湖泊生态恢复的关键因子分析

中国是一个多湖泊的国家。由于经济快速发展及湖泊资源不合理的开发利用,中国湖泊的污染问题和生态系统退化相当普遍。特别是由于氮、磷等营养元素的富集造成的水体富营养化,导致蓝藻水华频繁发生,甚至出现了饮用水危机事件。由于缺乏基础理论的指导,中国湖泊富营养化治理曾经走过弯路。在没有实现控源截污的条件下,片面强调生态恢复来净化湖泊水环境,一度成为富营养化湖泊治理的主流思想。实际上,湖泊生态恢复是有条件的,而对这些条件的诊断和分析是开展湖泊生态恢复的前提和基础。通过对太湖水生植物分布及其影响因子分析,确定沉水植物恢复的核心条件是水下光照条件。水下光照条件受富营养水平、悬浮物浓度与水深等因子的影响。只有当一个水域的真光层深度接近水深的情况(比值>0.8),恢复水生植物才有可能。改善水下光照条件,包括降低水深,提高透明度,消除风浪等措施,实际上,都是增加真光层深度与水深的比值。在上述生态恢复条件不具备的情况下,湖泊治理与恢复的工作更多地应该聚焦在控源截污方面。这对中国湖泊污染治理与生态恢复具有普遍的意义。

Key factors affecting lake ecological restoration

China has many lakes. Due to the rapid economic development and inappropriate use of lake resources, water pollution and ecosystem degradation are prevalent in most Chinese lakes, especially that the enrichment of nitrogen, phosphorus and other nutrients results in eutrophication, causing frequent cyanobacterial blooms and drinking water supply crises. Owing to the lack of theoretical basis, restoration of eutrophic lakes in China took a wrong strategy in the past-overemphasizing ecological restoration for improving lake environments without proper source control and effluent diversion in watersheds had been the mainstream approach for restoring eutrophic lakes, despite that ecological restoration of lake ecosystems requires a number of conditions. Diagnosis and analysis of these conditions are the prerequisite and basis for the implementation of lake ecological restoration measures. Based on the analysis of the spatial distribution of submersed plants and influencing factors in Lake Taihu, it is found that the key of restoration of submersed plants is underwater light conditions. Underwater light condition is influenced by trophic level, concentration of suspended solids, and depth of lake water. Only when water euphotic depth is close to the water depth (with the ratio of euphotic depth to water depth>0.8), restoration of aquatic plants (especially submersed macrophyte) would be possible. Measures for improving underwater light conditions, including lowering water depth, increasing transparency, and reducing wind all have the effect of increasing the ratio of euphotic depth to water depth. Without these conditions for ecological restoration, source control and reduction of pollutants entering the lakes should be the primary measure for pollution control and restoration of eutrophic lakes. This finding has practical significance for the pollution control and ecological restoration of Chinese lakes.