Study On Hydrostatic Pressure And Dissolved Oxygen Effects On Nitrogen And Organic Matter Cycling And Transformation On The Interface Between Water And Sediment

The endogenous pollution becomes the principal factor which influences source water quality after the extraneous pollution has been effectively eliminated. A lot of work has been done in the phosphorus release from reservoir sediments. So the purpose of this paper is about mechanisms of nitrogen release. The process of pollutants release from sediments is very complex. This study focused on the hydrostatic pressure and dissolved oxygen (DO) effects on nitrogen and organic matter cycling and transformation on the interface between water and sediment. The main results show that:(1) Hydrostatic pressure plays an important role in the pollutants release from the reservoir sediments with great water depth. The results show that hydrostatic pressure can induce production of the enzyme and promote some nutrient substance release such as nitrogen and organic matter. The process of nitrification and denitrification is also enhanced. The quantity of biomass in the overlying water after the experiment increased under high hydrostatic pressure (0.1～1.0MPa). Under different hydrostatic pressure conditions, the pollutants release patterns on the multiphase interface was different. Under the condition of0.9MPa, the endogenous pollution release intensity was higher and the quantity of biomass and enzyme were more than the corresponding value under0.4MPa. Under the condition of0.9MPa pressure, microbes are more adaptable and more active, which promote some nutrient substance release such as nitrogen and organic matter.(2) DO concentration can influence the release process of nitrogen and organic matter. When DO was less than lmg/L, organic nitrogen changed into ammonia, resulting in the ammonia nitrogen increase in overlying water; when DO was2～3mg/L, organic nitrogen also changed into ammonia, but part of the ammonia can be transformed into nitrate nitrogen by nitrifying bacteria. And furthermore, the nitrate nitrogen was changed into nitrogen gas by denitrifying bacteria; When DO was5～6mg/L or saturated state, through nitrification,ammonia was oxidized to nitrate, leading to ammonia concentration decreases and nitrate nitrogen content increased gradually.(3) Under anaerobic conditions, different gases were released going with the nitrogen conversion. And under different temperatures, gas composition was different.Under room temperature (20～27℃),the component of gas product was the CH4and the N2. Their average concentration was45.53%and50.83%. Methanogenesis and denitrification process existed at the same time. Under low temperature (8℃), methane production process was strongly inhibited. Denitrifying bacteria can still use nitrate to product nitrogen gas. The average content was91.73%.