基于寒区湖泊冰封期污染物归趋特征的冰冻浓缩乌梁素海水生态环境修复试验研究

Abstract：This project is proposed based on the research results on eutrophication in the Lake Wuliangsuhai over the past ten years. The results showed that the distribution, fate and transport of the contaminants between the ice cover, water body, and the sediment in the lake had some typical characteristics in the winter. In the winter, the contaminants in the lake gradually gathered to the water body under the ice cover during the frozen processes. This resulted that the concentrations and load of the contaminants in the water body are far higher than that in the ice cover. As a result of this, most of the contaminants finally concentrated in the water body under the ice cover when the ice cover reached the maximum thickness. Meanwhile, the volume of the ice cover could be close to or even greater than that of the water body. This implied that "Frozen Concentration" (FR) could be introduced as one of the new restoration technologies, using to remove the contaminants form the lake. To this objective, both the lab and field restoration tests is designed to model the contaminant transport processes in ice, water and sediment in order to get better understanding in the distribution and transport pattern of the contaminants, to replace the high concentrated water body from the "Frozen Concentration" test pond to the constructed wetlands, and to purify the high concentrated water in the constructed wetlands. As a result of this, the results would be used to the lake restoration in the cold zones.

湖泊水污染和水质恶化不仅直接影响其自身水生态环境功能，同时也会在一定程度上引发区域生态环境问题，目前，乌梁素海富营养化广泛受到了学术界和社会的关注。本项目是在长期对乌梁素水环境研究积累的基础上，针对寒区浅水湖泊污染物时空分布的变异性，提出“冰冻浓缩”结合人工湿地修复乌梁素海水生态环境的试验研究。监测和研究结果显示，乌梁素海湖水在冬季结冰过程中，湖水中的污染物在“冷冻浓缩”作用的驱使下，逐渐向冰下水体汇集，致使冰下水体中污染物负荷和浓度远高于冰体中污染物的负荷和浓度，基于这一污染物归趋规律，项目拟通过室内外试验，构建污染物多介质迁移转化模拟模型，揭示污染物在冰-水体-底泥介质间的迁移转化和归趋机理；通过排出“冰冻浓缩”区冰下浓缩水注入至人工湿地的方法，移除和净化湖区水质，从而探索寒区浅水湖泊污染修复的新途径和技术工艺，为乌梁素海综合治理乃至寒区浅水湖泊水生态环境修复提供理论和技术依据。

基于对乌梁素海水环境长期的研究积累，考虑寒区湖泊冰封期覆冰条件下的污染物归趋特征，结合人工湿地修复水环境从而移除和净化湖区水质，对寒区浅水湖泊综合治理及水生态环境修复具有重要意义。本项目在获得资助后，严格按照计划实施，研究内容有：①冷冻浓缩法去除乌梁素海水体污染物的室内研究；②冰封期乌梁素海氮、磷和盐分在水-沉积物界面的分布及迁移特征；③乌梁素海结冰过程中污染物迁移机理；④人工湿地基质筛选及去除寒区湖泊氮磷效果研究。已完成各项研究工作，得到的重要成果如下：①最优的冷冻温度为-15℃，在-15℃冷冻条件下，冰层的结冰厚度为3～11cm，且随着冰层厚度的增加，污染物的去除率呈现先减小后增大再减小的变化趋势；②最佳的受冷面积与水深比值为9.4；③乌梁素海冰封期表层沉积物间隙水NH4+-N浓度较大，表明乌梁素海内源NH4+-N存在从间隙水向冰下水体释放的潜在趋势，乌梁素海冰封期沉积物总体上表现为NH4+-N的“源”；④冰封期乌梁素海水体中盐分的增加打破了盐分在水-沉积物间的动态平衡，在此期间盐分从冰下水体向间隙水扩散迁移，冰封期沉积物呈现为盐分的“汇”；⑤在冰生长过程，约有80%的TDS由冰层迁移至水层；在冰下水体内部，在浓度差的作用下，TDS由冰-水界面向整个水柱迁移直至水体的TDS达到平衡；在水和沉积物之间，约有16.78%的TDS由水体迁移至沉积物；冰-水界面和水-沉积物界面TDS的迁移通量与冰生长率之间呈较好的线性正相关关系。⑥在处理温度较低、浓度较低的含氨氮水体时使用粒径中等（2-4mm）的组合基质效果最好，在处理温度较高、进水浓度较低的含磷水体时使用粒径小（1-2mm）的组合基质效果最好；⑦冷冻浓缩方法和吸附柱结合后氨去除率氮为26%，总磷的去除率为30%。项目的研究意义在于探索旱区浅水湖泊水环境修复的新技术，为湖泊的综合治理和净化水质提供理论和技术依据