Summer phytoplankton diversity and water quality evaluation in northern part of Taihu Lake,China

The composition and distribution of phytoplankton species in water samples collected from the northern part of Taihu Lake,was investigated in July 2004.Simultaneously,the water quality was appraised by using various appraisal indexes.The density of phytoplankton is very high in all of the sampling sites,ranging from 2.54×107 to 8.53×108 individuals L-1,and with an average value of 2.87×108 individuals L-1.There are 6 main phytoplankton groups including Cyanophyta,Cryptophyta,Bacillariophyta,Chlorophyta,Euglenophyta,Pyrrophyta,and among which the predominant species is Microcystis spp.From the nearshore to the offshore,the phytoplankton biomass decreases gradually,and the phytoplankton species increases by degrees.This trend indicted the anthropogenic activities and lake characteristics had a strong impact on the water quality of Taihu Lake.According to the appraisal indexes and phytoplankton species,the extent of water pollution is very serious.The trophic state relating to phytoplankton density and biomass varies from mesotrophic to eutrophic.