冻融过程中湖泊污染物多介质迁移转化规律及机制研究

To lakes frozen for several months each year in cold regions, the pollutants are removed from the thick-ice layer and concentrate in the down water and sediment layers. In the next spring, pollutants will return to the upper-layer and spread to the entire lake following ice melting. The ice media impacts the chemical materials’ transport and transformation in lakes annually and the lake environment succession in long term. Clarifying the mechanism of pollutant transport and transformation mechanism in the multimedia of ice, water, and sediment is the fundamental foundation for studying long-term environment change of lakes. This field experiment will be conducted in Wuliangsuhai Lake and Hulun Lake in Inner Mongolia. Firstly, the distribution of various forms of pollutants in the ice, water, and sediment multimedia will be analyzed with the experiment. Secondly, with the experiment results, a model to simulate pollutant transport through ice-water media will be established based on the theory of energy and substance movement. This model will be further integrated into a currently popular multimedia fugacity model. Based on the modeling work, the major environmental factors impacting pollutant transport among the ice, water, and sediment medias will be extracted. At last, this work could provide optimum time and methods to restore the highly pollutant lakes and is beneficial to assess the impact of freezing and thawing process on the long-term lake succession.

寒区湖泊冰封期长，冰层厚度大，污染物在结冰过程中被排出并浓缩于冰下水层中，随着翌年融化过程又重新向上迁移转化，进而回到整个湖体中。这样，冻融过程中，由于冰介质的增加，对湖泊中物质的迁移、转化甚至环境的演替变化都会产生影响。因此掌握污染物在冰—水—泥多介质中的环境过程，对研究湖泊环境变化机理不容忽略。项目以内蒙古乌梁素海、呼伦湖为研究区，首先，进行冻融条件下湖泊环境特征及污染物在冰、水、泥多介质环境中分异规律研究；然后在此基础上，建立污染物在多介质环境过程的逸度模型。进一步引用能态理论“物质由能量高处向能量低处运动”，建立势梯度作用下污染物多介质中的迁移通量方程，并将其耦合于逸度模型中，综合提取驱使污染物迁移转化的主控因子，从而明确污染物在冰、水、泥多介质环境过程机制及其影响因素；最后，量化评价冻融作用对湖泊环境演化的影响效应，为内陆寒区湖泊环境保护与修复选择最佳时间及最优方法提供科学依据。

寒区湖泊冰封期长达5-7个月，冰层厚度大，冻融作用对湖泊中污染物的迁移、转化都会产生重要影响，与无冻融作用的湖泊有巨大差异。鉴于此本项目以内蒙古典型湖泊为研究区，进行冰封期污染物空间分异规律、污染物多介质迁移转化机制、冻融作用对湖泊环境效应等方面的研究。主要研究结果如下：（1）湖泊水体在自然结冰过程中污染物由冰体向冰下水体中迁移，结冰过程对污染物排出能力强弱依次为盐分>重金属>营养盐。从冰晶结构、冰密度等冰微结构方面研究显示，冰盖密度及气泡含量影响了冰体中污染物分布。（2）通过冷冻实验室的室内模拟，控制不同条件研究冷冻浓缩对污染物的去除效果，在适当的条件下盐分的最高去除率可达到96%，总磷的最高去除率可达到85%，总氮的最高去除率可达到80%。（3）利用改进后的QWASI逸度模型精确地模拟了重金属在各环境介质间的迁移过程及迁移量，冰生长期共有50.7kg汞从冰相迁移至水相当中，同时水相中的汞更易迁移至沉积物中，净迁移速率为2.59kg/d。乌梁素海在湖冰的冻结过程中每年由冰体向冰下水体排出的TP约为33.8万t，TN约为128万t。（4）利用度日法经验模型和—维雪/冰热力学数值模型准确的模拟了湖冰生消过程，通过非动力条件下冰封期水环境营养盐负荷估算模型，量化了冻融作用对寒区湖泊的环境效应，研究结果具有重要的科学意义，可为内陆寒区湖泊的环境保护及治理提供科学依据。