Regularity of nitrogen release under low oxygen conditions from various sediments in a river network
低溶解氧状态下河网区不同类型沉积物的氮释放规律

Four sediment samples affected by different human activities were collected from the Wenzhou Wenruitanghe River network, Zhejiang Province. They represented upriver water, tannery drainage, construction waste and municipal drainage. The characteristics of release of various nitrogen (N) forms from the different sediments were investigated under low dissolved oxygen (DO) conditions. The transformation of N in the sediment-water system was significantly affected by the conditions of the overlying water. It was disadvantageous for N release if the overlying water was seriously contaminated, and it was advantageous for N release when the condition of the overlying water was improved. The N in the overlying water, highly contaminated in the Yutianhe River, could be transferred into the seriously polluted sediment by diffusion, leading to an increase of TN and nitrate nitrogen (NO-3-N) in the sediments. Input control of external N could decrease the potential load of contamination. Ammonia nitrogen (NH+4-N) was released into the overlying water from all kinds of sediments while NO-3-N was transferred into them. The quantities of NH+4-N released from sediments were higher than those of NO-3-N transferred into the sediments. The risk of NO-3-N release was lower than that of NH+4-N under low oxygen conditions.