China's 6th Largest Lake
Dianchi Lake is the sixth largest lake in China with a surface area of approximately 309 km2 (120 square miles) and a volume of approximately 1.56 billion m3. Dianchi is a lake with very poor water quality. It is a shallow urban lake with nutrient loading from wastewater treatment effluents and storm water from the City of Kunming. Presently Dianchi is characterized as hypereutrophic with extremely high nutrient concentrations, toxin producing algae, floating mats of algae that are in various stages of health, and very poor transparency. The lake is unsuitable for water supply, has a degraded fishery, and can not be used for recreation. Based on an international index that rates lake water quality from best to worst possible conditions (between 0 and 100 with 0 being best and 100 being poorest), Dianchi was rated as 112 based on phosphorus concentrations in the lake and 196 when based on nitrogen concentrations. These results were based on water samples that we collected from Dianchi in April 2006. These results suggest Dianchi is an extreme example of a very polluted, nutrient-rich freshwater lake.
Note the dense growths of algae due to very amounts of high nitrogen & phosphorus in the photo above.
Given the severity of the impairment of water quality, we developed a detailed sequential program to reduce nutrients and clean up the lake. Our clean-up program addressed:
1. Inputs of nutrients to the lake;
2. Cycling of nutrients and toxins from the sediments; and
3. Reductions of in-lake nutrient concentrations. We conducted educational sessions with management and staff of the Dianchi Water Management team to ensure appropriate implementation.