鄱阳湖浮游甲壳动物群落结构特征

鄱阳湖是中国第一大淡水湖,具有"丰水为湖,枯水为河"的独特特点。为探讨鄱阳湖浮游甲壳动物群落结构及其时空分布的特征,于2009年全年采集其不同季节、不同水位期的浮游甲壳动物样品进行定量分析。结果显示,鄱阳湖浮游甲壳动物群落结构总体与河流浮游甲壳群落具有相似性。无节幼体、象鼻溞、剑水蚤等河流优势类群在鄱阳湖浮游甲壳动物中占优势;而哲水蚤和溞属仅在低水位季节占优势,枝角类丰度仅在高温、高水位、流速缓的季节高过桡足类。丰水期浮游甲壳动物平均丰度和生物量远远高于枯水期,可达枯水期的50倍,差异极其显著(P0.01)。温度和水位变化引起的环境因子改变是导致鄱阳湖浮游甲壳动物发生季节演替的主要原因;而营养盐对浮游甲壳动物的影响并不显著。空间上浮游甲壳动物群落构成明显不同,年均丰度最高和最低的点均出现在河口地区。因此:对于换水周期短,水交换速率快的水体,应该充分考虑水文条件对生物的影响。

Spatial and temporal distribution characteristics of planktonic crustaceans in Lake Poyang

Poyang Lake, the largest freshwater lake in China, has a large water surface only during wet seasons. However, for most time of the year, about nine months, Poyang Lake is more like a riverine rather than a lacustrine ecosystem, with short water residence time, rapid flows, high suspended solid concentrations, and low water transparences. Considerable studies have focused on the role of trophic state by defining the spatial and temporal distributions of zooplankton, but few studies have investigated the habitat types according to different hydrological states. The above mentioned riverine characteristics are known to have a negative impact on plankton abundance and are responsible for the low plankton standing crops. In this study, we investigated the community structure and seasonal succession pattern of crustacean zooplankton in Lake Poyang and their correlation to various environmental factors. Our findings suggested that planktonic crustacean community structure in Poyang Lake was remarkably similar to that in a river ecosystem. Nauplii, Bosmina spp., and cyclops that usually dominant riverine habitats were found in Poyang Lake. Nauplii, copepodites, calanoids, cyclops, Bosmina spp., and Daphnia could be found throughout the year. The remaining species (normally thermophilic) could only be observed during certain seasons, for example, Diaphanosoma spp. was only found in summer and autumn. The abundance of cladocerans was higher than that of copepods only in the seasons with high water levels and high water temperature and slow velocity. The average abundance and biomass of planktonic crustaceans varied significantly (P < 0.01) between the high-water-level season and low-water-level season. The crustacean abundance in the wet season was 50 times higher than that during the dry season.Natural lakes, reservoirs, and rivers are three diverse ecological systems according to their hydrologic characteristics. Their water retention time and flow velocity are markedly different from each other. Limnological and hydrological factors were compared among these ecological systems to analyze their influences on the distribution and abundance of planktonic crustaceans. Seasonal succession of crustaceans is mainly controlled by water temperature and environmental factors that are influenced by water level. The densities of most zooplankton species are positively correlated with water temperature and chlorophyll-a concentrations. However, nutrients seemed to have a negative effect on planktonic crustacean assemblage in Poyang Lake, which was similar to that in riverine habitats other than lentic lakes. We found a close relationship between community structure and habitat types, as has been reported by many other studies. Therefore, crustacean abundances in Poyang Lake varied consistently with water temperature and water level, but oppositely with nutrients. Owing to the complex hydrologic and water quality situations, the highest and lowest average abundances of planktonic crustaceans spatially appeared in the estuary zone. Therefore, we suggest that, for rapid water exchanging water bodies, hydrologic factors should be considered adequately.