江湖关系变化对鄱阳湖沉积物氨氮释放风险的影响

选取了鄱阳湖北部湖区、“五河”入湖尾闾区、湖心区共14个不同高程的表层出露沉积物样品,通过研究其总氮(TN)含量和氨氮(NH4+-N)释放热力学及动力学特征,试图揭示江湖关系变化导致的水位变化对鄱阳湖沉积物氨氮释放风险的影响.结果表明,鄱阳湖沉积物TN含量在377～3875mg/kg之间;NH4+-N吸附/解吸平衡浓度(EC0)在1.49～2.99mg/L之间;单位沉积物NH4+-N的最大释放量在17.00~140.97mg/kg之间,NH4+-N释放主要集中在0~5min时段,占最大释放量的50.84%~73.34%,TN含量、EC0浓度、NH4+-N的最大释放量及初始释放速率均随沉积物所处高程的增高而增大,由此可见近年来由于长江来水量减少,鄱阳湖与长江之间江湖关系的改变,引起鄱阳湖枯水期提前及低枯水位持续时间增加,导致沉积物出露时间延长,进而促使沉积物TN含量、EC0浓度、单位沉积物NH4+-N最大释放量及0~5min时段NH4+-N释放速率升高,进而引起沉积物NH4+-N释放风险增大,是导致鄱阳湖水质恶化的重要机制之一.如果此江湖关系变化持续,枯水期低枯水位持续,势必引起沉积物出露面积进一步增大及出露时间的延长,最终可导致来年丰水期鄱阳湖沉积物NH4+-N释放风险增大.

The influence of the River-Lake relation changed on the sediments ammonia nitrogen release risk of Poyang Lake

The total nitrogen (TN) contents and thermodynamics/kinetics of ammonia nitrogen (NH4+-N) release characteristics of Poyang Lake surface exposed sediments were studied, tried to reveal the influence of the water level changed resulted from the relationship between Yangtze Rive and the Poyang Lake changed on the NH4+-N release risk of Poyang Lake sediments. The TN contents of Poyang Lake sediments varied from 377to 3875mg/kg; the adsorption/desorption equilibrium concentrations of NH4+-N(EC0)varied from 1.49to 2.99mg/L; the maximal release potential of NH4+-N varied from 17.00to 140.97mg/kg, the NH4+-N release process was mainly occurred within the 0~5minutes that accounted for 50.84% to 73.34% of the release amount, the TN contents, EC0 concentrations, the maximal release potential and the initial release rate of NH4+-N increased with the height increased, that’s dues to the water from Yangtze river keep reducing,resulting in the low water level advanced and the outcropped time prolonged, then caused the TN contents, EC0 concentrations, the maximal release potential and the initial release rate increased, these factors changed were the important mechanism that caused the NH4+-N release risk increased and the deterioration of water quality. With the Poyang Lake water lever keep lower, it’s bound to lead the sediments exposed area and time increased. then caused the increased of NH4+-N release risk of next year.