巢湖崩岸湖滨基质-水文-生物一体化修复

湖滨带生态修复不是简单的水生植物移种,还必须提供其适于生存的基质、水文等外部物理条件。基质作为水生植被的载体,既需要适宜的柔度,也要求一定的刚度。在巢湖崩岸湖滨综合调查的基础上,系统分析了崩岸湖滨带生态退化的成因,研发了基质、水文、生物一体化修复技术,解决了水生植物在恢复生长时期受基质流失和水力切割影响的问题,为水生植物营造了适宜的水生环境。通过西北岸万年埠湖滨的示范工程建设,取得了良好的治理效果,为巢湖崩岸湖滨的生态修复提供一种生态型的、可工程化实施的技术方法。

Integrated matrix-hydrology-biological remediation technology for bank collapse lakeside zone of Chaohu Lake

Lake Chaohu is one of the five largest freshwater lakes in China. Under normal conditions it covers an area of 760km2 and has a coastline of 184.66km. 88km of this coastline easily collapses. These sections are distributed along the northwestern bank, southeastern bank and the south bank of Lake Chaohu. An average of around 390 acres of land collapses into the lake each year. Bank collapse triggers soil erosion and also causes serious ecological degradation of the shoreline. Currently, submerged and emerged plants have mostly disappeared from the lakeside zone of Lake Chaohu. In addition this degradation of the shoreline has reduced the capacity for the maintenance of biological diversity and eliminating pollution. The dominant wind direction in the Lake Chaohu basin is southwesterly. The northwestern shore of lake thus receives the full force of the prevailing wind, especially during March and April, the period of early growth of aquatic vegetation. At this time, high wind and waves in the lake hamper the survival of submerged and emergent aquatic plants. Ecological restoration of the lakeside zone is thus not simply the transplantation of aquatic plants, but must also provide the matrix for survival of these plants, within the water column and exposed to physical environmental factors. The matrix, as the carrier of aquatic vegetation, needs to be sufficiently flexible to be suitable for aquatic plant growth but must be rigid enough to withstand wave erosion and the lodging of vegetation. Moderate hydrology is undoubtedly an important condition for the survival of aquatic plants, large flow and high wind and waves not only wash away substrate, but also damage aquatic plants, often fatally, during their initial growth. As for aquatic plant transplantation, not only do the species selected need to match the main native species of the site but there must be coincidence in the timing of the growing season of transplanted vegetation. In order to implement ecological restoration for the collapsed northwestern bank Lake Chaohu a holistic approach must be adopted which addresses the three interrelated and interacting aspects: the restoration of removed aquatic vegetation, the shoreline substrate instability and physical factors such as erosion due to water and wind. Thus, to be effective, any restoration project must repair the shore matrix and moderate the effects of physical factors while reintroducing appropriate aquatic vegetation. Reeds are the dominant emergent aquatic plant species in Lake Chaohu and currently flourish along the lake dike. This dominance is reflected by the fact that scattered reed plants still remain on the lake shore even after the bank collapse. A comprehensive survey of the collapsed banks of Lake Chaohu systematically analyzed the causes of ecosystem degradation and an integrated matrix-hydrological-biological remediation methodology was determined. A key feature was that an earth dam must be constructed to dissipate the effects of waves, simultaneously minimizing matrix loss and water damage of plants as well as creating the aquatic environment needed for the recovery and growth of aquatic plants. Meanwhile, the dam is constructed from sediment taken from the lake and thus does not affect the overall water capacity. A pilot project based on this idea was carried out on northwestern shore of Lake Chaohu. This methodology could be implemented for the ecological restoration for the entire collapsed coastline of Lake Chaohu.