Abstract:

Biological indices such as similarity index,diversity index were used to analyze the community structure characteristics of phytoplankton,and both biological indices and physicalchemical indices were used to evaluate the water quality in the lower reach of the Yangtze River in Autumn.Results showed that there were 5 phyla including 27 species of phytoplankton in the lower reach of the Yangtze River in Autumn.The abundance of phytoplankton ranged from 5.68×104  to 7.08×104 cells/L,with the average of 6.01×104 cells/L,and the biomass of phytoplankton ranged from 30.43 to 34.73 μg/L,with the average of 32.46 μg/L. The similarity indices ranged from 0.30 to 0.63,indicating that the phytoplankton similarity was between mild similarity and middle similarity.The phytoplankton diversity indices ranged from 2.38 to 2.73,which meant that both phytoplankton diversity and phytoplankton evenness were good and the phytoplankton community structure was in a stable level in the lower reach of the Yangtze River in Autumn.The permanganate (CODMn),total nitrogen (TN),total phosphorus (TP) and Comprehensive Trophic State Index (TLI(∑)) ranged form 2.71 to 3.23 mg/L,1.24 to 1.35 mg/L,0.058 to 0.072 mg/L and 44.87 to 45.96 respectively.It could be concluded that the water quality of the lower reach of the Yangtze River in Autumn was good.However,the pollution degrees evaluated by physicalchemical method was more sensitive than that evaluated by biological method,which revealed the difference between the two evaluation methods.Therefore,in order to improve the veracity and reliability of the monitoring result,the biological monitoring methods should be coupled with the physicalchemical monitoring as well.〖