Wanquan Estuary water quality health assessment based on three water quality evaluation methods

In the report， in order to understand the current situation of water quality changes in the Wanquan Estuary in Hainan， the dissolved oxygen， ammonia nitrogen， total nitrogen， total phosphorus， and five-day biochemical oxygen， from May 2021 to May 2022， were used as the water quality indicators， the single factor evaluation method， the comprehensive pollution index method， and the improved gray relational analysis method were used to analyze and evaluate the water quality， respectively， and the results of the three evaluation methods were compared. The results showed that the various sites of Wanquan Estuary have been polluted to varying degrees， the content of the dissolved oxygen and total nitrogen of most sites exceeds that of China’s Class Ⅲ water quality criteria， and the pollution of the sites located in the southernmost of Shamei Inland Sea and the narrow channel on the north side of the estuary are worst， and the content of total nitrogen and five-day biochemical oxygen demand exceeds that of China’s Class Ⅲ water quality criteria. Moreover， the pollution level showed obvious seasonal changes， and the pollution level in the dry season was higher than that in the rainy season. Compared with the other two methods， the improved gray relational analysis method can more comprehensively and objectively evaluate the effects of pollutants and judge the main pollutant categories， which can effectively evaluate and manage water quality.