Watershed-Based Management of Lake Dianshan for Source Water Protection

The increasing pollution load played a key role in the water quality deterioration and eutrophication of Lake Dianshan. The results of pollution surveys of 1985, 1995 and 2006 showed that the inputs of nitrogen and phosphorus from upper stream origin from Lake Taihu were up to 7565.0 t and 401.0 t in 2006, respectively, accounting for more than 90% of the sum; nitrogen input from non-point source decreased by 13% to 252.6 t, and phosphorus multiplied 1.78 times to 23.3 t; the nutrient inputs from the point sources declined sharply from 1985 to 2006, and the emissions of nitrogen and phosphorus decreased from 103.0 t and 10.2 t to 8.0 t and 10.0 t, respectively; phosphorus from inner source was only 6.35 t. The analysis of the concentration of nitrogen, phosphorus and chlorophyll a indicated that eutrophication in Lake Dianshan was so high that the frequency of harmful algal blooming increased rapidly in recent years, which threatened the safety of water supply system of Shanghai. Beside the increasing pollution load, regional and stakeholder conflicts also challenged the lake management efficiency in this watershed. A sustainable lake management system was proposed in this study in order to reduce pollution load and solve the trans-boundary conflicts, including reducing point source pollution, adjusting the local economic structure and land use implementations, restoring the lakeshore buffer and setting up a new management mechanism with stakeholder involving.