A method coupled with remote sensing data to evaluate non-point source pollution in the Xin'anjiang catchment of China.

Non-point source (NPS) pollution has been recognized as the largest threat to water resources throughout the world, and the evaluation of NPS loads is a priority. In China, some models, such as SWAT (Soil and Water Assessment Tools) model, have been widely used at the watershed scale. However, variations in natural and social factors make it difficult to find a proper model to use on NPS pollution management in China. In this study, a "Dualistic Structure" model is coupled with remote sensing data to capture the spatial and temporal processes of NPS pollution. Land parameters were derived from HJ-1A and HJ-1B satellite data (resolution 30 m), which offered greatly enhanced spatial resolution. This approach offers the advantage of being a rapid estimation system with fairly precise knowledge of the distribution, sources and quantities of NPS pollutants, and it can be used at the country scale, including in areas with insufficient data. The method is used in the Xin'anjiang catchment, an important water source for Hangzhou city, China. The simulation in this study includes the spatial distribution of monthly total nitrogen (TN), total phosphorous (TP), ammonia nitrogen (NH(4)-N) and chemical oxygen demand (COD(cr)) loads and the total production of NPS pollutants. The simulations were compared to pollution census (PC) data in 2010 and the results of SWAT model, with an average R(2) larger than 0.7. Additionally, the impacts of soil erosion and human activities on NPS pollution were assessed, indicating that soil and water conservation is very significant factor in the Xin'anjiang catchment. Results indicate that by coupling remote sensing data and parameter retrieval techniques to "Dualistic Structure" models, estimations of NPS loads on the catchment scale can be improved by spatial pixel-based modeling. This rapid NPS estimation system will offer effective support to policy makers for environmental management in China.

Wang X ，Wang Q ，Wu C ，Liang T ，Zheng D ，Wei X ... -  《-》

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.

Shen Z ，Qiu J ，Hong Q ，Chen L ... -  《-》

Assessment and analysis of non-point source nitrogen and phosphorus loads in the Three Gorges Reservoir Area of Hubei Province, China.

Eutrophication due to non-point source (NPS) of nitrogen (N) and phosphorus (P) has become a serious pollution problem in many Chinese rivers. In this paper, the export coefficient model (ECM) was used to assess the influence of NPS on N and P loading to the Three Gorges Reservoir Area (TGRA) of Hubei Province, People's Republic of China. Data from the main non-point sources were analyzed from 1995 to 2007, including rural domestic wastes, distributed livestock farms, fertilizers and soil erosion. Additionally, the potential N and P loading from NPS originated from a variety of sources were estimated and analyzed from 1995 to 2007, including runoff from rural domestic waste, livestock farms, land use, and atmospheric deposition, using the ECM. These gave the temporal distributions of the potential NPS loads within the reservoir area. The results indicated that the potential total nitrogen (TN) load was much higher than the potential total phosphorus (TP) load. The calculated TN load was 2.83×10(4) tonnes, while the TP load was 2.14×10(3) tonnes in 2007, with a ratio of TN/TP of 13.23. Record shows that "algae blooms" occurred 8 times in TGRA that year. Therefore, there may be a correlation between the eutrophication potential in the inlet water of TGRA and the TN/TP ratio of potential NPS loads. These findings demonstrate that the export coefficient model could provide a simple and reliable approach to evaluate the potential N and P loading to the Three Gorges Reservoir Area of Hubei Province in the People's Republic of China and may be useful for the planning and management of the local agricultural watersheds.

Ma X ，Li Y ，Zhang M ，Zheng F ，Du S ... -  《-》

Evaluating nitrogen removal by vegetation uptake using satellite image time series in riparian catchments.

Nitrogen (N) removal by vegetation uptake is one of the most important functions of riparian buffer zones in preventing non-point source pollution (NSP), and many studies about N uptake at the river reach scale have proven the effectiveness of plants in controlling nutrient pollution. However, at the watershed level, the riparian zones form dendritic networks and, as such, may be the predominant spatially structured feature in catchments and landscapes. Thus, assessing the functions of riparian system at the basin scale is important. In this study, a new method coupling remote sensing and ecological models was used to assess the N removal by riparian vegetation on a large spatial scale. The study site is located around the Guanting reservoir in Beijing, China, which was abandoned as the source water system for Beijing due to serious NSP in 1997. SPOT 5 data was used to map the land cover, and Landsat-5 TM time series images were used to retrieve land surface parameters. A modified forest nutrient cycling and biomass model (ForNBM) was used to simulate N removal, and the modified net primary productivity (NPP) module was driven by remote sensing image time series. Besides the remote sensing data, the necessary database included meteorological data, soil chemical and physical data and plant nutrient data. Pot and plot experiments were used to calibrate and validate the simulations. Our study has proven that, by coupling remote sensing data and parameters retrieval techniques to plant growth process models, catchment scale estimations of nitrogen uptake rates can be improved by spatial pixel-based modelling.

Wang X ，Wang Q ，Yang S ，Zheng D ，Wu C ，Mannaerts CM ... -  《-》

[Research on spatial characteristic of non-point source pollution in Liaohe River basin].

Wang XL ，Cai MY ，Zhong BQ ，Yao YJ ，Yin SJ ，Wu D ... -  《-》