Abstract
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.
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