Water quality assessment using phytoplankton functional groups in the middle-lower Changjiang River, China

The Changjiang River (CR) is the third longest and fifth largest river in the world. However, assessments of its water quality, especially those based on relatively large-scale investigations, are still limited. Our study illustrated the phytoplankton community structure in the CR and assessed its ecological status using the phytoplankton assemblage index for rivers (Q_r index). Samples were collected at 85 sites covering the middle-lower CR in May 2017. The total phytoplankton biomass was higher in the lower section of the river and was characterized by diatoms and cryptophytes. In terms of Reynolds functional groups, the phytoplankton biomass was dominated by T_B, Y, D, and MP, which accounted for 31%, 23%, 13%, and 11% of the mean total biomass, respectively. The ecological status was generally “good” in the CR, with a mean Q_r of 3.70, which was higher in the middle section. Generalized linear models showed significant positive correlations between Q_r and RFGs with the highest F value, i.e. T_B and P (both p values<0.001). Q_r showed an absence of correlation with the phytoplankton biomass, which was low in our study. The results of our study suggested that Q_r can be used in ecological assessments in the CR, which will benefit local water quality assessments.