Study On Nitrogen And Phosphorus Release Fluxes Of Sediment-water Interface In Dutang Reservoir

This is a study on nitrogen and phosphorus load in sediment, the influencing factors and the release flux in sediment-water interface of Dutang Reservoir in nomoral season, wet season and dry season of 2009 by combining the method of the field monitoring and laboratory simulation experiment. The results show that the load of total nitrogen ranges from 619.64μg/g to 2950.38μg/g, the load of ammnia ranges from 44.64μg/g to 235.61μg/g, organic nitrogen is the chief constituent of total nitrogen in sediment. The load of total phosphorus ranges from 214.69μg/g to 292.81μg/g. Organic phosphorus in sediments accounted for 50%, while the iron/aluminum phosphorus is the chief constituent of inorganic phosphorus. Iron/aluminum phosphate and organic phosphorus is more than 87% of total phosphorus. It suggests that Dutang reservoir has a large potential to release phosphorus. Contents of total nitrogen and total phosphorus in sediment gradually increase with the flow direction in the same season. While the highest content of nitrogen and phosphorus is in the wet season, and then the normal season, the lowest content is in the dry season. The contribution rate in dry season and normal season is higher than wet season. Laboratory aerobic-anaerobic experiment shows that micro-organisms within the sediment plays an important role in the release of nitrogen and phosphorus.The release of ammonia and nitrate is mainly through diffusion under concentration gradient force and it attains balance quickly in sterilization group. The release of ammonia and nitrate is influenced by the dissolved oxygen concentration in the non-sterilization group. Hypoxia would promote denitrification and the release of ammonia. Sediment phosphorus release to the overlying water by the decomposition of organic phosphate and solution of loosely sorbed phosphiorus in aerobic conditions. While in the anaerobic conditions, microbe would reduce the iron in sediment and then promote the release of phosphorus. It also supports the result by analysising the change of nitrogen and phosphorus content in sediment before and after culture. While it is the further evidence that organic nitrogen, organic phosphorus and iron/aluminum phosphate are likely to release from sediment. According to pore water diffusion model method, the release rate of ammonia from sediment to water ranges from 39.92 mg(m2d)-1 to 118.01 mg(m2d)"', the release rate of DIP (dissolved inorganic phosphorus) ranges from 0.66 d)-1 to 1.63 mg(m2d)-1.However, laboratory culture shows that the release rate of ammonia ranges from 42.39 mg(m2d)-1 to 127.57 mg(m2d)-1, the release rate of DIP ranges from 0.80 mg(m2d)-1 to 2.37 mg(m2d)-1.Moreover, it also shows that the organic nitrogen, organic phosphorus and iron/aluminum phosphorus of sediment at Dutang reservoir are the chief contents to release. There are 23.95 tons ammonia and 0.43 tons DIP release from sediment to water every year. The average contribution rate of ammonia release from sediment to water is 21.01%, while the average contribution rate of DIP is 6.79%.