Water quality assessment of rivers in Lake Chaohu Basin (China) using water quality index

This study aims at assessment the water quality condition in the rivers of Lake Chaohu Basin (LCB), and exploring the crucial parameters affecting its water quality. Four sampling activities were conducted seasonally from April to December in 2018 at 83 sites covering main rivers of LCB. We measured 15 physicochemical parameters, such as turbidity (tur), dissolved oxygen (DO), ammonium (NH4-N), nitrate (NO3-N), and permanganate index (CODmn ). There were significant differences of the 15 environmental parameters (except T) on spatial level, and three significant groups (i.e., Group I, II, and III) were divided according to cluster analysis. Water quality was evaluated by a water quality index (WQI) based on these parameters, which are commonly used in WQI calculation. Generally, the water quality state was classified as "moderate" in LCB (mean value of 69.1). Meanwhile, the state varied obviously among the three groups, with "good" in Group I and "moderate" in Group II and III. Seasonally, WQI in autumn was highest, which was significantly different from that in the other seasons. The distribution of water quality was consistent with other studies regardless of some typical rivers and the whole basin. Moreover, a minimum water quality index (WQI(min)) consisted of 5 crucial parameters (i.e., tur, DO, NH4-N, NO3-N, and CODmn ) was not significantly different with the WQI based on all the 15 parameters, and its percentage error was relatively low (6.02%). With the excellent application in Lake Taihu Basin (LTB) nearby LCB, this WQI(min) was robust and potentially universal in determining river water quality assessment in both basins. This finding is probably beneficial to low-cost and quick water quality evaluation in adjacent basins. In addition, TN maybe not suitable for WQI(min) development in rivers, especially in the area with relatively high concentration, which probably resulted in an underestimation of water quality condition.