西洞庭湖沉水植物分布格局对环境因子及水文情势差异的响应

The response of submerged plants to different environmental factors and hydrologic regime in West Lake Dongting

沉水植物是湖泊生态系统的重要组成部分,其生产力和分布格局受环境因子特别是水文情势决定.洞庭湖是长江流域重要的大型通江湖泊,近年来受人为干扰和气候变化影响,水文节律与水质等环境因子发生改变,导致沉水植物出现衰退现象,急需开展科学恢复,因此有必要对洞庭湖沉水植物深入研究.本研究选取西洞庭湖为研究区域,于2018年和2019年夏季调查了12处典型生境、98个样点的沉水植物与水深、透明度等11个环境因子,采用独立样本T检验和冗余分析方法对沉水植物与环境因子的关系进行分析,对比年际水文情势变化的影响.结果表明:1)西洞庭湖沉水植物主要在水深较浅、水质更优、水体更为稳定的半阻隔子湖和自由连通的湖湾区分布,在河道及水位波动较大的区域分布较少,有、无沉水植物分布样点间存在显著差异的环境因子为水深、透明度、底泥总磷和pH;2)在有沉水植物分布的样点,沉水植物生物量与pH、水深和水体总磷呈显著相关关系;3)自然连通的季节性淹没湖泊沉水植物生物量在2018年高于2019年,可能与2019年58月沉水植物关键生长期出现的涨水过程有关,持续的高水位对沉水植物的生长产生了不利影响.维持自然水文节律、湖泊生境异质性与自由连通性、健康的水质等是恢复西洞庭沉水植物的关键,建议在水深低于3 m、营养盐浓度适中、流速及风浪较小的湖湾区或半阻隔湖泊开展沉水植物恢复.

Submerged plants are important components in lake ecosystems,their production and distribution pattern are affected by environmental factors,especially the hydrologic regime.Lake Dongting is an important large lake in the Yangtze River Basin with free hydrologic connection to the main stream.In recent years,due to influences of human disturbances and climate change,environmental factors such as hydrologic regime and water quality of Lake Dongting have been changed dramatically,resulting in the decline of submerged plants,which calls urgent science-based rehabilitation.Thus,there is a need to have further study on submerged plants at Lake Dongting.In this study,West Lake Dongting was selected as the research area.Submerged plant communities and 12 environmental indicators were investigated in 98 sampling plots at 11 sites in West Lake Dongting during summer in 2018 and 2019.Independent t-test and redundancy analysis were used to evaluate the relationship between the submerged plants and environmental factors,and to explore the effects of hydrologic regime change on submerged plants between years.Results showed that:1)Submerged plants in West Lake Dongting were mainly distributed at semi-isolated sub-lakes or free flooding lake bays where with shallower water depth,better water quality and more stable water body,whilst there is less distribution at sites in major flowing channels and with high water fluctuation.Water depth,transparency,total phosphorus in bottom sediment and water pH showed significant differences between sites with and without appearance of submerged plants in West Lake Dongting;2)Biomass of submerged plants was significantly correlated with pH,water depth and total phosphorus in water;3)At free flooding lake bay,biomass of submerged plants was higher in 2018 than it in 2019.It is supposed to be the result of water level raising processes during May to August 2019 when was key growing stage of submerged plants.A continuously high-water level adversely impacted plant growth.Maintaining natural hydrologic regime,habitat heterogeneity with free flow in the lake,and healthy water quality were proposed to be the key factors to rehabilitate submerged plants in the West Lake Dongting.Sites at free flooding lake bay or semi-isolated sub-lakes those with water depth less than 3 meters,appropriate water nutrients,low water flow rate and less waves were recommended to be rehabilitated in priority.