Assessment on river water ecological health based on grey relation analysis in Liaohe Conservation Area

Grey relation analysis is an efficient method for evaluating uncertain complex systems. It has the advantages of low data requirement, small computation and wide application and is an appropriate method for river water ecological health evaluation. Based on the connotation of water ecological health and the actual situation of rivers in Liaohe Conservation Area, a river water ecological health evaluation index system composed of 4 criterion layers and 20 indicator layers, including natural morphology, water quality, sediment, aquatic organisms and ecological environment, was constructed. Analytic hierarchy process (AHP) was used to determine the weight of criterion layer and, combined with grey relation analysis, to evaluate the water ecological health status of Liaohe Conservation Area. The results showed that the comprehensive health status of water ecology in Liaohe Conservation Area was medium, the grey relation degree of natural morphology was 0.868 4, and the health status was medium. The grey relation degree of water quality was 0.691 2, and the health condition was moderate. The grey relation degree of sediment was 0.968 6, and the health condition was excellent. The grey relation degree of aquatic organisms and ecological environment was 0.750 4, and the health status was also moderate. Among the 20 evaluation indexes, river bed stability, river bend degree, chemical oxygen demand, total phosphorus concentration, fish diversity index and algal diversity index were of medium health grade, while total nitrogen concentration was pathological. Since the establishment of the Liaohe Conservation Area in 2010, heavy metals pollution in the sediments of the river has been greatly improved, but there were still problems such as poor riverbed stability, water quality index pollution, low fish diversity and low algal diversity index.