Spatiotemporal variations of water quality and driver forces detection in Yangtze River Basin, China from 2008 to 2020 by multi-statistical analyses

Abstract

Water quality deterioration is a prominent issue threatening water security throughout the world. Yangtze River Basin, as the largest river in China, is facing severe water pollution due to the intensive human activities. The analysis of water quality trends and identification of driver factors are significant for sustainable water quality management. Thus, spatiotemporal characteristics of the water quality from 2008 to 2020 were analyzed by using Mann–Kendall test and Rescaled Range analysis (R/S), respectively. Also, the drivers of the key monitoring indicators including permanganate index (CODMn), ammonia nitrogen (NH3-N) and total phosphorus (TP) were detected by multi-statistical analyses. The results showed that water quality was significantly improved, which was reflected from its mean concentration of NH3-N and TP, decreasing from 0.31 mg/L to 0.16 mg/L and 0.16 mg/L to 0.07 mg/L, respectively. However, the concentration of CODMn did not remarkably decline in the past 13 years. The R/S analysis indicated that the concentration of NH3-N would continue to decrease in the next 13 years, while CODMn might continue to increase, which should be of great concern to us. In terms of spatial distribution, the water quality in the upstream was significantly better than that of the mid-downstream. Multi-statistical analyses revealed that the temporal evolution of water quality was predominantly influenced by tertiary industry (TI), nitrogen fertilizer application rate (N-FAR), phosphate fertilizer application rate (P-FAR) and irrigation area of arable land (IAAL), with a contribution rate of 15.92%, 14.65%, 3.46% and 2.84% respectively. The spatial distinction of CODMn was mainly influenced by TI, while TP is primarily determined by anthropogenic activity factors including N-FAR, P-FAR and so on. This study was expected to provide deep insights into water quality evolution and foundations for water quality management in Yangtze River Basin.