Estimating Nitrogen Yield for a Catchment of Lake Taihu Based on Distributed Hydrological Modelling

Abstract

Nitrogen and phosphorous pollution is common in China and worldwide. The pollution deteriorates water quality and even causes significant change of the freshwater ecosystem. Management must be strengthened in order to reduce the pollution to secure water supply safety and to maintain healthy ecosystems. This paper investigated the yield of total nitrogen (TN) for different land use types, exemplified in the Xitiaoxi catchment of Lake Taihu basin, where catchment-generated nitrogen pollution is severe. Extensive water quality sampling was performed for different river levels and various land use types. A distributed hydrological model was also employed to simulate the river discharges at locations where flow observation is not available, and the simulated river discharges were used for the calculation of nitrogen yield. It is found that generally the catchment’s nitrogen export is still as high as 2.6 t/km2/year. The yield for forest is 0.8-1.0 t/km2/year, while the yields for arable land and for the river sections immediately downstream of urban area are higher than the average ranging 2.8-3.3 t/km2/year. It is also concluded that the hydrological modelling using a spatially distributed model is helpful and essential in obtaining flows at any locations, which can subsequently be used jointly with the water quality data to identify the critical source areas with high nitrogen yields.