Determining The Main Controlling Factors of Nitrogen Diffusion Fluxes at Sediment-water Interface by Grey Correlation Analysis

The hydro-fluctuation belt is a vital ecosystem with rich resources and environmental regulation ability. It plays a critical role in maintaining biodiversity, the balance in aquatic-terrestrial ecosystem and water purification. However, the water environmental system in the hydro-fluctuation belt is complex and dynamic with a large number of uncertain factors, and these factors are interrelated, which can be defined as a grey system. This paper evaluated the effects of environmental influencing factors on nitrogen diffusion fluxes at sediment-water interface and determined the main controlling factor by application of grey correlation analysis. The monitoring of nitrogen diffusion fluxes at sediment-water interface in the hydro-fluctuation belt of Danjiangkou reservoir lasted for one year, the index system of environment influencing factors were determined, and the procedures of the grey correlation analysis method were introduced. Analysis results indicate that the main controlling factors for diffusion flux of ammonium, nitrate, nitrite and inorganic nitrogen were dissolved oxygen, temperature, pH and pH, respectively. The nitrogen compounds accumulated in the sediment for a long duration can be transformed into ammonium nitrogen by microorganisms, which increased the nitrogen release risk. Therefore, it is an effective way to regulate the pH in the overlying water to control nitrogen pollution. Since the process of nitrogen migration and transformation can be affected by many direct and indirect influential factors, it is quite difficult to achieve satisfactory nitrogen removal effects by regulating single influential factor. However, it provided a possible new way for sediment nitrogen pollution evaluation and regulation.