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 × 104 tonnes, while the TP load was 2.14 × 103 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.

► We introduce the study area and analyze the data of the main non-point sources.
► We use ECM to assess the influence of NPS loads to the study area.
► The results of the calculation was analyzed and discussed.
► The correlation between eutrophication and TN/TP ratio of NPS loads was discussed.