2022年夏秋连旱对洞庭湖浮游动物群落结构的影响

Effects of Summer and Autumn Drought on Zooplankton Community Structure in Dongting Lake in 2022

分析极端干旱事件对浮游动物群落结构和水生态系统稳定性的影响,为减缓干旱对自然和社会的影响、保障水生态安全提供参考。2022年长江流域遭遇1961年以来最严重的水文气象干旱,根据水位波动特征,在干旱期间8月和9月对洞庭湖6个区域26个监测点位进行了2次采样,比较分析了干旱事件下浮游动物群落结构对环境因子的响应。结果表明,洞庭湖浮游动物共检出4门79种;密度呈现出8月(98个/L)<9月(192个/L),密度占比以桡足类最高,为35.0%,其他依次为轮虫34.3%,枝角类28.6%,原生动物2.1%。Shannon-Wiener指数和Margalef指数均呈现出8月<9月,其中8月各区域具有显著差异,9月变化不明显;群落相似性指数由轻度相似(8月)变为中度相似(9月)。极端干旱造成洞庭湖水系水文连通性降低,外源营养物质输入削弱,加之持续高温,导致浮游动物群落结构同质化,稳定性减弱。RDA分析表明,8月浮游动物关键影响因子为高锰酸盐指数(CODMn)、总磷(TP)、正磷酸盐(PO_(4)^(3-)-P)、溶解性硅酸盐(DSi)和浊度(Turb),9月为总悬浮物固体(TSS)、Turb和硝氮(NO_(3)^(-)-N)。相关性分析表明,浮游动物与氮磷营养盐和水温(WT)显著负相关,WT与氮磷营养盐呈显著正相关,说明浮游动物受WT的直接或间接影响。综合分析表明,极端干旱期间水文连通性和水温是影响浮游动物群落结构的主导因子,保障水文连通性是促进能量流动、物质循环和水生态系统健康的前提条件。

Analyzing the impacts of extreme drought events on zooplankton community structure and aquatic ecosystem stability provides a reference for mitigating the impacts of drought on nature and soci-ety,and safeguarding water ecological security.In 2022,the Yangtze River basin experienced the most se-vere hydro-meteorological drought since complete records were kept in 1961 and it dramatically affected the ecological environment of Dongting Lake basin.In this study,we investigated the effects of the drought on the zooplankton community structure of Dongting Lake and analyzed the response of the zoo-plankton community to the drought.In August and September of 2022,26 sampling sites were set in Dongting Lake based on water level fluctuations.Zooplankton and water samples were collected once each month for analysis of zooplankton and determination of water quality parameters.A total of 79 zoo-plankton species from 4 phyla were collected.Zooplankton density in Dongting Lake was lower in August(98 ind/L)than in September(192 ind/L)and copepods were most common(35.0%),followed by rotifers(34.3%),cladocerans(28.6%)and protozoa(2.1%).The Shannon-Wiener diversity and Margalef richness indices of zooplankton were both lower in August than in September,with significant spatial differences in August,but not in September.Community similarity between different areas was slight in August and moderate in September.Extreme drought decreased hydrological connectivity in Dongting Lake,and de-creased the input of exogenous nutrients.Coupled with persistent high temperatures,this resulted in ho-mogenization of zooplankton community structure and a reduction in stability.Redundancy analysis shows that the key influencing factors of zooplankton were permanganate index(CODMn),total phospho-rus(TP),orthophosphate(PO_(4)^(3-)-P),dissolved silicate(DSi)and turbidity(Turb)in August,and total sus-pended solids(TSS),Turb and NO_(3)^(-)-N in September.Correlation analysis shows that zooplankton had a significant negative correlation with nitrogen,phosphorus and water temperature(WT),and WT had a sig-nificant positive correlation with nitrogen and phosphorus,indicating that zooplankton were directly or in-directly affected by WT.Comprehensive analysis shows that hydrological connectivity and water tempera-ture were the primary factors affecting the zooplankton community structure during the extreme drought,and safeguarding hydrological connectivity is a prerequisite for promoting energy flow,material cycling and aquatic ecosystem health.