Phosphorus Release And Settling In A Tropical Pumped Storage Reservoir: Dajinshan Reservoir, Southern China

Phosphorus is a limiting element of phytoplankton growth in freshwater ecosystem. Phosphorus cycle plays an important role in ecosystem function. It affects not only water quality but also the development of eutrophication. To understand the details of phosphorus cycle is important to manage and control the eutrophication of water bodies. The reservoir studied in this dissertation, Dajingshan reservoir, is a typical pumped storage reservoir located in tropical regions. Simulating experiments in the laboratory and in situ experiments were carried out to explore phosphorus release and settling rates and their affecting factors in the reservoir.Core sediments were collected from near the dam and the central part of the reservoir to simulate the phosphorus release in the seasonal transition from spring to summer. Another core sediment from near the dam was used for simulating experiments of phosphorus release under controlled temperature, in which the release device was improved. The similar device was also applied for in situ experiments for phosphorus release. The sediment traps were located in four sites to measure the phosphorus downward flux and settling velocity.From the in situ experiments, we found that the sediment was anaerobic over 300 days every year. The release rate of phosphorus near the dam was 4.09 mg·m^-2·d^-1, higher than in the other sites. In total, about 110 kg phosphorus was estimated to release from the reservoir bottom, contributed 15％to the total loading.In the seasonal transition from spring to summer, the release rate of total phosphorus near the Dam and at the central zone of the reservoir was 3.24mg·m^-2·d^-1 and 0.62mg·m^-2·d^-1, respectively. In the simulated experiments under the controlled temperature, the release rate of total phosphorus, the total dissolved phosphorus and soluble phosphorus is 3.28mg·m^-2·d^-1, 1.43 mg·m^-2·d^-1 and 0.65 mg·m^-2·d^-1, respectively. These release rates were very close to that from the in situ experiments. During the experiments, the redox slightly increased from -20mv to 18mv, and pH showed a decrease from 8.5 to 7.0.The settling rates of particle phosphorus were measured at 4 zones from the inlet of pumped water to outlet for drinking water supply. The phosphorus downward flux tended to decrease along the four sites. The downward flux is 51.88 mg·m^-2·d^-1 at the Inlet and 9.30 mg·m^-2·d^-1 at the outlet.