沉水植物覆盖下大型浅水湖泊表层沉积物磷库收支对风浪扰动的响应研究

The mechanism of the response of surface sediment resuspension-settlement, phosphorus migration and transformation covered by submerged plants to wind-induced hydrodynamic disturbance is unclear in large shallow lakes. The project takes Lake Taihu which is a large shallow lake as the research object, and combines with various factors such as the modes of various species and distribution density of submerged plants and wind-induced hydrodynamic disturbance, and uses various research methods such as the analysis of sediment cores, in-door hydrodynamic simulation experiments, numerical modeling, and measurement of different phosphorus forms, to research (1) the effects of natural wind-induced hydrodynamic disturbance on sediment resuspension-settlement and phosphorus sedimentation with the condition of the existence of submerged plants and the coverage of various species; (2) the migration mechanism of surface sediment phosphorus covered by submerged plants responding to wind-induced hydrodynamic disturbance; (3) the construction and the performance evaluation of the modelling based on the budgets of surface sediment phosphorus. The results provide the theoretical basis for the assessment and management of surface sediment-phosphorus pool and the physical effects of submerged plants in shallow lakes. The project takes the participation of aquatic plants in the hydrodynamic disturbance into account, to research the effects of wind-induced hydrodynamic disturbance on the migration of different phosphorus forms of surface sediment covered by various species and distribution density of submerged plants, which has obvious features and new conception.

大型浅水湖泊中沉水植被覆盖下表层沉积物再悬浮沉降及其磷组分迁移、转化变率对风浪扰动的响应机制尚不清楚。课题以大型浅水湖泊太湖为研究对象，结合不同种类、分布密度的沉水植物覆盖模式和风浪扰动水动力因素，采用野外沉积柱分析、室内水动力模拟试验、数值模拟手段，利用不同形态磷检测等技术，研究：（1）有无沉水植物存在及不同种类覆盖对表层沉积物再悬浮沉降和磷沉积响应自然风浪扰动的钝化效应；（2）沉水植物覆盖下表层沉积物磷响应风浪扰动的迁移机制；（3）表层沉积物磷库收支模型的构建和效果评估。研究结果可为大型浅水湖泊表层沉积物磷库收支评估、管理和沉水植物的物理行为效应提供理论依据。本项目考量水生植物因子参与水动力扰动的程度，综合研究不同种类和分布密度确定的沉水植物存在模式下表层沉积物各形态磷组分响应风浪扰动的迁移钝化机制，具有明显特色和新意。

大型浅水湖泊水体及沉积物易受风浪扰动作用，影响表层沉积物再悬浮沉降及其磷组分迁移、转化变率，沉水植物覆盖有抗击水动力扰动和固定沉积物的作用，深刻影响着表层沉积物磷再生潜力、埋藏强度。本研究以大型浅水湖泊太湖为研究对象，利用资料分析、野外调查、室内水槽模拟试验、数值计算等手段，对无水草湖心区和沉水植物覆盖的东太湖区域开展了表层沉积物磷迁移的影响研究，探明了风浪扰动下的沉积物再悬浮特征及表层沉积物磷通量变化等。主要研究结果如下：. （1）2009-2018年，太湖流域年际日平均风速变化范围为2.53-2.68 m/s，年际间变化均不大，风速均呈逐年下降趋势，总体上主要以西北风、东南风为主。. （2）太湖沉积物总磷含量为328.75-1688.75 mg/kg，沉积物总磷、无机磷含量均值从大到小依次为苦草区、轮叶黑藻区、马来眼子菜区、湖心无水草区，随深度呈现出先增加后减小的趋势，沉积物年平均磷吸附通量为0.640-0.664 t/a。. （3）随着风浪扰动强度的增加，悬浮物浓度、悬浮物粒径的D50平均值、间隙水TP、上覆水TP浓度均呈增加趋势，苦草对表层沉积物再悬浮释放磷具有相对较强的抑制作用，但强风浪扰动下不同沉水植物覆盖的间隙水、上覆水磷浓度没有显著差异。. （4）2009-2018年湖心区表层沉积物发生再悬浮的天数为152-206天/年，东太湖表层沉积物发生再悬浮的天数为36-81天/年，均呈逐年下降的变化趋势，可根据风速分级判断是否发生表层沉积物再悬浮，表层沉积物再悬浮通量与平均风速呈幂函数拟合关系，2009-2018年近十年太湖表层沉积物再悬浮量为43.46-45.14万t/a，湖心区、东太湖表层沉积物再悬浮的磷释放通量分别为268.26-278.30 t/a、14.82-15.33 t/a。. 本研究考量水生植物因子参与水动力扰动的程度，综合对比分析了无沉水植物及不同沉水植物种类形态模式、分布密度模式下风浪扰动驱动的湖泊底部水动力、沉积物再悬浮及沉积物磷释放的影响，研究结果可为大型浅水湖泊表层沉积物磷库收支评估、管理和沉水植物的物理行为效应提供理论依据。