过去200年来洞庭湖藻类群落演替与驱动因素分析

Algae constitute one of the main groups of primary producers in the shallow lake ecosystems, and the characteristics of algal community structure are closely related to environmental changes. Sedimentary pigments carry information on the history of most algae in water column, and they are useful proxies for inferring past environmental changes. Dongting Lake, a typical lake in the middle and lower reaches of the Yangtze River, is selected as the study area. Pigments in water column and sediment in the lake are analyzed by the method of high-performance liquid chromatography (HPLC). By analyzing the differences of pigments content in water column and surface sediment, this study assesses the preservation status and indicative meanings of sedimentary pigments. Historic algal community succession during the last 200 years is reconstructed based on pigments in short sediment cores. Combined with sedimentary records and historical data in the Dongting Lake Basin, this study partitions out the effects of nutrient and climate factors on algal community by the method of multivariate statistical analysis. Finally,this study reveals the mechanism of environmental changes of the lake. The results can strength theoretical basis for ecological environment protection of Dongting Lake, and they also provide a practical example for application of sediment pigments in paleolimnology researches in the Yangtze floodplain.

藻类是浅水湖泊生态系统最重要的初级生产者之一，其群落结构特征与湖泊环境变化紧密相关。沉积物色素保存了过去水体中大多数藻类的信息，是反演湖泊环境演化历史的有效代用指标。本研究选择长江中下游地区代表性湖泊-洞庭湖，采用高效液相色谱法分析该湖水体和沉积物中的色素，通过现代监测的水体和表层沉积物中色素含量对比分析，评估沉积物色素的保存状况和指示性意义；根据短岩芯古色素含量变化，反演近200年来藻类群落演替历史；结合沉积物多环境代用指标变化和流域历史资料，采用多元统计分析手段，定量区分营养和气候因子对藻类群落的影响份额，进而揭示环境演化的原因。本研究可为洞庭湖生态环境保护提供理论依据，也可为色素指标在长江中下游地区古湖沼学研究中的应用提供例证。

洞庭湖是长江中游重要的蓄洪湖泊，同时在水源供给、生物多样性保护、渔业生产等方面具有重要意义，已列入国际重要湿地名录。然而，近年来湖泊生态环境发生显著变化，包括水体富营养化，尤其是在三峡大坝运行以后。本研究为揭示洞庭湖生态环境演化轨迹及其原因，在东洞庭湖两处采集了浅孔岩芯（72-40cm），210Pb年代结果表明，平均沉积速率在0.66-1.28cm/yr。两根岩芯沉积物粒度自2003年以来明显粗化，这可能与三峡大坝运行后下游河道侵蚀加剧，粗颗粒物质输入增加相关。同时，沉积物中与长江上游供给相关的元素含量下降（如Sc和Ga），而与流域污染输入相关的元素(如Cu和Pb)则增加。以沉积物色素作为过去藻类群落组成的替代指标，1990年以来色素含量变化与浮游植物监测结果相一致，表明古色素较好地记录了过去水体浮游植物群落演替。建坝前色素含量较低与较强的江湖水体交换相对应，建坝后色素含量显著升高与人为污染输入（如氮磷）和水文调控相关。三峡大坝运行后，江湖水体交换减少，换水周期延长加剧了水体营养富集。本研究结果强调了江湖自由水体交换对湖泊生态系统稳定的重要性，同时为洞庭湖生态环境保护提供了重要背景资料。