Study of phytoplankton community in the channel from Dongting Lake to Changjiang River, China

1 INTRODUCTION Dongting Lake (28°18'–29°45'N, 111°35'– 113°18'E) is the second largest freshwater lake in China, and directly connected with the Changjiang River (Yangtse River) through the channel. The sur- face area was about 2 740 km2 (at the low

Study of phytoplankton community in the channel from Dongting Lake to Changjiang River, China

Phytoplankton cell density, biomass, chl-a concentration and their seasonal fluctuations at five stations in the channel between Dongting Lake and the Changjiang (Yangtze) River were studied from May 1995 to December 1997. The seasonal fluctuations had two peaks in a year in general. The annual patterns of total cell density and biomass indicated that diatoms contributed more than 70 percent of the total biomass (except from June to October) during the investigation period. Twenty-one dominant species contributed about 60–80 percent of the biomass in various months. The cell density, biomass and seasonal fluctuation were similar at Stations 1–4, but at Station 5 connected directly with the Changjiang River, the annual mean values (127.34×10⁴ cells/L and 0.46 mg/L in 1996, 41.98×10⁴ cells/L and 0.2 mg/L in 1997 respectively) were lower than those (195.92×10⁴ cells/L and 0.5 mg/L in 1996, 132.96×10⁴ cells/L and 0.57 mg/L in 1997 respectively) at Station 1–4; and the curve of the seasonal fluctuation sometimes did not coincide with those at Stations 1–4. Based on criteria for evaluating trophic status, the dominant species, annual average cell density values of 114.86×10⁴–179.57×10⁴ cells/L, biomass of 0.48–0.5 mg/L, chl-a concentration of 0.42–0.51 μg/L respectively recorded at five stations in 1996 and 1997, and values associated with the physico-chemical properties of the waterbody indicated that the water in the channel could be characterized as oligo-mesotrophic. Project 39670155 and 39430101 supported by NSFC.