长江中游典型湖泊生态修复参考目标及其生态环境演化研究

Ecological deterioration of lakes is one of global environmental issues. Palaeoecology method is recognized as one of the most effective ways to identify deviations of lakes’ status from pristine condition, and further to establish restoration targets for shallow lakes. As one of the most important functional groups in freshwater ecosystems, chironomids are useful on assessing water quality and reconstructing past ecological status. This study selects the middle reach of Yangtze River, a typical region with numerous lakes, as interested area, and uses fossil chironomids as an indicator of lake’s eutrophciation processes of 10 lakes in Jianghan lake group. The chironomids are analyzed through top-bottom approach, which aims to describe the lakes’ current states and establish reference conditions for restoration. Meanwhile the study will assess the deviation of lakes’ status from pristine conditions. Sedimentary multiproxy and historical archives are colleted from three typical lakes (i.e. Liangzi Lake, Taibai Lake and Donghu Lake), which are dominated by macrophyte or pelagic algal. These data are analyzed for distinguish the relative importance of multi-stressors using the method of multivariate analyses, in order to track the causes of environmental changes in these lakes. The driving forces are detected to obtain the mechanisms of lakes’ response to multi-stressors. This study will integrate the regional information of ecological changes, and provide the reference for lake’s restoration and theoretical basis for ecological environment protection for lakes in the middle reach of the Yangtze River.

湖泊生态环境退化是全球范围内普遍存在的环境问题，古生态学是判识湖泊偏离原始状态幅度进而确定浅水湖泊生态修复参考目标最为有效的途径之一。摇蚊作为淡水环境中最为重要的功能群之一，其群落结构能有效评估湖泊水质状况及生态环境演化过程。本研究选择湖泊集中发育且富营养化突出的长江中游地区，对江汉湖群10个不同营养水平湖泊沉积钻孔,利用顶-底法判识人类活动干扰前后湖泊摇蚊群落变化，以期快速确定区域内浅水湖泊基准环境及湖泊偏离原始状态的程度。基于三个典型湖泊（梁子湖、太白湖和东湖）的沉积序列和流域历史资料，利用多元统计分析方法，揭示多胁迫因子对其生态环境演化贡献份额，初步揭示多重胁迫下湖泊生态环境演化机理。本研究将有利于区域生态演化信息的融合，为长江中游地区系列湖泊生态修复目标的确立提供充实的古生态佐证和理论依据。

长江中游地区湖泊众多，但富营养化问题异常突出。多数湖泊严重偏离其系统“原始状态”，而气候变化和人为干扰是造成湖泊系统状态改变的两大驱动力。本研究对长江中游地区10个不同类型湖泊干扰前后摇蚊、硅藻等生物群落组成进行分析，从古生态学角度揭示湖泊偏离原始状态程度。结果表明：现代环境下生物群落组成均较参考环境发生了明显变化，太白湖、沙湖、严西湖、三里七湖、东湖和网湖中摇蚊优势属种由参考环境下的中营养种或喜植被属种转变为耐营养、耐污种，龙感湖、斧头湖和洪湖中参考环境下的中营养种则被现代环境中喜植被属种替代，三里七湖和太白湖硅藻群落也由指示水动力条件的Aulacoseira granulate转变为耐污种Nitzschia palea，说明人为干扰使得各湖泊均偏离“原始状态”，但偏离程度和方向有所不同。利用生物代用指标结合地球化学指标对太白湖、斧头湖和沙湖历史时期生态环境演化及驱动过程进行分析。结果表明，1940s开始，太白湖营养盐浓度急剧增加，50μg/L TP可作为太白湖生态修复的营养背景值，而～80-110μg/L TP 可能是太白湖由草型湖转变为藻型湖的营养阈值。斧头湖多指标分析结果则强调了大型水利工程建设对湖泊环境的重要影响。闸坝的建成无疑改变了江湖水力连通条件，使湖泊水体营养富集程度有所增加，但同时也刺激了水生植被大量发育，这对湖泊稳态的转换具有重要的缓冲作用。作为城市湖泊，沙湖富营养化滞后于市郊的严西湖，说明工业和生活污水对淡水水质影响深刻，但农业污染物输入却更易在短时间内引起水体富营养化。本研究不仅能为长江中游地区湖泊水体修复提供参考环境，且强调了各类人为活动在短时间尺度上对湖泊生态系统运行机制的重要影响，为决策者各项决策的实施提供有价值的古生态学证据。