Using multiple indicators to assess spatial and temporal changes in ecological condition of a drinking water reservoir in central China

Abstract

Monitoring the ecological status of drinking water reservoirs is very important for assessing risks to the safety of drinking water supplies. Because of the huge number of potential organic and inorganic contaminants in water, we focused our study on common water quality variables and three ecological indices. In this study, we used the modified Carlson trophic status index, Shannon diversity index, and the phytoplankton functional group index to assess the changing ecological status of Zhushuqiao Reservoir, a drinking water source in central China. Stratified water sampling for abiotic and biotic variables was conducted bimonthly from April 2016 to February 2017. All three indices indicated that upper reservoir water quality and ecological condition were worse than those in the lower reservoir. Also, the dominant phytoplankton species in the upper reservoir differed significantly from those in the lower reservoir. The reservoir was eutrophic from June to October, especially in June. During the other months, it was mesotrophic, with the best water quality in winter. Water temperature was the main driver of seasonal changes in both biotic and abiotic indicators, although hydrological condition also affected water quality. Total phosphorus (TP) was the limiting factor for phytoplankton, but phytoplankton biomass increased greatly when both TP and total nitrogen increased. Each index had weaknesses; but applying all three together yielded a comprehensive ecological assessment of Zhushuqiao Reservoir and could do so for other similar reservoirs.