[Spatio-temporal Evolution and Relationship of Water Environment Quality and Phytoplankton Community in Wenyu River]

The Wenyu River is an important ecological corridor of Beijing. In this study, the spatio-temporal dynamics of water quality and phytoplankton community in the Wenyu River in 2006, 2011, and 2018, as well as their relationship were thoroughly analyzed by historical data analysis and field surveys. Results show that the water quality in the Wenyu River improved significantly from serious pollution owing to pollution containment. The major water pollutant has shifted from ammonia nitrogen (NH₄⁺-N) to total nitrogen (TN). Compared with 2011, the average multiple of NH₄⁺-N and total nitrogen TN exceeding the national standard were reduced by factors of 0.29-0.33 and 2.77-2.39, respectively, in 2018. The average concentration of NH₄⁺-N and TN decreased from 15.52-19.16 mg·L^-1 and 20.21-19.58 mg·L^-1 in 2011 to 1.93-2.66 mg·L^-1 and 5.66-6.79 mg·L^-1 in 2018. Moreover, dissolved oxygen (DO) and NH₄⁺-N concentrations in the Wenyu River and its tributaries, the Qinghe River, almost met requirements of their water function zoning target. Corresponding with the water quality improvement, the phytoplankton and community species increased dramatically. Phytoplankton species increased from 6 to 8 phyla, as well as community species. The dominant species changed from Chlorophyta in 2006 to the Cyanophyta in 2011, then to Bacillariophyta in 2018. The Shannon-Wiener diversity index (H') and evenness Pielou index (J) had improved. However, the major dominant species such as Cyclotella and Melosira persisted, and the Wenyu River was still in the eutrophication state in 2018. Statistical analysis results indicated that Cyanophyta, Bacillariophyta, and other algae abundance were significantly correlated with DO, pH, NH₄⁺-N, TN, and TP.