Evaluation of nitrogen and phosphorus loads from agricultural nonpoint source in relation to water quality in Three Gorges Reservoir Area, China

摘要

Following the implementation of the Three Gorges Dam Project, water quality deterioration due to an excess of nitrogen (N) and phosphorus (P) from agricultural nonpoint source (ANPS) is of major concern in Three Gorges Reservoir Area (TGRA), People's Republic of China. An export coefficient model (ECM) was developed to provide reasonable estimates on the influence of ANPS on N and P loads to TGRA based on field investigation datasets from 1996 to 2013. Additionally, the potential total nitrogen (TN) and total phosphorus (TP) loads from ANPS originating from a variety of sources were estimated and analyzed. These gave the spatial and temporal distributions of the potential ANPS loads within the reservoir area, and the relationship between TN/TP loads from ANPS and water quality was analyzed after impoundment in TGRA. The TN and TP loadings were calculated as 4.11x10(4)tonnes and 0.31x10(4)tonnes in 2013, respectively, with a ratio of TN/TP of 13.46, and algae blooms occurred 13 times in the tributaries of TGR that year. Therefore, there may be a correlation between the eutrophication potential in the inlet water and the TN/TP ratio of potential ANPS loads in TGRA. According to field monitoring, increased P loading to these water systems may cause excessive algal and macrophyte growth and consequent environmental degradation. These findings provide useful and valuable information for decision makers and planners to take sustainable measures for the control of ANPS pollution in TGRA. It is also demonstrated that the ECM could provide a simple and reliable approach to evaluate the potential TN and TP loadings to the TGRA, and thus, it is useful for the aquatic environment management of the local agricultural watersheds.