鄱阳湖枯水期沉积物磷释放特征及对水位变化响应

通过研究鄱阳湖枯水期不同高程沉积物磷释放热力学和动力学特征,试图建立沉积物磷释放与水位间响应关系,进一步揭示由于江湖关系变化导致的水位下降对鄱阳湖沉积物磷释放风险影响.结果表明:(1)鄱阳湖沉积物高程越高,即出露时间越长,中部和"五河"尾闾区沉积物EC0、DTP、DOP和SRP最大释放量及初始释放速率(0~5 min释放速率)越大,而北部湖区因采砂活动等影响,变化不明显.(2)鄱阳湖水位的持续下降引起的沉积物出露时间延长和出露面积增加,导致全湖沉积物DTP、DOP和SRP最大释放量分别增加了91、81和34 t,虽然该增加量对全湖磷负荷贡献较小(占外源P输入负荷的4.1%、3.7%和1.5%),但"五河"尾闾区沉积物磷释放增加强度为全湖平均值的3倍,意味着随江湖关系的持续变化,来年丰水期鄱阳湖沉积物磷将会集中释放,尤其是"五河"尾闾区等重点敏感区域,其沉积物磷释放量的增加将进一步加大鄱阳湖局部湖区水质下降风险.

Characteristics of phosphorus release in sediment and its response to the change of water level in Poyang Lake in dry season

The thermodynamics and kinetics of sediment phosphorus release at different elevation in dry season from Poyang Lake were studied, to establish the relationship between the phosphorus release characteristics and water level, and to reveal the influence of water level decline on the phosphorus release-risk in Poyang Lake sediments. Results showed that with the increase of sediments elevation, the adsorption/desorption equilibrium concentrations (EC₀), the maximal release potential and the initial release rate (the release rate during 0~5 min) of DTP, DOP and SRP showed increased trend in central and "Five river fringes" areas, whereas showed no obvious trend in northern area due to intense human activities. The amount of DTP, DOP and SRP would increase 91, 81 and 34 ton every year due to the considerable expanded of sediment exposure time and area since 2003, although the increase only accounted for 4.1%, 3.7% and 1.5% of the exogenous P loading, the increment of P relase in "Five river fringes" area was almost three times higher than the average level of the lakes. With the continued change of River-Lake relationship, in the next wet season, a large amount of phosphorus in sediment would release to the overlying water in a short time. The increase of phosphorus release will lead to a greater threat to the water quality in some area, such as the "Five river fringes" area.