Assessing The Water Quality By Means Of An Index Of Biotic Integrity For Phytoplankton In Tanjiang River

In this study the phytoplankton community was investigated during three consecutive seasons (November2010, March2011and July2011) in the Tanjiang River (China) in order to assess the water quality. The temporal and spatial variation in the community structure, the species composition, and the biomass were investigated and analyzed based on the data of20sampling stations distributed over eight sections in the Tanjiang River. First, a biological evaluation of the water quality of the Tanjiang River was made based on an integrated analysis of the Shannon-Wiener diversity index, the Pielou Evenness index and the Margalef Species diversity index. Secondly several phytoplankton indices were tested and selected based on a correlation analysis in order to develop a multimetric index of Biotic Integrity for phytoplankton (P-IBI index). In this way, we wanted to determine reference conditions and to establish a scientific basis for aquatic resources management and aquatic environmental protection. The main conclusions are as follows:1. In total,221phytoplankton species belonging to7phyla and86genera were found in the samples. Most species belonged to the Bacillariophyta and Chlorphyta with96species belonging to36genera and77species belonging to33genera respectively.Cyanophyta and Euglenophyta had a lower species diversity with24species belonging to10genera and17species belonging to6genera, respectively. Pyrrophyta, Chrysophyta and Xanthophyta were only represented by a few genera. The biological evaluation showed that the water quality in the upstream part of the river was better than the downstream part. In the upstream part mainly oligtrophic species were found, whereas in the downstream part phytoplankton species typical for moderate and serious polluted rivers were sampled. With an increase in pollution the Shannon-Wiener index, the Pielou Evenness index and the Margalef Species diversity index decreased. An increasein the proportion of dominant species was observed. According to the integrative analysis result of the three indices, we judged Water quality of abundant water period is the best, the river belongs to non-pollution or olig-pollution, but some samples belong to β-moderate pollution. drought period is pessimal, downstream belongs to serious pollution.2. The multimteric P-IBI index was based on:Shannon-Wiener index, total number of species, percentage of Chlorphyta, biomass of phytoplankton, species number of Cyanophyta, percentage of three dominant taxa and percentage of Chlorphyta plus Bacillariophyta. The result showed that8samples were health,9samples were sub-health,3samples were common in drought period. In level period,11samples were health,4samples were sub-health,4samples were common,1sample was bad. In abundant water period11samples were health,9samples were sub-health.