Construction of phytoplanktonic index of biotic integrity and evaluation of water ecological health in Dianshan Lake， China

A total of four time surveys on water quality and its phytoplankton of Dianshan Lake in Shanghai, China were carried out in January, April, July and October 2019. Phytoplanktonic index of biotic integrity(P-IBI)was constructed to assess the water health condition of Dianshan Lake. The comprehensive nutritional status index(TSI)is used to determine the reference sites and the impaired sites, 19 biological indexes with widely application and high selection rates were used as candidate biological indexes, and the candidate indexes were tested for the distribution, discriminant analysis, correlation analysis. Finally,five parameters composing the P-IBI of Dianshan Lake were obtained:number of diatom species, phytoplankton richness index, percentage of Chlorophyta density,percentage of Cryptophyta density,and total phytoplankton biomass. P-IBI was used to evaluate the ecosystem health of the lake. On the whole, Dianshan Lake is in the state of sub-healthy. Among them, there are one, eight and three points in the healthy, sub-healthy and good state respectively. It is sub-healthy when in spring and winter, and good when in summer and autumn. P-IBI has a very significant positive correlation with water transparency(SD),and a very significant negative correlation with Chlorophyll a(Chl a)and total phosphorus(TP)