The cumulative effects of cascade reservoirs control nitrogen and phosphorus flux: Base on biogeochemical processes.

The reservoir serves as a water source, a flood control structure, a navigational aid, and also impacts the downstream ecosystem as well as the reservoir zone. However, debate exists about effectiveness of cascade reservoirs in controlling the transportation of nutrients, particularly in the Yangtze River basin, which has been significantly affected by reservoir development. This research develops a new model X-NPSEM (X with Nitrogen and Phosphorus Steady-state Reservoir Model) based on biogeochemical processes of nitrogen and phosphorus reaction for investigating the dynamic storage capacity of cascade reservoirs at both reservoir- and watershed scales. Then the cumulative effects of cascade reservoirs and the related mechanism were investigated in Fujiang watershed, China. Based on the results, cascade reservoirs retained 16.3 % of nitrogen fluxes and 37.6 % of phosphorus fluxes annually. Downstream reservoirs have higher retention rates of phosphorus (0.48/d) compared to upstream reservoirs (0.10/d), mainly due to inflow sediment. Nitrogen retention rates show seasonal variations: wet season (0.21/d) and dry season (0.17/d). These fluctuations in nitrogen retention are primarily influenced by changes in temperature rather than other factors such as operation period, nitrogen and phosphorus concentration, or the nitrogen/phosphorus ratio. In upstream, the concentration of sediment entering the reservoir plays a decisive role in the transformation of P retention from sink to source. The X-NPSRM coupler model could be used for global reservoir operation and watershed management.

New method for scaling nonpoint source pollution by integrating the SWAT model and IHA-based indicators.

Nonpoint source (NPS) pollution shows spatial scaling effects because it is affected by topography, river networks, and many other factors. Currently, the lack of an integrated methodology for quantifying the scaling effect has become a crucial barrier in evaluating NPS pollution. In this study, a new method was proposed for scaling NPS pollution by integrating hydrological model and hydrological alteration indicators. Nested catchments were delineated by eight-direction algorithm, and a semidistributed hydrological model was used to simulate the interannual process within the drainage area and to obtain data series of runoff, sediment, and total phosphorus (TP) at different spatial scales. In addition, the average, the extrema, the change rate and feature variables of each type of indicators were proposed to quantitatively describe the pattern of NPS pollution at different spatial scales. The results show the coefficients of variation (CVs) of most runoff and TP indicators are 0.6-0.8, while those of sediment vary greatly from 0.4 to 1.6 with the threshold of those indicators being 0.33. With the increase in drainage area, the NPS load-related indicators show an increasing trend, while load intensity indicators show a decreasing trend and their changing patterns are affected by the heterogeneity of topographic or hydrological information included. Based on logarithmic variance of the change rate, 825 km2 was identified as the turning point for scaling transformation where the slope changes dramatically. The proposed methodology comprehensively describes features of the NPS scaling effect that could be utilized for targeted monitoring and control of NPS pollution in other watersheds.

Integrating source apportionment and landscape patterns to capture nutrient variability across a typical urbanized watershed.

Effective integrated watershed management requires models that can characterize the sources and transport processes of pollutants at the watershed with multiple landscape patterns. However, few studies have investigated the influence of landscape spatial configuration on pollutant transport processes. In this study, the SPARROW_TN and SPARROW_TP models were constructed by combining direct pollution source data and landscape pattern data to investigate the source composition and nutrient transport processes and to reveal the influence of landscape patterns on nutrient transport in the urbanized Beiyun River Watershed. The introduction of landscape metrics significantly improved the simulation results of both models, with R2 increasing from 0.89 to 0.85 to 0.93 and 0.91, respectively. Spatial variations existed in TN and TP loads and yields, as well as the source compositions. Pollution hotspots were effectively identified. Source apportionment showed that for the entire watershed, TN came from atmospheric nitrogen deposition (35.25%), untreated sewage (28.23%), agricultural sources (22.60%), and treated sewage (13.92%). In comparison, TP came from untreated sewage (44.94%), agricultural sources (40.22%), and treated sewage (11.51%). In addition, the largest patch index of grassland correlated positively with both TN and TP, whereas the largest shape index of buildup land and interspersion and juxtaposition index of forest were negatively correlated with TN and TP, respectively. The results of this study will provide insight into effective nutrient control measures that consider spatially varying nutrient sources and associated nutrient transport processes.

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.

New framework for managing the water environmental capacity integrating the watershed model and stochastic algorithm.

Integrated calculations of pollution load and water environmental capacity (WEC) are essential for effective water quality management. However, few studies have focused on the dynamic WEC and pollution load in a nonpoint source pollution (NPS)-dominant temperate monsoon watershed under changing rainfall conditions. In this study, a new framework based on the watershed model and WEC calculation with stochastic rainfall input (SR-WEC), was proposed to reveal the dynamic WEC and pollution load under changing rainfall conditions. Stochastic rainfall series was generated by a first-order Markov chain and gamma distribution, and further input into the Soil and Water Assessment Tool (SWAT) to explore the dynamic response of water quality to rainfall. The framework was applied to the Daning River watershed, Three Georges Reservoir Region, China. The results suggested that compared with the new SR-WEC, the traditional return period method with limited observed rainfall input would result in an underestimation of ideal WEC and NPS pollution load by 23% and 48% for TN and 48% and 51% for TP, respectively. Approximately 46% of the annual TN reduction and 51% of the annual TP reduction were concentrated from April to June in a relatively small area. The regression relationships between rainfall and the ideal WEC, pollution load and remnant WEC obtained by the SR-WEC were superior to those of the traditional method, with R2 values increasing from 0.005-0.797 to 0.718-0.989. Specific threshold (120 mm/month for the study area) was observed for the effect of rainfall on water quality, beyond which the remnant WEC of organic N would change from decreasing to increasing. The new framework proposed identifies the key periods and areas with consideration of uncertainty of rainfall on water quality, and provides basis for NPS pollution management.

The land carrying capacity and environmental risk assessment of livestock and poultry breeding considering crop planting.

At present, the contradiction between survival and ecology necessitates the integration of crop planting, chemical fertilizer application, and livestock and poultry breeding. Reasonably integrated crop-livestock systems (ICLSs) have become an important part of regional ecological and agricultural development. In this study, the relationship between manure nutrient demands for crops and manure nutrient supply from livestock is considered based on the balance of ICLSs in Jiangxi Province, China. The land carrying capacity index and potential of livestock breeding under uncoordinated systems are further discussed. The study also addresses water environmental risk due to surplus nutrients by integrating a traditional land carrying capacity framework and hydrological model. The results show that phosphorus absorption in land areas is the main limiting factor for the development of the livestock and poultry industries. In addition, manure nutrient demand exceeded supply in most districts, while the unbalanced regions with nutrient pollution are located in the upper and middle reaches of the Ganjiang basin. In addition, expanding the crop demand for manure or increasing the manure collection rate will help reduce environmental harm; however, attention should be paid to the risk of excessive manure returns. Additional livestock manure can be transferred to regions with developed crop planting systems. This study supports more harmonious and common ICLSs construction.

Is returning farmland to forest an effective measure to reduce phosphorus delivery across distinct spatial scales?

As one typical land use change, the mechanism of returning farmland to forests (RFF) on nonpoint source pollution (NPS) is not clear, especially at multiple spatial scales. In this study, by using the Soil and Water Assessment Tool (SWAT), the changes in several flow-related and NPS-related indicators across several nested catchments were quantified and compared in the Three Gorges Reservoir Region, China. The results indicated that RFF could reduce the total flow and total phosphorus (TP), which are higher in the dry season (41% and 79%, respectively) than in the wet season (21% and 47%, respectively) at the watershed with a total area of 2423.74 km2. In comparison, RFF has a larger impact on the baseflow index during the wet season (367.02%) than during the dry season (166.54%). The results also indicated that a spatial scaling effect did exist, while the reduction in TP increased from 24.57% to 48.46% as the drainage area increased from 65.92 km2 to 2104.35 km2. Specific thresholds of RFF efficiency were also observed (approximately 2000 km2 for the study area). It is suggested that other source control measures could supplement RFF by stabilizing the efficiency of RFF across different spatial scales. The results of this study could provide valuable suggestions for land use development and water quality protection, especially for large, complex watersheds.

Quantifying effects of conservation practices on non-point source pollution in the Miyun Reservoir Watershed, China.

Non-point source (NPS) pollution, including fertilizer and manure application, sediment erosion, and haphazard discharge of wastewater, has led to a wide range of water pollution problems in the Miyun Reservoir, the most important drinking water source in Beijing. In this study, the Soil and Water Assessment Tool (SWAT) model was used to evaluate NPS pollution loads and the effectiveness of best management practices (BMPs) in the two subwatersheds within the Miyun Reservoir Watershed (MRW). Spatial distributions of soil types and land uses, and changes in precipitation and fertilizer application, were analysed to elucidate the distribution of pollution in this watershed from 1990 to 2010. The results demonstrated that the nutrient losses were significantly affected by soil properties and higher in both agricultural land and barren land. The temporal distribution of pollutant loads was consistent with that of precipitation. Soil erosion and nutrient losses would increase risks of water eutrophication and ecosystem degradation in the Miyun Reservoir. The well-calibrated SWAT model was used to assess the effects of several Best Management Practices (BMPs), including filter strips, grassed waterways, constructed wetlands, detention basins, converting farmland to forest, soil nutrient management, conservation tillage, contour farming, and strip cropping. The removal rates of those BMPs ranged from 1.03 to 38.40% and from 1.36 to 39.34% for total nitrogen (TN) and total phosphorus (TP) loads, respectively. The efficiency of BMPs was dependent on design parameters and local factors and varied in different sub-basins. This study revealed that no single BMP could achieve the water quality improvement targets and highlighted the importance of optimal configuration of BMP combinations at sub-basin scale. The findings presented here provide valuable information for developing the sustainable watershed management strategies.

Using site-specific soil samples as a substitution for improved hydrological and nonpoint source predictions.

Soil databases are one of the most important inputs for watershed models, and the quality of soil properties affects how well a model performs. The objectives of this study were to (1) quantify the sensitivity of model outputs to soil properties and to (2) use site-specific soil properties as a substitution for more accurate hydrological and nonpoint source (H/NPS) predictions. Soil samples were collected from a typical mountainous watershed in China, and the impacts of soil sample parameters on H/NPS predictions were quantified using the Soil and Water Assessment Tool (SWAT). The most sensitive parameters related to predicting flow, sediment, and total phosphorus (TP) mainly were the soil hydrological, the channel erosion processes, and the initial soil chemical environment, respectively. When the site-specific soil properties were used, the uncertainties (coefficient of variation) related to predicting the hydrology, sediment and TP decreased by 75∼80 %, 75∼84 %, and 46∼61 %, respectively. Based on changes in the Nash-Sutcliff coefficient, the model performance improved by 4.9 and 19.45 % for the hydrological and sediment model, accordingly. However, site-specific soil properties did not contribute to better TP predictions because of the high spatial variability of the soil P concentrations across the large watershed. Thus, although site-specific soil samples can be used to obtain more accurate H/NPS predictions, more sampling sites are required to apply this method in large watersheds.

Spatial-temporal distribution and fuzzy comprehensive evaluation of total phosphorus and total nitrogen in the Yangtze River Estuary.

Based on water sample data collected from the Yangtze River Estuary (YRE) during four sampling periods in 2010 and 2011, the total nitrogen (TN) and total phosphorus (TP) content were evaluated using the traditional single-factor evaluation (TSE) and the fuzzy comprehensive evaluation (FCE). Statistical analyses showed that the average TN and TP for the four periods were 2.60 mg/L and 0.11 mg/L, respectively. August 2010 showed the lowest TN (1.57 mg/L), and February 2011 showed the highest TP (0.15 mg/L). The annual spatial distribution results indicated that an area of high TN concentration (TN ≥ 3.0 mg/L) occurred in the adjacent sea and increased on an eastward gradient. An area of high TP concentration (TP ≥0.10 mg/L) occurred in the inner YRE and decreased on an eastward gradient. There were significant differences in the results of TSE and FCE. The TSE results only reflected the TN evaluation results for certain locations of the YRE. The FCE method combined the effects of the TN and TP factors, and the results indicate that the Chinese water quality classification of Class 5 was dominant in the YRE.

Analysis of field-scale spatial correlations and variations of soil nutrients using geostatistics.

Spatial correlations and soil nutrient variations are important for soil nutrient management. They help to reduce the negative impacts of agricultural nonpoint source pollution. Based on the sampled available nitrogen (AN), available phosphorus (AP), and available potassium (AK), soil nutrient data from 2010, the spatial correlation, was analyzed, and the probabilities of the nutrient's abundance or deficiency were discussed. This paper presents a statistical approach to spatial analysis, the spatial correlation analysis (SCA), which was originally developed for describing heterogeneity in the presence of correlated variation and based on ordinary kriging (OK) results. Indicator kriging (IK) was used to assess the susceptibility of excess of soil nutrients based on crop needs. The kriged results showed there was a distinct spatial variability in the concentration of all three soil nutrients. High concentrations of these three soil nutrients were found near Anzhou. As the distance from the center of town increased, the concentration of the soil nutrients gradually decreased. Spatially, the relationship between AN and AP was negative, and the relationship between AP and AK was not clear. The IK results showed that there were few areas with a risk of AN and AP overabundance. However, almost the entire study region was at risk of AK overabundance. Based on the soil nutrient distribution results, it is clear that the spatial variability of the soil nutrients differed throughout the study region. This spatial soil nutrient variability might be caused by different fertilizer types and different fertilizing practices.

Cost-effectiveness and cost-benefit analysis of BMPs in controlling agricultural nonpoint source pollution in China based on the SWAT model.

Best management practices (BMPs) have been widely used in managing agricultural nonpoint source pollution (ANSP) at the watershed level. Most BMPs are related to land use, tillage management, and fertilizer levels. In total, seven BMP scenarios (Reforest1, Reforest2, No Tillage, Contour tillage, and fertilizer level 1-4) that are related to these three factors were estimated in this study. The objectives were to investigate the effectiveness and cost-benefit of these BMPs on ANSP reduction in a large tributary of the Three Gorges Reservoir (TGR) in China, which are based on the simulation results of the Soil and Water Assessment Tool (SWAT) model. The results indicated that reforestation was the most economically efficient of all BMPs, and its net benefits were up to CNY 4.36×10(7) years(-1) (about USD 7.08×10(6) years(-1)). Regarding tillage practices, no tillage practice was more environmentally friendly than other tillage practices, and contour tillage was more economically efficient. Reducing the local fertilizer level to 0.8-fold less than that of 2010 can yield a satisfactory environmental and economic efficiency. Reforestation and fertilizer management were more effective in reducing total phosphorus (TP), whereas tillage management was more effective in reducing total nitrogen (TN). When CNY 10,000 (about USD 162) was applied to reforestation, no tillage, contour tillage, and an 0.8-fold reduction in the fertilizer level, then annual TN load can be reduced by 0.08, 0.16, 0.11, and 0.04 t and annual TP load can be reduced by 0.04, 0.02, 0.01 and 0.03 t, respectively. The cost-benefit (CB) ratios of the BMPs were as follows: reforestation (207 %) > contour tillage (129 %) > no tillage (114 %) > fertilizer management (96 and 89 %). The most economical and effective BMPs can be designated as follows: BMP1 (returning arable land with slopes greater than 25° to forests and those lands with slopes of 15-25° to orchards), BMP2 (implementing no tillage on arable land with slopes less than 15°), and BMP5 (0.8-fold less than that of 2010).

Uncertainty analysis of total phosphorus spatial-temporal variations in the Yangtze River Estuary using different interpolation methods.

Interpolation processes and results are generally accompanied by uncertainty which affects the spatial and temporal properties of pollutants. Based on the 4 period sample data of total phosphorus (TP) collected from the Yangtze River Estuary (YRE) in 2010 and 2011, the uncertainty of spatial-temporal variation was analyzed with interpolation methods of inverse distance weighted (IDW), local polynomial interpolation (LPI), ordinary kriging (OK) and disjunctive kriging (DK). The root mean square errors (RMSE) and the mean relative errors (MRE) were used to analyze the accuracy of different interpolation methods. The results showed that the uncertainty of DK was the lowest and the uncertainty of LPI was the highest among the 4 methods. The subtraction results between different interpolation methods showed that there was some distinct area of value in the disparate interval (not in [-0.05, 0.05] (mg/L)) in the 4 seasonal results, which was mainly distributed in the boundary region and around some sample sites. Both standard deviation (SD) and coefficient of variance (CV) in August 2010 were the highest in the 4 seasons and annual mean. The uncertainty may be caused by choice of interpolation methods, spatial data discrepancy and the lack of sample data.

Simulation of spatial and temporal distributions of non-point source pollution load in the Three Gorges Reservoir Region.

Non-point source (NPS) pollution has become the largest threat to water quality in recent years. Major pollutants, particularly from agricultural activities, which include nitrogen, phosphorus and sediment that have been released into aquatic environments, have caused a range of problems in the Three Gorges Reservoir Region (TGRR), China. It is necessary to identify the spatial and temporal distributions of NPS pollutants and the highly polluted areas for the purpose of watershed management. In this study, the NPS pollutant load was simulated using the Soil and Water Assessment Tool (SWAT) and the small-scale watershed extended method (SWEM). The simulation results for four typical small catchments were extended to the entire watershed leading to estimates of the NPS load from 2001 to 2009. The results demonstrated that the NPS pollution load in the western area was the highest and that agricultural land was the primary pollutant source. The similar annual variation trends of runoff and sediment loads demonstrated that the sediment load was closely related to runoff. The loads of total nitrogen (TN) and total phosphorus (TP) were relatively stable from 2001 to 2007, except for high loads in 2006. The increase in pollution source strength was an important reason for the significant upward trend of TN and TP loads from 2008 to 2009. The rainfall from April to October contributed to the largest amount of runoff, sediment and nutrient loads for the year. The NPS load intensities in each sub-basin reveal large variations in the spatial distribution of different pollutants. It was shown that the temporal and spatial distributions of pollutant loads were positively correlated with the annual rainfall amounts and with human activities. Furthermore, this finding illustrates that conservation practices and nutrient management should be implemented in specific sites during special periods for the purpose of NPS pollution control in the TGRR.

Runoff characteristics and nutrient loss mechanism from plain farmland under simulated rainfall conditions.

In recent years, nonpoint source (NPS) pollution has become the main contributor to water quality problems. Research on nitrogen (N) and phosphorus (P) losses from farmland and the factors that influence these losses is very meaningful both for increasing the crop yield and for improving environmental water quality. To explore the mechanism by which N and P are lost from farmland in the North China Plain (NCP), 16 simulated rainfalls were conducted in 14 experimental fields (each of which had different conditions) in the NCP from July to August in 2010. The results showed that the rainfall intensity, the antecedent soil moisture content, and the vegetation cover status were the main factors that affected the surface runoff in the NCP. The runoff volume increased with the increasing rainfall intensity and the increasing soil moisture content, and decreased with the increasing vegetation cover. These factors also significantly affected the losses of P and N. The losses of P and N were positively correlated with the rainfall intensity and the antecedent soil moisture content, and negatively correlated with the vegetation cover. A longer and more intense rainfall resulted in a higher loss of N and P. Dissolved nitrogen was the predominant form of N loss. For phosphorous, the predominant loss form was greatly influenced by the rainfall intensity, the vegetation cover, and the antecedent soil moisture content. Most of phosphorus existed as dissolved phosphorus in Baizhuang (BZ) and as particulate phosphorus in Tangcheng (TC) and Fentai (FT). The minimum requirements for runoff occurrence in experimental regions were a rainfall depth of 5.1mm, a rainfall intensity of 50mm/h, and an antecedent soil moisture of approximately 29.6%.

Historical trend of nitrogen and phosphorus loads from the upper Yangtze River basin and their responses to the Three Gorges Dam.

Excessive inputs of nitrogen and phosphorus (N and P) degrade surface water quality worldwide. Impoundment of reservoirs alters the N and P balance of a basin. In this study, riverine nutrient loads from the upper Yangtze River basin (YRB) at the Yichang station were estimated using Load Estimator (LOADEST). Long-term load trends and monthly variabilities during three sub-periods based on the construction phases of the Three Gorges Dam (TGD) were analyzed statistically. The dissolved inorganic nitrogen (DIN) loads from the upper YRB for the period from 1990 to 2009 ranged from 30.47 × 10(4) to 78.14 × 10(4) t, while the total phosphorus (TP) loads ranged from 2.54 × 10(4) to 7.85 × 10(4) t. DIN increased rapidly from 1995 to 2002 mainly as a result of increased fertilizer use. Statistics of fertilizer use in the upper YRB agreed on this point. However, the trend of the TP loads reflected the combined effect of removal by sedimentation in reservoirs and increased anthropogenic inputs. After the TGD impoundment in 2003, decreasing trends in both DIN and TP loads were found. The reduction in DIN was mainly caused by ammonium consumption and transference. From an analysis of monthly loads, it was found that DIN had a high correlation to discharges. For TP loads, an average decrease of 4.91 % in October was found when the TGD impoundment occurred, but an increase of 4.23 % also occurred in July, corresponding to the washout from sediment deposited in the reservoir before July. Results of this study revealed the TGD had affected nutrient loads in the basin, and it had played a role in nutrient reduction after its operation.

Long-term variation (1960-2003) and causal factors of non-point-source nitrogen and phosphorus in the upper reach of the Yangtze River.

The knowledge of long-term variation and causal factors of non-point source (NPS) pollution in large-scale watersheds is helpful in the development of water quality control programs. In this study, the Improved Export Coefficient Model and the Revised Universal Soil Loss Equation were combined to estimate the temporal and spatial variations (1960-2003) of NPS pollution in the upper reach of the Yangtze River (URYR). Two change points for NPS pollution were successfully detected. In the URYR, the dissolved nitrogen (DN) and dissolved phosphorus (DP) increased before 2000 and decreased after 2000, whereas the inflection points from increase to decline were around 1980 for the adsorbed N (AN) and adsorbed P (AP). The results also indicated that the dissolved pollutants were mainly contributed by the anthropogenic factors, while the adsorbed pollutants were primarily exported by the natural factors. By comparing the load intensities from each source, it revealed that for the dissolved pollutants, the major source of the high load intensity transferred from urban land to dry land after 1980. Simultaneously, the high load intensity areas of the adsorbed pollutants transferred from forest to orchard around 1980, which was mainly attributed to the increasing fertilizer application. These results may be useful for planning and management of the URYR and other large-scale watersheds.

Spatial and temporal variations in nitrogen and phosphorous nutrients in the Yangtze River Estuary.

Based on spatial interpolation data from 2003 to 2010, combined with almost 30 years of nitrogen and phosphorus pollutant data, this research analyzed the variations in total nitrogen (TN), nitrate nitrogen (NO(3)-N), total phosphorus (TP) and phosphate-P (PO(4)-P) in the Yangtze River Estuary (YRE). On the annual and seasonal timescales, nitrogen and phosphorus concentrations exhibited increasing trends overall, and the fluctuations in the concentrations of TN, TP and PO(4)-P significantly increased during the last three decades, especially after 2003, because of the more prevalent human activities and nonpoint sources in the area. Specifically, a high-concentration area of TN was found downstream of the North Branch of the YRE. Considering the spatial distribution of the nutrients, combined with a tidal flood current and a time span of 7 years, the TN maximum increased from approximately 3.07mg/L to 4.48mg/L. The TP maximum also rose from approximately 0.25mg/L to 0.34mg/L because of a high-concentration area of TP in the South Branch of the YRE due to the confluence with the Huangpu River. Additionally, there was an expansion of high-concentration areas of TN (≥3.0mg/L) and of TP (≥0.20mg/L).

[Spatial distribution and pollution source identification of agricultural non-point source pollution in Fujiang watershed].

In order to provide regulatory support for management and control of non-point source (NPS) pollution in Fujiang watershed, agricultural NPS pollution is simulated, spatial distribution characteristics of NPS pollution are analyzed, and the primary pollution sources are also identified, by export coefficient model (ECM) and geographic information system (GIS). Agricultural NPS total nitrogen (TN) loading was of research area was 9.11 x 10(4) t in 2010, and the average loading was intensity was 3.10 t x km(-2). Agricultural NPS TN loading mainly distributed over dry lands, Mianyang city and gentle slope areas; high loading intensity areas were dry lands, Deyang city and gentle slope areas. Agricultural land use, of which contribution rate was 62. 12%, was the most important pollution source; fertilizer loss in dry lands, of which contribution rate was 50.49%, was the prominent. Improving methods of agricultural cultivation, implementing "farm land returning to woodland" policy, and enhancing treatment efficiency of domestic sewage and livestock waster wate are effective measures.

Parameter uncertainty analysis of non-point source pollution from different land use types.

Land use type is one of the most important factors that affect the uncertainty in non-point source (NPS) pollution simulation. In this study, seventeen sensitive parameters were screened from the Soil and Water Assessment Tool (SWAT) model for parameter uncertainty analysis for different land use types in the Daning River Watershed of the Three Gorges Reservoir area, China. First-Order Error Analysis (FOEA) method was adopted to analyze the effect of parameter uncertainty on model outputs under three types of land use, namely, plantation, forest and grassland. The model outputs selected in this study consisted of runoff, sediment yield, organic nitrogen (N), and total phosphorus (TP). The results indicated that the uncertainty conferred by the parameters differed among the three land use types. In forest and grassland, the parameter uncertainty in NPS pollution was primarily associated with runoff processes, but in plantation, the main uncertain parameters were related to runoff process and soil properties. Taken together, the study suggested that adjusting the structure of land use and controlling fertilizer use are helpful methods to control the NPS pollution in the Daning River Watershed.