Study On The Release Laws Of Phosphorous And Nitrogen From The Sediment In Dredged Lake, Nanhu

With the development of industry and agriculture, the urban shallow lake in our country is seriously polluted in recent years. Recent study showed that eutrophication in lakes caused by the nutritive matter releasing from sediments.We studied on the phosphorus and nitrogen releasing from the dredged sediments of Nanhu in Nanjing. We used the method of doing experiments outside our lab and monitoring in the lake for getting some results and suggestions about ecosystem reconstruction of Nanhu area. The experiments showed that content of phosphorus and nitrogen in the dredged sediments was high yet, especially content of nitrogen. We can see that dredging reduces the quantity of TP and TN, but not content. We knew the distribution of TP and TN by measuring in horizontal direction and vertical direction, and we estimated the quantity of TP and TN in Nanhu by method of linear interpolation.We studied the regular of TN and TP releasing from sediments with different water (distilled water and water supply) in our experiments. The concentration of TN and TP was raised up rapidly at the beginning of our experiment, then reduced, at last stabilized. The release rate of TP was 34.12mg/m~2.d, and the release rate of TN was 487mg/m~2.d in distilled water, but the rate of TP was 18.36mg/m~2 .d, and the rate of TN was 258mg/m~2 .d in water supply, which showed that something in water supply can restrain the releasing of TP and TN, such as residual chlorine. TN and TP increased rapidly with shaking up water at first, the release rate of TP was 37.41mg/m~2.d, and the release rate of TN was 441mg/m~2.d, then reduced, last stabilized too.Besides we studied 4 kinds of aquatic flowers and 1 type of submerged plant. They can make water clean, especially canna, water bamboo. TP was 0.01 mg/L and 0.02 mg/L, and TN was 0.33 mg/L and 0.23 mg/L in water with canna and water bamboo respectively.In monitoring, we found that TN, TP and COD were releasing from sediments quickly after changing the water. The water quality was inferior to the water standard in our country, even after lake dredged and water changed. We found that the trends were similar in the beginning between the experiments outside our lab and on spot. With the time passing, the trends were more and more different.