Insights into community-based discrimination of water quality status using an annual pool of phytoplankton in mid-subtropical canal systems.

With rapid response to environmental changes, phytoplankton communities have been used as a favorable bioindicator to evaluate environmental stress and anthropogenic impacts in aquatic ecosystems. The feasibility for their community-based bioassessment was studied in a mid-subtropical canal (Tiesha River), southern China, during a 1-year cycle (November 2009-December 2010). Samples were monthly collected at four sampling stations within a contamination gradient. Environmental variables, such as water temperature, dissolved oxygen (DO), chemical oxygen demand (COD), biological oxygen demand (BOD5), total phosphorus (TP), and total nitrogen (TN), were measured synchronously for comparison with biotic parameters. The phytoplankton community structures showed a significant difference among four stations. The spatial variation in abundance was significantly correlated with the changes in environmental variables, especially TN, TP, and COD. Four dominant species (Aulacoseira granulata, Leptocylindrus danicus, Oscillatoria tenuis, and Radiococcus nimbatus) were significantly correlated with nutrients, while the species richness index represented a significant correlation with BOD5. The phytoplankton-based Saprobien indices could not reveal the spatial variation in water quality status although may reflect water pollution levels (from β- to α-mesosaprobic zone) in the canal system. It is suggested that phytoplankton communities might be used as a potentially robust bioindicator for discriminating environmental quality status in mid-tropical canal systems.