Ecological assessment of water quality in an urban river replenished with reclaimed water: the phytoplankton functional groups approach

Comprehensive water quality assessment plays a vital role in decision making for the sustainable management of urban rivers, and thus the exploration of integrated ecological assessment methods for water quality has become a major requirement. This study assessed the water quality of the North Canal River on the basis of its ecological status using the phytoplankton functional groups (PFGs) approach. The river runs through the megacities of the Beijing-Tianjin-Hebei region in China, and is mainly replenished with reclaimed water. The results showed that the PFGs approach is much better for evaluating the water quality of urban rivers than the conventional physicochemical index method and phytoplankton diversity metrics, because the PFGs approach is more sensitive to the spatiotemporal variations in the water quality of urban rivers. The average Q ( r ) index, for ecological status estimation in rivers, based on the PFGs of the North Canal River was 3.30, indicating 'good' water quality. In the dry season, the dominant PFG upstream was group D (Cyclotella spp.), whereas the major downstream PFGs had changed to group Y (Glenodinium spp., Cryptomonas ovata, and Cryptomonas erosa) and W1 (Euglena spp. and Gonium pectoral). While the dominant PFG throughout the river changed to T-B: Melosira spp. in the wet season. The Q ( r ) at each site was one to two grades lower during the wet season than the dry season, indicating that water quality was worse in the wet than the dry season.