Estimation and application of macroscopic water environmental capacity of total phosphorus and nitrogen for Taihu Lake

This paper estimated the Macroscopic Water Evironmental Cpacity(MWEC) for TP and TN in Taihu Lake based on the historical data(2000—2011) of hydrology,water quality and pollutant loads.For the year of 2015 and 2020,the maximum allowable pollutant load to the water body,the maximum allowable discharge from sources and the minimum pollutant reduction percentages were also calculated according to the MWEC.The detailed allowable discharges for all sub-districts were also developed to guide water pollution control and management.The reliability and the feasibility of water quality targets in 2015 and 2020 were reviewed and assessed.The results showed that it was possible to achieve the strict targets of TP and TN in 2015 and 2020 with great efforts in pollution control and management.After 2020,water quality of Taihu Lake would stay at the Criteria III(TP) and Criteria V(TN) according to the Surface Water Environmental Quality Standard(GB3838—2002) for a long period.Due to the high possibility of algal bloom,effective emergency measures for improving water quality,such as transferring water from Yangze River to Taihu Lake and clearing the algae or other aquatic plants from the lake,were suggested for the long term program.