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 illus-trated the phytoplankton community structure in the CR and assessed its ecological status using the phyto-plankton assemblage index for rivers (Qr 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 TB, 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 Qr of 3.70, which was higher in the middle section. Generalized linear models showed significant positive correlations between Qr and RFGs with the highest F value, i.e. TB and P (both p values<0.001). Qr showed an absence of correlation with the phytoplankton biomass, which was low in our study. The results of our study suggested that Qr can be used in ecological assessments in the CR, which will benefit local water quality assessments.