The Release Of Nitrogen And Phosphorus In The Sediment On Different Light And Hydrodynamics Conditions

Nitrogen and Phosphorus is generally considered to be the major growth limiting nutrient in aquatic ecosystems. Studies have shown that in some situations eutrophication can continue even after external anthropogenic sources of phosphorus have stopped. This has led many researchers to examine other causes of eutrophication, including the importance of internal loading of phosphorus released from the sediments. Characteristics of phosphorus and nitrogen dynamics are closely related to sediment and environmental conditions. The previous studies focused physical and factors (dissolved oxygen, pH, temperature, sediment grain size) on the influences of dynamics of N&P on the sediment-water interface, but the research of light and hydrodynamics were less, therefore, it’s necessary to study on the impact of light and hydrodynamics conditions on the dynamics of phosphorus and nitrogen. The achievements of this study can enrich the theory of N&P dynamics. Furthermore, the conclusions of this study can give guides to protection of eutrophication, take control of primary productivity and aquaculture.In this study, Measurement of species of nitrogen and phosphorus concentrations in the sediment cores were made in the laboratory and the sediment samples sampled in the Daya bay were cultivated in different light and water velocities conditions. According to this study, we can get the following conclusions:(1) The sediments in Daya bay have relatively high nitrogen and phosphorus concentrations. This led the sediment can become a potential internal N&P sources for aquatic organism. The linear relationship between kjeldahl nitrogen and total ammonia nitrogen and phosphorus were established showed that kjeldahl nitrogen is direct proportional to ammonia nitrogen and total phosphorus, moreover, the ratio of kjedahl nitrogen to total phosphorus is about11in sediment of Daya Bay. This suggests nitrogen is the main factor of the primary productivity in these sea areas. The dissolved reactive phosphorus (DRP) and ammonia nitrogen annual emission were predicted by the Fick’s first law. The results showed that the DRP and ammonia nitrogen annual emission were very large. (2) Sediments were incubated in different light conditions which was ranged form0w-23w. The results indicated that light conditions had no significant effect on the N&P dynamics on the sediment-water interface. Light only had major impact on fraction of N&P in aquatic ecosystems, and the release of N&P didn’t increase evidently.(3) The water velocities above the sediment-water interface ranged from Ocm/s to0.78cm/s. High fluctuations with high energy dissipation rates were indicators of a turbulent flow at the sediment-water interface. The long-term cultivation results indicate that the average of N mass flux ranges from17.94～20.92(mg/m2/d) under the aerobic condition,25.44～28.52(mg/m2/d) under the normal conditions. The average of P flux were close to zero under the aerobic condition, but it ranged from3.22-16.1(mg/m2/d) under the normal condition. Line fitting correlations analysis between the average N&P mass flux and water velocities showed that the Pearson correlation coefficient was R2>0.98, therefore, Using appropriate fitted equation can describe the relationship between N&P mass flux at the sediment-water interface and water velocities. Dissolved reactive phosphorus(DRP) in the overlying water and its release flux form the sediments were sensitive to the DO concentration in the water column, but nitrogen were insensitive to the DO concentration, DO only have effects on the chemical forms of nitrogen. Under the aerobic conditions, the key factor has effects on the dynamics of N&P is water velocity, but it is velocity and DO under the normal conditions.