Study on the coupling effect of nitrogen and phosphorus in water environment of Jianghan-Dongting Plain, China

The excessive eutrophication of surface water will lead to the imbalance of species distribution in water ecosystem, and destroy the flow of material and energy in the system. Detection results of surface water in the Jianghan-Dongting Plain showed that the median concentration of TN was more than 1.60 mg/L, with the excess rate over 60.0%. The TP concentration was not high and the excess rate was less than 10.0% except for Qianjiang. The optimal nitrogen and phosphorus requirements for algae growth in the study area were 1.20 mg/L and 0.07 mg/L respectively, with the most suitable N/P ratio ranging around 16:1. Phosphorus was considered as the limiting factor when N/P exceeded 30:1. Nitrogen was considered as the limiting factor when N/P was less than 10:1. The findings indicated that the plain area between the Yangtze River and the Han River was a high-risk zone, while the southern region of the Yangtze River exhibited the lowest risk of water environment eutrophication. In addition, the risk of eutrophication of water environment was greatly affected by human activities. The findings of this study directly contributed to improving the water ecological security system of the Jianghan-Dongting Plain and provided scientific support for the risk management.