太湖近岸潜流带胶体物质特征及对氨氮迁移转化和交换通量的影响机制

The characteristics of ammonia nitrogen distribution in pore water of the nearshore hyporheic zone of Lake Taihu cannot be completely and reasonably interpreted based on the processes of mineralization, anammox, DNRA and nitrification. It is inferred that the ammonia transport and transformation and exchange with lake water are affected by the characteristics of rich colloidal material in the hyporheic zone. For proving up this problem, the nearshore hyporheic zone of Lake Taihu is selected to study through theoretical analysis, field monitoring, undisturbed sediment core experiments and numerical simulation improvement. The characteristics of colloidal matter in the hyporheic zone in different seasons and its influence mechanism on the transport and transformation of ammonia will be studied, including: (1) investigating the source, composition, temporal and spatial distribution and release/transport characteristics of colloidal material in the hyporheic zone under the interaction of surface water and groundwater; (2) clarifying the effects of weak flow, ion strength and temperature gradient on the characteristics of colloidal substances; (3) announcing the relationship between the distribution of ammonia in the hyporheic zone and the characteristics of colloidal substance release and migration; (4) revealing the influence mechanism of ammonia transport and transformation facilitated by colloid, and the seasonal transition "source-sink" relation of ammonia to lake water; (5) improving the model equations of ammonia transport and transformation facilitated by colloid in porous media; and (6) estimating the seasonal exchange fluxes of ammonia in the hyporheic zone with lake water. The research results will be helpful to understand the characteristics of nitrogen cycling in the hyporheic zone of a large shallow lake and provide scientific basis and technical support for the internal pollution control and integrated water management of Lake Taihu.

太湖近岸潜流带孔隙水中氨氮分布特征无法基于矿化、ANAMMOX、DNRA和硝化等过程完全合理阐释，推测氨氮迁移转化和交换受含量丰富的胶体物质特征影响。为探明这一科学问题，以太湖近岸潜流带为研究对象，通过理论分析、现场监测、原状柱模拟试验和数值模拟改进等方法，针对不同季节潜流带内胶体物质特征及其对氨氮迁移转化的影响机制进行研究，阐明地表水-地下水交互下潜流带中胶体物质来源、组分、时空分布和释放迁移特性；探明弱水流、离子强度和温度梯度等对胶体物质特性的影响；揭示主导潜流带氨氮分布与胶体物质释放迁移特性的关系、胶体物质携带氨氮迁移转化的影响机制及氨氮对湖水的“源-汇”关系和季节转换特征；改进多孔介质中胶体物质携带氨氮迁移转化的方程模式；估算潜流带中氨氮与湖水的季节性交换通量。研究成果将有利于深入了解大型浅水湖泊潜流带中氮素循环特征，为太湖内源污染控制和水体综合治理提供科学依据和技术支持。

本项目基于太湖水体-沉积物胶体物质和氮素分布特征及季节性变化规律，通过室内原状柱试验和现场监测、理论分析、数值模拟等方法手段，阐明了地表水-地下水交互下潜流带中胶体物质来源、组分、时空分布和释放迁移特性，胶体物质主要来源于沉积物自身释放、浮游植物和水生植物残体以及污染沉降，并在潜流带水流作用和风浪扰动作用下产生特有的分布特征，其中近岸潜流带胶体物质同时受到污染排放、浮游植物残体和潜流的多重影响。探明了弱水流、离子强度和温度梯度等对胶体物质特性的影响，潜流和扰动作用有利于胶体物质在水平方向和垂直方向上的重新分布，钠离子和钙离子等不同类型离子及其含量影响了胶体物质在沉积物固相介质上的释放/吸附，从而影响沉积物的孔隙度和水流特征，太湖季节性温度的变化和潜流的瞬时变化特征改变了潜流带中胶体物质的释放和迁移特征，其中西部和北部近岸潜流带中胶体物质主要表现为随潜流向水体释放，而南部近岸潜流带中胶体物质主要表现为向沉积物深度迁移并产生堵塞现象，而东部近岸潜流带的胶体物质则随潜流方向发生季节性变化。揭示了主导潜流带氨氮分布与胶体物质释放迁移特性的关系、胶体物质携带氨氮迁移转化的影响机制及氨氮对湖水的“源-汇”关系和季节转换特征，潜流带中胶体物质的释放和迁移，促进了西部和北部湖区水体-沉积物界面处氨氮的释放和迁移，但由于堵塞作用阻碍了南部湖区近岸潜流带水体-沉积物界面处的氮素（包括氨氮和硝态氮）交换。改进多孔介质中胶体物质携带氨氮迁移转化的方程模式，基于胶体物质在沉积物表面的吸附释放特征改进多孔介质孔隙度结构变化开展了潜流带水流、胶体和氮素的迁移转化模拟；估算潜流带中氨氮与湖水的季节性交换通量，基于构建的沉积物空袭结构特征采用VFlux和Hydrus等模型开展了水流和氮素的界面交换通量模拟。研究成果将有利于深入了解大型浅水湖泊潜流带中氮素循环特征，为太湖内源污染控制和水体综合治理提供科学依据和技术支持。