Abstract:In the Quzhou area, there are five important reservoirs: Huangtankou (S1), Tongshanyuan (S2), Shizikou (S3), Huayuanlong (S4), and Jincanglong (S5). To ascertain the eutrophication level and the main driving factors in reservoirs in the Quzhou area, we analyzed the water quality in 2018 to determine the relationship between eutrophication and environmental factors. The comprehensive trophic level index (TLI) method showed that reservoirs S1, S2, and S3 were mesotrophic, S4 was lightly eutrophic, and S5 was highly eutrophic, which concurred with the relative chlorophyll a (Chl-a) concentrations. To improve the comprehensive development and utilization of the reservoirs, industry, such as aquaculture, was developed in Quzhou. Results showed that eutrophication in aquacultural areas was significantly higher than that in breeding and releasing areas. Furthermore, we analyzed how water quality was affected by aquaculture using a cluster analysis. Results showed that effectively managed aquaculture may not be the main contributing factor for eutrophication. Based on the N/P ratio, we found nitrogen limitation occurred in S5, whereas phosphorous limitation occurred in the other reservoirs. Therefore, we should focus on controlling phosphorous and nitrogen. The regression equation among Chl-a, TLI, and the correlated environmental factors was expressed using multiple linear stepwise regression as follows: Chl-a = 19.793 CODMn–32.065 TP–33.004, TLI = 1.062 CODMn +18.468 TP–0.06 SD + 0.450 T + 1.765 TN + 33.886, where TP, SD, T, and TN stand for total phosphorous, transparency, temperature, and total nitrogen respectively. Combined with a correlation and principal component analysis (PCA), it was concluded that CODMn, TP, SD, T, and TN were the main factors influencing reservoir eutrophication in the Quzhou area, among which nitrogen and phosphorous and organic compounds were the impact factors, and water temperature was the main cause of seasonal change. However, pH and DO were a consequence of eutrophication, and could be indicators of the eutrophication level. pH and DO increased with increasing eutrophication, but in highly eutrophic water, algal overgrowth can cause a rapid decrease in DO in the water.
