太湖生态与环境若干问题的研究进展及其展望

Progress and prospect on the eco-environmental research of Lake Taihu

本文着重就太湖水动力及其生态环境效应、太湖沉积物及其内源污染问题和太湖生态系统结构与功能及其蓝藻水华等热点问题近十年来的研究进展进行了回顾.在水动力及其生态环境效应方面,初步摸索出一套适合太湖这样大型浅水湖泊的研究方法,即通过沉积物悬浮过程的研究,把风浪与水体光照透明度、内源释放、水土界面的氧化还原环境等过程和要素联系起来.获得了太湖理化要素随深度变化的内部结构特征,确立了三维水动力模拟模型在太湖应用中的必要性.建立了太湖光照和透明度与悬浮物的关系,及基于悬浮物浓度的太湖初级生产力计算模型.在太湖沉积物与内源污染问题上,初步弄清了太湖沉积物分布与污染物质分布的特征,太湖沉积物悬浮的动力作用的来源与大小.太湖水动力对内源释放的影响,进一步提出了适于太湖内源污染控制的判断方法.对于太湖生态系统结构与功能及其蓝藻水华问题,在蓝藻水华爆发过程假设的基础上,进一步通过营养盐阈值、休眠孢子复苏等方面对此进行了完善.研究还发现了富营养化导致生态系统退化,生物趋于小型化且多样性下降的现象,营养盐循环速率加快,加重水体富营养化程度.进一步通过附着生物的研究,揭示了富营养化导致草型生态系统向藻型生态系统转化的原因.在此基础上,提出了生态恢复应该首先降低营养盐负荷、其次才是生态恢复的新观念,以及湖泊治理必须先控源截污、后生态恢复的新思路.最后,就这几个方面的进一步发展做出了展望.

This paper reviews three hot topics associated with Lake Taihu environmental and ecological researches in the recent ten years, i.e. hydrodynamics and its effects on the lake environment and ecosystem, lake sediment and internal pollution Ioadings, lake ecological structure and functions related to algal bloom. In the aspect of hydrodynamics and its effects, a field approach to investigate the relationships between hydrodynamic parameters and environmental factors was developed. We found hydrodynamical intensity quantitatively related to sediment erosion and suspension, and further related to the transparency, internal loading and oxidation-deoxidization conditions at water-sediment interface. The internal structure of hydrodynamics in Lake Taihu has been achieved, so that the necessity of three dimensional hydrodynamic model has been built instead of two-dimensional hydrodynamic model for this large shallow lake. Relation functions of light penetration and intensity distribution as well as transparency related to seston have been established. Primary production estimate model of Lake Taihu based on the seston has been developed. In aspect of sediment and internal loading, the distributions of sediment and the pollutant in sediment have been clearly revealed. The main force which makes sediment resuspension was identified. The effects of hydrodynamics on the sediment resuspension and further on the nutrient releasing were investigated. A conceptual mode of nutrient releasing for large shallow lake was proposed and the criteria for internal loading control were put forward. In aspect of lake ecosystem and algal bloom, based the hypothesis of algal bloom formation, the understanding of algal bloom formation has been improved via the findings of nutrient thresholds and restoration of dormancy algal spores. Investigations also revealed the phenomena that eutrophication leads to degradation of ecosystem and biota tends to small sizes. The nutrient cycling will speed up and more available nutrient will be imported which in turn enhances the eutrophicating. After investigation of periphyte effects on the submerged macrophyte, the mechanism on macrophyte disappearance was clarified. Based on these findings, new idea on eutrophic lake control and ecosystem restoration was proposed, i.e. reducing the nutrient loading firstly and restoring ecosystem secondarily. Finally, the paper made perspective for the future development of these aspects.