Spatial and temporal analysis of water quality trends in the Min River Basin

In this paper, spatial and temporal pattern analysis was performed to obtain better understanding of the water quality in the Min River Basin. The water quality data of 34 sites for five indicators, Chemical Oxygen Demand (COD), Biochemical Oxygen Demand (BOD₅), Total Nitrogen (TN), Total Phosphorus (TP), and Dissolved Oxygen (DO) between 2001 and 2010 were analyzed. The spatial trends of water quality for the 2000s were presented. An interpolation approach based on the distance along river network was used to reveal the spatial variation of water quality in year 2010. A non-parametric seasonal Mann-Kendall´s test was employed to determine the significance of temporal trends for each parameter of each site. Basically, the water quality of the Min River basin is good and most of the segments can satisfy the national environmental standards of Class III. Moreover, certain spatial and temporal patterns can be discovered through the analysis. The best water quality is in the Dadu River, the Qingyi River, and the upper parts of the Min River. The water quality of the Fu River is the worst in the basin. The middle parts of the Min River are worse than the lower parts and better than the Fu River. From temporal perspective, COD showed significant upward trend, whereas BOD₅ showed significant downward trend. TN and TP showed increasing trends in a similar spatial manner, which exhibits the signs of degradation in water quality. Particularly, the concentration of TN exhibited significant upward trend. Nevertheless, DO showed some upward trends. The reasons of the spatial-temporal characteristics were also discussed and some water management strategies were recommended.