梯级调控作用下汉江中下游生源要素迁移及水华暴发的驱动机制

The construction of a large number of cascade hydraulic projects and sluice stations changes natural hydraulic conditions and transport properties of sediment in rivers, which disturbs the migration, distribution and evolution of biogenic elements (N, P and Si), and exacerbates the eutrophication process. Especially in the middle-lower Hanjiang River, ecological and environmental problems caused by algae bloom in the river become increasingly obvious after 4 cascade reservoirs were built. Therefore, it is urgent to master the migration and transformation mechanisms, the source and distribution characteristics of biogenic elements and the impacts of hydraulic and flow-sediment processes on biogenic elements migration under the control of cascade reservoirs and sluice gate stations. Based on field measurements at typical reaches and laboratory experiments, a coupled model integrated by the hydrodynamic model, sediment model, water quality model and algae bloom model will be developed. The flow-sediment process, urban runoff and non-point source pollution emission mode will be analyzed. Additionally, the morphology, migration and transportation mechanisms and dual cumulative effect mechanism of biogenic elements will be revealed. Furthermore, the driving mechanism of diatom blooms in the middle-lower Hanjiang River will be disclosed. The research results will enrich the theory of diatom bloom mechanism in rivers and provide a theoretical foundation and scientific basis for the prevention and control of algae bloom, to support the ecological environment protection.

河流上众多梯级枢纽及控制闸站的建设，改变了河流自然水力条件，扰乱了原有水沙输移规律，引发河流水体生源要素、迁移模式及演进规律的本质改变，加剧河流水体的富营养化进程。汉江中下游4级水利枢纽落成后，该河段由水华引起的生态环境问题越发突显。当前亟需掌握梯级调控与闸站控制双重作用下的水力-水沙过程、生源要素来源和迁移转化及其对水生态环境恶化作用的驱动机制。本课题拟采用典型河段野外监测、室内实验及数值模拟相结合的方法，以揭示汉江中下游梯级调控下生源要素N、P、Si来源、赋存形态、迁移转化及其正负累积性效应为目标，突出研究汉江中下游梯级调控下来水来沙过程与污染源时空变化及闸站调控的城区径流-面源模式；揭示水体生源要素形态及其在水-沙-水华间的迁移转化规律；构建水-沙-生源要素-水华耦合模型；辨析汉江中下游梯级调控变化下生源要素迁移转化规律及水华暴发的驱动机制，为河流型水华防控提供理论基础和科学依据。

泥沙浓度对磷的吸附影响，表现出“固体浓度效应”。随着时间的推移，泥沙对磷的吸附量呈现“先快后慢再平衡”的现象。随着泥沙浓度的增加，单位质量的泥沙对磷的吸附量减少。但总体对磷的吸附量增加。泥沙颗粒粒径越大，对磷的吸附量越小。随着温度的升高，磷酸盐的吸附量呈现线性增长。中性条件下吸附量达到最小值。.河流水文情势的变化通常是由气候变化、土地利用变化和水利工程建设等相互影响造成的。研究建立汉江中下游流域流域模型，使用水文变化指标（IHA）来分析不同条件下水文情势变化。结果表明：丹江口下泄是汉江中下游流域水文情势变化的主要因素，流域区间汇水的贡献；气候变化是区间流域水文情势变化的主要驱动因素，相比较而言土地利用变化对径流变化的影响较小；梯级水库的建设与运行显著改变了水文情势，导致平均流量普遍下降，极端水文情况减少，水文脉冲频率更高但脉冲时间更短，河流水流形态发生变化。.建立了汉江中下游河流水体的汇水流域，分别建立面源污染模型，创新和完善了富营养化生态动力学模型理论。在此基础上建立汉江藻类生长动力学模型，全面分析了影响藻类生长的主要因素，包括：温度、营养物质、光照、种群竞争、藻类死亡以及沉积。对传统的温度限制模式进行了分析校正。详细阐述了藻类生长的光照限制因子的计算方法。并对藻类利用底泥复苏的机制进行总结。用河流水动力水质-富营养化生态动力学模型，模拟了不同水文情势对汉江中下游水生态环境的影响，分析了水文情势的改变对藻类生长的影响。提出了改善汉江水华的措施和建议。