双向环形水槽模拟变化水位和流速下洞庭湖沉积物氮释放特征

浅水湖泊生态系统中的沉积物—水界面是湖泊内源氮释放的重要界面,而水动力因素是改变沉积物氮释放的重要因素.三峡大坝修建以后,长江中下游通江湖泊的水动力条件发生了明显的变化.通过采集洞庭湖湖口区域的沉积物和水样,在双向环形水槽动力模拟装置内模拟湖泊水位和流速的变化,探讨湖泊沉积物氮在沉积物和水系统中的二次释放特征.结果表明,随着扰动强度的增加,上覆水悬浮物浓度增大,上覆水中总氮浓度增加,沉积物向上覆水释放氮的强度增强,水动力条件的改变所引起的沉积物内源氮释放不容忽视.在该模拟实验条件下,沉积物存在最适扰动水位(20cm),此水位下上覆水中悬浮物浓度最低,总氮浓度最小.水动力条件的改变对上覆水和沉积物—水界面处铵态氮和硝态氮浓度的影响并不明显,孔隙水中铵态氮与硝态氮之间发生形态的转化.

Characteristics of nitrogen release from Lake Dongting sediments under variable water level and velocity in the two-way annular flume

Sediment-water interface is a crucial place for internal nitrogen release in the shallow lake ecosystem and the hydrodynamic factors have significant influence on sediment nitrogen release. After the construction of the Three Gorges Dam, hydrodynamic conditions for shallow lakes in the middle and lower reaches of the Yangtze River have changed apparently. Water and sediments samples collected from Lake Dongting region were used to simulate the release characteristics of nitrogen from sediments under experience conditions of variable water level and velocity. The results showed that as the water level/velocity increased, concentrations of the suspended solids (SS) and total nitrogen (TN) in the overlying water increased and the nitrogen release intensity from sediments to overlying water enhanced. This internal nitrogen release caused by variable hydrodynamic conditions should not be ignored. Under the simulation conditions there was an optimal disturbance water level of 20 cm, where concentrations of the SS and TN were lowest in the water level nearby. The influence of variable water level and velocity on ammonium nitrogen and nitrate nitrogen in the overlying water and sediment-water interface were unapparent, while there was a form transformed between ammonium nitrogen and nitrate nitrogen in the pore water.