寒区湖泊冰封期藻类和污染物冰-水介质迁移机理及对水华影响研究

Lakes have some typical characteristics in the cold regions, such as, a longer frozen period, thicker ice layer, small flow, and serious pollution. These also showed different geochemical behavior and ecological effects. With the freezing and thawing of lake water, algae and pollutants will be constantly re-distribution in the ice - water medium. The results have a significant impact on the mechanism of lake ecological environment changes. The study area is located in Wuliangsuhai Lake in inner mongolia. Research contents are as follows. Firstly, temporal and spatial variability on algae and pollutants been studied, including different forms of nitrogen, phosphorus, chemical oxygen demand. Response relationship among algae, pollutants and environmental indicators (meteorological factors, water depth, ice temperature, ice thickness, ice pressure, pH, dissolved oxygen, redox potential, conductivity) were revealed. Secondly, the algae and contaminant transfer flux in different ice - water layers were calculated, and using water dynamics, thermodynamics, freeze-thaw effect and energy state theory interpret the mechanism of migration and transformation of algae and contaminants in ice layer, ice - water interface and the water layer. Finally, the characteristics of algal community structure, dominant species and their formation conditions in the frozen period were studied. Based on this, combined with community characteristics of algae and dominant species features in non-frozen period, the "contribution rate" of dominant species of algae in frozen period to outbreak of algae bloom next year was quantified. The purpose of the study is to provide references and scientific basis for management and restoration of lakes in cold regions.

寒区湖泊具有冰封期长，冰层厚，流量小，污染重等典型特点，表现出了不同的地球化学行为和生态效应。藻类和污染物随着湖水冻融过程在冰-水介质中将不断重新分配，分配结果对湖泊生态环境变化机理产生重大影响。项目以内蒙古乌梁素海为研究区域，从以下3方面开展研究。首先，研究冰封期藻类和污染物（不同形态氮、磷和化学需氧量等）的时空异质性，揭示藻类和污染物与环境指标（气象因子、水深、冰温、冰厚、冰压力、酸碱度、溶解氧、氧化还原电位、电导率等）之间的响应关系；其次，计算不同冰-水层藻类和污染物迁移通量，综合水动力学、热力学、冻融效应和能态理论等方法诠释藻类和污染物在冰层、冰-水界面和水层的迁移转化机理；最后，探求冰封期藻类群落结构特征、优势种及其形成条件，并在此基础上结合非冰封期藻类群落特征和优势种特点，量化冰封期藻类优势种对翌年水华的"贡献率"，为寒区湖泊治理和修复提供参考方案和科学依据。

乌梁素海作为我国八大淡水湖之一，地处高纬度地区，有别于其他湖泊。前人相关研究主要集中在湖泊的非冰期。而寒区湖泊具有冰封期长、冰层厚、流量小、污染重等特点，表现出了不同的生态效应和化学行为。污染物随着湖水冻融过程在冰-水介质中将不断重新分配，分配结果对湖泊生态环境变化产生极大影响。因此，本项目以冰封期的乌梁素海为研究对象，从冰体和水体两个不同的角度出发，研究冰封期藻类和污染物的时空异质性，揭示藻类和污染物与环境指标之间的响应关系；计算不同冰-水层藻类和污染物迁移通量，揭示藻类和污染物在冰层、冰-水界面和水层的迁移转化机理；探求冰封期藻类群落结构特征、优势种及其形成条件，分析了非冰封期藻类群落特征和优势种特点。为该方向的研究提供了理论基础。结果如下：（1）冰封期冰—水介质中各形态磷、氮的含量水体全部大于冰体，冰层中的含量大致为表层冰＞冰水界面冰≥中层冰。冰封期冰水介质中COD的含量水体总体大于冰体，COD的含量随着冰厚百分比的增加而增加。（2）冰下水体共检出浮游植物7门32属37种。其中，硅藻门10属12种；绿藻门8属9种；裸藻门4属6种；甲藻门4属4种；蓝藻门3属3种；隐藻门2属2种；褐藻门1属1种。而在冰层中共检出浮游植物7门34属60种，其中，硅藻门16属34种；裸藻门3属8种；绿藻门5属6种；蓝藻门3属5种；甲藻门4属4种；隐藻门2属2种；金藻门1属1种。（3）冰下水体的优势种由硅藻门的大柄链藻、暗色圆筛藻、极小冠盘藻和星形冠盘藻，绿藻门的水溪绿球藻，蓝藻门的细长聚球藻，甲藻门的利马原甲藻、薄甲藻、不显著多甲藻组成，不同采样点的优势种组成有所差距。（4）溶解性总磷，氨氮分别是乌梁素海冰封期冰下水体和冰层的主要污染因子，TP和TN是影响乌梁素海冰封期水体和冰体浮游植物群落分布最主要的环境因子。