Studying on Total Nitrogen Content and Release Characteristics of Ammonium in the Surface Sediment of Erhai Lake

The distribution status and release characteristics of nitrogen were investigated by studying on release kinetics characteristics and release potential ability change of the total nitrogen content and ammonia nitrogen(NH4+-N) for nine sediment samples collected from Erhai Lake.The results indicated that the total nitrogen content in the sediments varied from 2.0844 to 6.5153 g/kg with the mean value of 3.5378 g/kg.The area with the highest total nitrogen is located in the west bank of the north section and the second high area is located in the south part near Dali City.The release kinetics of NH4+-N in the sediment surface was well simulated by the first-order kinetic equation.The greatest amount of the released NH4+-N was between 0.1209 and 0.2810 g/kg.The release process of NH4+-N was mainly occurred within the first five minutes and its amount was accounted for 68%-83% of the greatest amount.After 120 minutes,this release process was gradually reached to its balance.The release potential ability of NH4+-N was between 1.7001 and 3.5879 g/kg,and the release potential ability of NH4+-N reached to the maximum value,when the ratio of water and soil approximately was 2500 ∶1.The total nitrogen content,the release potential ability of NH4+-N and the greatest amount of NH4+-N reached in sediment samples of Erhai Lake were higher than that of the sediments from the lakes in the middle and lower reaches of the Yangtze River region.This result indicated that the sediments from Erhai Lake had a risk of nitrogen release greater than those from the lakes in the middle and lower reaches of the Yangtze River region.