Studies On Distribution Of Nutrients And Their Release From Sediment In Dongping Lake

Sediment is the important reservoir of nitrogen, phosphorus and organic matters. When external contaminations are under control, nitrogen, phosphorus and organic matters release from sediment may result in continuous eutrophication of lakes. Dongping Lake is a adjusting and important freshwater lake on the east route of the South-to-North Water Diversion Project, and its water quality has an important influence to the quality of diversion water. However, there is still a lack of information on the distributions of nitrogen, phosphorus and organic matters in sediments of Dongping Lake. Therefore, investigation of the nutrients and organic matter distribution characteristics of the water and surface sediments in Dongping Lake is clearly essential.This study sets Dongping Lake as the research object, and carries out the research of nitrogen, phosphorus and organic matters distribution in both of sediment and overlying water and the phosphorus forms in sediment of Dongping Lake. Then the environmental quality and potential ecological risk were evaluated. The static release of nitrogen, phosphorus and organic matters in sediment were investigated, and the simulation experiments of nitrogen and phosphorus release from sediment were studied in laboratory. The results were as follows:The concentrations of NH4+-N-、TN、 TP and COD in overlying water of Dongping Lake were lower than Grade III of the "China surface water quality standard (GB3838-2002)", and the higher regions were almost in aquiculture areas and residential areas. The horizontal distribution of nutrients and organic matters in sediment of Dongping Lake showed that, the TN and TP concentrations in sediment samples from estuary of Dawen River were higher, probably due to the nitrogen and phosphorus contaminants which were from the river basin. However, the sites of higher OM concentrations were in southwest of Dongping Lake, probably due to the dead plants. The vertical distribution of nutrients and organic matters in sediment of Dongping Lake showed that, the TN and TP concentrations in5～10cm depth sediment samples were highest, and the concentrations of TN, TP and OM were1127.11mg/kg,349.49mg/kg and61947mg/kg, respectively. It showed that the contamination of sediment in Dongping Lake was influenced by human activities.The phosphorus forms in sediment of different depths showed that, the NaOH-P contents were the highest, and IP-P contents were the second highest. As the depth of sediment in Dongping Lake increased, there were no obvious correlations among the different forms of phosphorus. As the results of evaluations showed, phosphorus was most severe enrichment in the sediments at sites around of Lashan Wharf and estuary of Dawen River. The sediment in Dongping Lake was polluted more severe by OM, and most of sediment was around the estuary of Dawen River.The static release of nitrogen, phosphorus and organic matters in sediment of Dongping Lake showed that, the release contents of NH4’-N、TN、SRP、TP and COD were highest at the21、16、21、33and28day, respectively, the contents were0.46-1.03mg/L、1.15～2.15mg/L,0.03～0.23mg/L,0.01～0.15mg/L and18～33mg/L, respectively. The adsorption-desorption experiment showed that, the risk of nutrient release would happen onto sediment-water interface during the exchange of nutrient.In this study, the nutrients and organic matter distribution and release characteristics of the surface sediments in Dongping Lake were investigated and the result can offer scientific information on management of Dongping Lake for local government.