satisfactory numerical accuracy, which can effectively reproduce the pollutant transport process and achieve satisfactory results. The water environment in Yanqi River Basin is assessed based on the proposed model. The simulated results are consistent with the measured data, indicating that the E-DBCM is reliable and the prediction accuracy can meet the requirements of engineering practices. Water is seriously polluted in this watershed, especially during peak tourist season when many pollutants are produced. Various measures should be taken to protect the water environment in this basin.

Evaluating Impacts of Detailed Land Use and Management Inputs on the Accuracy and Resolution of SWAT Predictions in an Experimental Watershed

Land use and management practice inputs to the Soil and Water Assessment Tool (SWAT) are critical for evaluating the impact of land use change and best management practices on soil erosion and water quality in watersheds. We developed an algorithm in this study to maximize the usage of land use and management records during the setup of SWAT for a small experimental watershed in New Brunswick, Canada. In the algorithm, hydrologic response units (HRUs) were delineated based on field boundaries and associated with long-term field records. The SWAT model was further calibrated and validated with respect to water flow and sediment and nutrient (nitrate and soluble phosphorus) loadings at the watershed outlet. As a comparison, a baseline version of SWAT was also set up using the conventional way of HRU delineation with limited information on land use and management practices. These two versions of SWAT were compared with respect to input and output resolution and prediction accuracy of monthly and annual water flow and sediment and nutrient loadings. Results show that the SWAT set up with the new method had much higher accuracies in generating annual areas of crops, fertilizer application, tillage operation, flow diversion terraces (FDT), and grassed waterways in the watershed. Compared with the SWAT set up with the conventional method, the SWAT set up with the new method improved the accuracy of predicting monthly sediment loading due to a better representation of FDT in the watershed, and it also successfully estimated the spatial impact of FDT on soil erosion across the watershed. However, there was no definite increase in simulation accuracy in monthly water flow and nutrient loadings with high spatial and temporal management inputs, though monthly nutrient loading simulations were sensitive to management configuration. The annual examination also showed comparable simulation accuracy on water flow and nutrient loadings between the two models. These results indicate that SWAT, although set up with limited land use and management information, is able to provide comparable simulations of water quantity and quality at the watershed outlet, as long as the estimated land use and management practice data can reasonably represent the average land use and management condition of the watershed over the target simulation period.

ANALYSIS OF THE STATUS OF THE GIRIAN WATERSHED IN BITUNG CITY DUE TO HOUSEHOLD WASTE POLLUTION

The Girian watershed with a length of 17.5 km is the longest river in Bitung City which flows through a densely populated area as well as various industries such as smoked fish, tofu and tempeh, animal husbandry, agriculture, and industrial fish factories whose waste goes directly to the Girian watershed. The great deal of population activities can have an impact on water quality and the Girian watershed ecosystem. This study aims to analyse the water quality of the Girian watershed caused by domestic waste. This study uses a quantitative descriptive approach and the method used in this study is the Indonesian National Standard (SNI) according to the water quality parameters that have been determined. The results of the analysis of water quality upstream to downstream show that there is a decrease in water quality. Upstream is classified as good when compared to the parameters that have been determined. Densely populated areas begin to experience a decrease in water quality, namely with DO and Oil and Fat that exceeds the predetermined quality standard. As well as estuaries that have concentrations of TSS, NH3-N, Oils and Fats, COD, and BOD that exceed the specified quality standards. The results of the calculation of the pollution index show that station point 1 upstream is classified as good in 4 groups, station point 2 in densely populated areas shows lightly polluted results in group 2, and The Station 3 estuary shows moderate pollution results in group 3

A watershed water quality prediction model based on attention mechanism and Bi-LSTM.

Accurate prediction of water quality contributes to the intelligent management and control of watershed ecology. Water Quality data has time series characteristics, but the existing models only focus on the forward time series when LSTM is introduced and do not consider the effect of the reverse time series on the model. Also did not take into account the different contributions of water quality sequences to the model at different moments. In order to solve this problem, this paper proposes a watershed water quality prediction model called AT-BILSTM. The model mainly contains a Bi-LSTM layer and a temporal attention layer and introduces an attention mechanism after bidirectional feature extraction of water quality time series data to highlight the data series that have a critical impact on the prediction results. The effectiveness of the method was verified with actual datasets from four monitoring stations in Lanzhou section of the Yellow River basin in China. After comparing with the reference model, the results show that the proposed model combines the bidirectional nonlinear mapping capability of Bi-LSTM and the feature weighting feature of the attention mechanism. Taking Fuhe Bridge as an example, compared with the original LSTM model, the RMSE and MAE of the model are reduced to 0.101 and 0.059, respectively, and the R2 is improved to 0.970, which has the best prediction performance among the four cross-sections and can provide a decision basis for the comprehensive water quality management and pollutant control in the basin.

The impact of agricultural waste on river water quality of kreo watershed in Semarang city

Agricultural waste, especially from the use of fertilizers and pesticides, has become a serious problem in several countries because it has caused a decrease in river water quality. The land use and livelihoods of the people in the Kreo watershed are oriented towards agricultural activities. This study aims to (1) analyze the pattern of agricultural land use in the Kreo watershed and (2) analyze the impact of agricultural waste on river water quality in the Kreo watershed. The method used is descriptive quantitative. Analysis of the impact of agricultural waste on river water quality was carried out by laboratory testing of river water samples that referred to the criteria for water quality standards based on class according to Government Regulation of the Republic of Indonesia Number 82 of 2001 for class I river designation. Laboratory tests of water samples used parameters TSS, TDS, Nitrate, BOD, and COD. While the analysis of the status of water quality using the STORET method. The results showed that the pattern of use of rice fields was clustered upstream and in the middle, farmland was clustered in the downstream and mixed gardens were spread out in the upstream, middle, and downstream areas. The status of river water quality in the upstream and middle parts of the Kreo watershed has been lightly polluted, while the downstream still meets the quality standards. The river water will be harmful to human health if it is intended as a raw source of drinking water.

How climate change and land-use evolution relates to the non-point source pollution in a typical watershed of China

The water quality of Le 'an River Watershed (LRW) is crucial to the water environmental safety of Poyang Lake, especially the concentration of nitrogen and phosphorus. The effect of climate and land use change on watershed water quality has always been under the attention of local managers. More importantly, the lack of detailed studies on climate and land use impact on river water quality has prevented sustainable water security management in the LRW. Therefore, this study aimed to quantify the weight of climate and land use on nutrient loss in the LRW, respectively. We divided the historical period (1990–2020) into six scenarios and a baseline scenario. TN and TP losses in the watershed were simulated using Soil and Water Assessment Tool (SWAT), and the weight of climate and land use were quantified in overall, by period, and by region. The results showed that the weight of climate was greatly higher than land use with values around 90%. However, the weight of land use had a positive cumulative effect in a certain period, and its influence could not be neglected. The climate in all scenarios led to a reduction in nutrient loss, while land use was found to slightly increase the nutrient loss yield. In addition to, unique regional topographic features, urbanization rates, and climatic conditions could cause spatial heterogeneity in the climatic and land use weights.

Mechanism of Response of Watershed Water Quality to Agriculture Land-Use Changes in a Typical Fuel Ethanol Raw Material Planting Area-A Case Study on Guangxi Province, China.

Speeding up the promotion and application of biofuel ethanol has been a national strategy in China, which in turn has affected changes in the raw material planting structure. This study analyzed the response mechanism of water quality to agriculture land-use changes in a cassava fuel ethanol raw material planting area. The results revealed that an increase in cultivated land and construction land would lead to a rise in the load of TN (total nitrogen) and TP (total phosphorus), while an expansion in forest land and grassland area would reduce the load. As for crop structures, corn would have a remarkable positive impact on TN and TP, while rice and cassava performed in an opposite manner. Furthermore, scenarios under the carbon neutralization policy were carried out to forecast the nonpoint source pollutants based on the quantitative relations coefficients. It was proven that cassava planting was suitable for vigorous fuel ethanol development, but the maximum increase area of cassava should be 126 km2 to ensure economic benefits. Under the change in fuel ethanol policy, this study could provide scientific support for local agriculture land-use management in realizing the carbon neutralization vision and also set a good example for the development of the cassava fuel ethanol industry in other cassava-planting countries.

Impact of land-use/land-cover and landscape pattern on seasonal in-stream water quality in small watersheds

Changes in land use land cover (LULC) and landscape pattern in arid areas can considerably impact water quality in small watersheds. Exploring the associations between land use, landscape pattern, and riverine water quality can inform land-use planning for water-quality security. In northwest China's Jing River Watershed (JRW), water samples were collected at 67 points in 2016–2017 and analyzed. Coupled with Sentinel-2 remote-sensing images, this study calculated the Canadian Water Quality Index (CWQI) to assign the water-quality category. The Random Forest classification characterized current LULC patterns and computed landscape metrics in a riparian buffer zone. The stepwise multiple linear regression and redundancy analysis methods investigated the relationships amongst LULC, eight landscape metrics, and eight water-quality parameters. The results indicated high concentrations of total phosphorus (TP) and total nitrogen (TN) in the JRW's middle and lower reaches. For CWQI, lacking evident temporal fluctuations was contrasted by noticeable spatial variations. Intense Human activities have aggravated the deterioration of the water quality of the JRW. LULC-type changes, including Waterbody, Forest-grassland, and Farmland, imposed notable impacts on seasonal water quality. For landscape metrics, patch cohesion index (COHESION) strongly correlated with chemical oxygen demand (COD), mineralization degree (MD), and TN. By contrast, patch density (PD) correlated negatively with TN. Interspersion juxtaposition index (IJI) strongly correlated with biochemical oxygen demand after five days (BOD5). COHESION, PD, and IJI can be critical factors in predicting water-quality changes at the small-watershed scale. Our findings offered a robust scientific basis to refine regional sustainable water development strategy and rational water-resource management.

Impact of Agricultural Non-Point Source Pollution on River Water Quality: Evidence From China

Identifying the effect of agricultural non-point source pollutants on water quality is very important for water pollution management. This study used NH3N as an indicator to empirically study the influence of fertilizer application on river water quality based on panel data of 46 prefecture-level cities and 18 state-controlled water quality monitoring points through which the main streams of Yangtze River and Yellow River flow from 2004 to 2019. It is found that: (1) An increase in agricultural fertilizer application amount will exacerbate water pollution, and the worsening water quality in the upper watershed and the influence of precipitation will lead to transboundary water pollution in the lower watershed. (2) The amount of fertilizer application and fertilizer application intensity had a threshold effect on river water quality pollution. When the former exceeded the threshold value of 11.496 tons, and the latter exceeded the threshold value of 7.991 ton/km2, the positive effect of fertilizer application on pollutants in rivers was further enhanced. (3) The amount of fertilizer applied had a long-term effect on water quality through a lagged effect, and as the number of lags increased, the accumulative effect of the negative influence gradually rose. Based on the findings of the empirical study, it is proposed that the inter-basin and inter-regional synergy should be formed in the prevention and control of agricultural non-point source pollution, and the overall top-level design of agricultural subsidies and agricultural environmental policies in the areas along the basin should be considered.

Spatial heterogeneity of water quality in a small watershed of an ionic rare earth mining area

Abstract The tailwater of ion-type rare earth mines in southern Jiangxi has caused serious water pollution problems in small watersheds. In this study, seven physical and chemical indicators, namely, pH, TOC, dissolved oxygen, ammonia nitrogen, nitrate-nitrogen, salinity and redox potential were selected and spatial interpolation, principal component analysis, and geographic detector methods, were used to quantitatively analyze and evaluate the spatial heterogeneity of water quality in the small watersheds in this region. Tailwater pollution in the whole basin of the study area is serious. The spatial difference is manifested as east tributary > mainstream and reservoir area > southern tributary. Source pollution is the smallest, and water quality pollution is mainly manifested by excessive ammonia nitrogen, salinity, and TOC. The spatial differences in the physical and chemical properties of water bodies are significant. The distribution of ammonia nitrogen content is consistent with the spatial distribution of soil and water pollution, while nitrate-nitrogen is the opposite. Other indicators also show a certain spatial regularity, and the spatial regularity of dissolved oxygen content is not obvious. Water pollution in mining areas is mainly due to a large amount of ammonia nitrogen ions remaining in the mountains. As a result, the southern tributary ecological pool has an obvious purification effect on water quality. Salinity is extremely affected by ammonia nitrogen and TOC, oxidation-reduction potential is affected by pH and TOC, and TOC is influenced by ammonia nitrogen and pH. Salinity, ammonia nitrogen, and TOC are the potential risk factors of major pollution. The changes in the physical and chemical properties of the pollution index are not independent of each other. From the perspective of macro and micro, the comprehensive water pollution assessment system is adopted to provide a new idea for the prevention and control of rare earth industry tail water pollution, and further make exploratory efforts for the study of industrial wastewater pollution.

Material flow analysis of the nitrogen loading to surface water of Miyun reservoir watershed under uncertainty

Nitrogen (N) was one of the primary causes to water environment depravation, having a thorough understanding of N loading to water body is important for reducing the N pollution purposefully. In this research, we took the Miyun reservoir watershed as a typical area, of which a material flow model of the N metabolism was built. Afterwards, the material flow analysis (MFA) was conducted to identify the main pathways that generated N loading. And then the Monte Carlo (MC) method was applied to make uncertainty analysis of the N loading calculated through the MFA. The MFA results showed that the total N loading to surface water of the Miyun reservoir watershed was 5505.42 × 103 kg N, of which about 74.89% was originated from the agriculture subsystem (i.e., crop planting, fruit planting and vegetable planting subsystems). The main pathways of the agriculture subsystem that generated N loading were recognized as maize, chestnut, apple, pear, cabbage, cucumber and tomato planting. The uncertainty analysis results revealed that the N loading calculated from the MFA had some uncertainty, of which the fruit planting and industry subsystem had the biggest uncertainty, while the N loading from the fish farming subsystem had the lowest uncertainty. To make directed actions to protect the water quality of the Miyun reservoir watershed, the main pathways of each subsystem that generated N loading need to be regulated. This study provided a new framework of combing the MFA and MC method to simulate N loading to surface water at watershed scale, and was of vital significance to provide decision support for the watershed N pollution management globally.