Abstract: In August (summer) 2009 and January (winter) 2010, water and sediment samples were collected from Hongfeng Reservoir in Guizhou to analyze the total nitrogen (TN), total phosphorus (TP), phosphate (PO^3-₄), and chlorophyll-a (Chl-a) in water body and the dissolved phosphorus (DP) in sediment pore water. The mean TN concentration in water body was 1.58±0.73 mg·L^-1, and no obvious difference was observed between summer and winter. The mean TP concentration in water body was higher in summer (0.091±0.070 mg·L^-1) than in winter (0.026±0.055 mg·L^-1). In summer, the lake water at the depth 8 m was thermally stratified, with the TN and TP concentrations being higher in hypolimnion than in thermocline. The Chl-a in water body was mainly concentrated in thermocline, with a mean concentration 33.2±13.0 mg·m^-3 in summer and 11.1±3.7 mg·m^-3 in winter. There was a significant positive linear correlation between Chl-a and TP in the upper 8 m water layer (r=0.965,P<0.01), suggesting that the eutrophication of Hongfeng Reservoir was limited by phosphorus. The DP concentration in sediment pore water and the phosphate (PO^3-₄-P) concentration in water body were much higher than the PO^3-₄-P concentration in overlying water, which meant that the DP had a strong upward diffusion tendency. According to Fick’s first law, the phosphorus emission flux from sediment to overlying water was calculated. The phosphorus emission rate was higher in summer than in winter, possibly because the bottom anoxic water environment and its higher temperature in summer favored the formation of DP during the early diagenesis. Based on the phosphorus flux from sediment to overlying water, the annual phosphorous emission from sediment to water body was estimated as 5.0±5.6 metric tons. It was suggested that the eutrophication of Hongfeng Reservoir was controlled by phosphorous, and the sediment had a great potential in releasing phosphorous, being an important inner source of lake water phosphorous. To control the eutrophication of Hongfeng Reservoir, more strict policy was necessary to limit the anthropogenic phosphorous input from the watershed.

Key words: Vermiculture, Vermicompost, Soil borne disease, Inhibition