Study on Release Characteristics of Ammonium in the Surface Sediments of Dianchi Lake

Surface sediment samples were collected in 2013 from 36 sites in Dianchi Lake to study the endogenous pollution. The distribution of NH4+-N content in the sediments and the release kinetics status of NH4+-N were researched. The results showed that the content of NH4+-N in the surface sediments was about 155. 8-667. 8 mg/kg,with average content of 333. 7 mg/kg. The maximum content occurred in the center of the lake. Over the 0-5 minute time period,the release rate of NH4+-N was the fastest,being up to 3. 34-42. 31mg/(kg·min). The release rate gradually decreased after 5 minutes and balanced after 120 minutes. The potential release ability of NH4+-N was about 17,147-34,163 mg/kg,which was related to the ratio between water and soil. In most regions of Dianchi Lake,the potential ability of release of NH4+-N was relatively high,especially in the north of Caohai and the Panlong River mouth. Either the release ratio or the potential release ability of NH4+-N in Dianchi Lake was higher than that in the lakes in the middle and lower streams of the Yangtze River. The release ratio in Dianchi Lake was similar to those in Erhai Lake,which is also located on a plateau; however,the potential release ability of NH4+-N in Dianchi Lake was much higher than that in Erhai Lake. Therefore,the release risk of NH4+-N in the surface sediments in the Dianchi Lake was extremely high.