鲥鯸淀浮游动物群落特征及水质评价

为掌握白洋淀典型湖泊鲥鯸淀浮游动物群落结构及水体营养状况,于2018年秋季、2019年春季和夏季对该淀的浮游动物群落组成、密度、生物量和多样性进行调查研究,分析了主要水质理化指标,运用多变量统计方法分析浮游动群落结构与主要环境因子关系。共鉴定浮游动物3类52种,其中轮虫类种类数最多,为33种,占64.46%。共鉴定优势种23种,其中15个优势种为轮虫;浮游动物密度秋季最高,生物量夏季最高。冗余分析表明,氨氮、COD和总磷是轮虫群落分布的主要影响因子。综合多样性指数与水质指标评估鲥鯸淀水域处于中度污染状态。研究可为白洋淀生境保护和渔业资源的可持续利用提供科学依据。

THE CHARACTERISTICS OF ZOOPLANKTON COMMUNITY AND WATER QUALITY IN THE SHIHOUDIAN LAKE

Shihoudian Lake, located in Hebei Province, China, is one of the main lakes in Baiyangdian Lake, which is the largest shallow lake on the North China Plain and has an average water depth of 2—3 m. With the construction of the Xiong’an New Area, water quality and eutrophication of Baiyangdian Lake have drawn more and more attention from the government and researchers. Zooplankton, as a secondary producer, plays an important role in aquatic food web ecosystem, and is a sensitive environmental indicator of water quality in lakes. In this study, to understand the zooplankton status and the eutrophication conditions of Shihoudian Lake, five sampling sites (A, B, C, D, and E) were established across the lake. Sampling was carried out during six periods, i.e. in the autumn of 2018 (October and November), the spring of 2019 (April and May), and the summer of 2019 (June and July). No sampling was conducted in winter due to the presence of ice on the lake with a depth of 0.5 m. We investigated the community structure of zooplankton in the lake, including species composition, abundance and index of biological diversity. The main physical and chemical factors of water quality were analyzed at the same time. Multivariate statistical approach was used to explore the relationship between planktonic community structure and main environmental variables. 　　The results showed that the spatial and seasonal fluctuation of major water quality parameters was evident in the lake, i.e. chemical oxygen demand in the range of 2.60—9.40 mg/L, ammonia nitrogen of 0.15—1.24 mg/L, total phosphorus of 0.01—0.08 mg/L, total nitrogen of 0.44—2.35 mg/L, nitrate nitrogen of 0.11—0.35 mg/L, nitrite nitrogen of 0—0.01 mg/L, and dissolved oxygen of 6.93—11.43 mg/L. A total of 52 zooplankton species from rotifers, copepod and cladoceran were identified. The zooplankton community structure was dominated by rotifera, which accounted for 64.46% of the species. Twenty-three dominant zooplankton species were further identified, including 15 dominant rotifer species. Specifically, the dominant species were as follows: Keratella cochlearis, Keratella valga, Brachionus angularis, Anuraeopsis fissa, Polyarthra trigla, Filinia longiseta, Trichocerca lophoessa, Trichocerca longiseta, Trichocerca pusilla, Diurella stylata, Diurella insignis, Asplanchna sp., Lecane ungulate, Brachionus angularis, Trichocerca rattus, Bosmina coregoni, Diaphanosoma brachyurum, Thermocyclops brevifurcatus, Mesocyclops leuckarti, Microcyclops vaticans, Thermocyclops hyalinus, Macrocyclops albidus, Cyclops strenuuss. The species number in the seasons was in the order of summer>autumn>spring, the average density was in the order of autumn>summer>spring, while the average biomass was in the order of summer>spring>autumn. The average density of zooplankton varied seasonally in the range of 867—1534 ind./L with a medium value of 1124 ind./L, and the average biomass in the range of 1.16—2.66 mg/L with a medium value of 1.78 mg/L. On the other hand, the spatial variations in the average density and biomass of zooplankton were insignificant. The highest annual average density appeared at sampling site D (1308 ind./L), and the highest annual average biomass appeared at sampling site C (2.43 mg/L). The Shannon-Wiener diversity index in the three seasons was in the range of 1.29—2.23 with an annual average of 1.77, the Simpson abundance index in the range of 0.56—0.84 with an annual average of 0.72, the Pielou evenness index in the range of 0.37—0.61 with an annual average of 0.49, and the Margalef abundance index in the range of 3.64—4.14 with an annual average of 3.84. The redundancy analysis indicated that ammonia nitrogen, total phosphorus and chemical oxygen demand were the main influencing factors on the distribution of rotifer communities. The relationships of dominant species and water quality parameters were as follows: Diurella stylata were positively correlated with ammonia nitrogen and total phosphorus, Anuraeopsis fissa positively correlated with ammonia nitrogen and chemical oxygen demand, Trichocerca longiseta positively correlated with total nitrogen and ammonia nitrogen, Keratella cochlearis positively correlated with pH and dissolved oxygen, and Diaphanosoma brachyurum, Thermocyclops brevifurcatus and Mesocyclops leuckarti positively correlated with nitrite nitrogen. The comprehensive lake evaluation was implemented by analyzing the relationship between the diversity index and the degree of water pollution, and the results indicated that the Shihoudian Lake classifies as mildly to severely polluted. According to the water quality evaluation standards of the water environment for groundwater (GB 3838—2002), the overall status of Shihoudian Lake was between categories Ⅳ and Ⅴ. According to the water quality and zooplankton community structure of the lake, the restoration of Baiyangdian Lake ecosystem requires the regulation of water quality and the increase of biodiversity. Especially for the improvement of fish biodiversity, it is necessary to put forward the classical and non-classical bio-manipulation strategies based on the plankton biomass, carry out the construction of fish habitat, and optimize the structure of food web to construct a complex and stable lake ecosystem.