The community structure and seasonal dynamics of plankton in Bange Lake, northern Tibet, China

The seasonal variations in biomass, abundance, and species composition of plankton in relation to hydrography were studied in the saline Bange Lake, northern Tibet, China. Sampling was carried out between one to three times per month from May 2001 to July 2002. Salinity ranged from 14 to 146. The air and water temperature exhibited a clear seasonal pattern, and mean annual temperatures were approximately 4.8℃ and 7.3℃, respectively. The lowest water temperature occurred in winter from December to March at-2℃ and the highest in June and July at 17.7℃. Forty-one phytoplankton taxa, 21 zooplankton, and 5 benthic or facultative zooplankton were identifi ed. The predominant phytoplankton species were Gloeothece linearis, Oscillatoria tenuis, Gloeocapsa punctata, Ctenocladus circinnatus, Dunaliella salina, and Spirulina major. The predominant zooplankton species included H olophrya actra, Brachionus plicatilis, Daphniopsis tibetana, Cletocamptus dertersi, and A rctodiaptomus salinus. The mean annual total phytoplankton density and biomass for the entire lake were 4.52×10^7 cells/L and 1.60 mg/L, respectively. The annual mean zooplankton abundance was 52, 162, 322, and 57, 144 ind./L, in the three sublakes. The annual mean total zooplankton biomass in Lakes 1–3 was 1.23, 9.98, and 2.13 mg/L, respectively. The annual mean tychoplankton abundances in Bg1, 2, and 3 were 47, 67, and 654 ind./L. The annual mean tychoplankton biomass was 2.36, 0.16, and 2.03 mg/L, respectively. The zooplankton biomass（including tychoplankton） in the lake was 9.11 mg/L. The total number of plankton species in the salt lake was signifi cantly negatively correlated with salinity.