洞庭湖区平水期浮游生物群落结构特征及富营养化现状

Characteristics of plankton community structure and eutrophication status in Dongting Lake in the season with normal water level

为了解洞庭湖区浮游生物群落结构特征及其富营养化现状,于2017年8月对洞庭湖区"三口"、"四水"等来水入湖断面、湖区及出口断面等24个采样点的水质状况和浮游生物群落结构现状进行调查。结果表明:浮游植物共检出6门53属75种,平均藻细胞密度为458.3×104个·L-1,生物量变化范围为0.06~3.64 mg·L-1,平均值为0.92 mg·L-1;洞庭湖以蓝藻、硅藻占优,属于蓝藻-硅藻型湖泊;"三口水系"优势种有颗粒直链藻(Aulacoseira granulata)、科曼小环藻(Cyclotella comensis),"四水水系"优势种有颗粒直链藻、铜绿微囊藻(Microcystis aeruginosa),湖区中优势种有颗粒直链藻、铜绿微囊藻、微小平裂藻(Merismopedia tenuissima)、小席藻(Phormidium tenue);浮游动物共检出4门20属,浮游动物密度变化范围5.0~3.4×103个·L-1,"三口水系"优势属为砂壳虫(Difflugia),"四水水系"优势属为砂壳虫、铃壳虫(Tintinnidium),湖区中优势属为砂壳虫、多肢轮虫(Polyarthra)。用综合营养状态指数、浮游生物Shannon多样性指数和Margalef种类丰富度指数分别评价水体的富营养化程度,均表明洞庭湖水体呈富营养化状态。与太湖、巢湖等淡水湖泊相比,洞庭湖藻细胞密度较小,富营养化程度较浅,但从洞庭湖富营养化的历史变化趋势可以看出,洞庭湖水质状况不容乐观,对洞庭湖生态的治理和修复迫在眉睫。

To evaluate plankton community structure and eutrophication status in Dongting Lake, water quality and the current situation of plankton community structure were investigated inAugust 2017. There were 24 sampling points, which distributed in “Sankou”, “Sishui” and other inflow river cross sections, lake regions and outlet sections. The results showed that phytoplankton in Dongting Lake had a total of 75 species belonging to 53 genera from six phyla. The average algae density was 458.3 × 10^4 cells·L^-1, and average biomass was 0.92 mg·L^-1 （ranging from0.06-3.64 mg·L^-1）. Cyanophyta and Bacillariophytadominated in Dongting Lake, which made the lake a Cyanophyta Bacillariophyta lake.Aulacoseira granulata and Cyclotella comensis were the dominant species in “Sankou” while Aulacoseira granulata and Microcystis aeruginosa dominated in “Sishui”. Aulacoseira granulata, Microcystis aeruginosa, Merismopedia tenuissimaand Phormidium tenue were dominant species in lake regions. In terms of zooplankton, 20 genera from four phyla were identified, with total density from 5.0 to 3.4×10^3 ind·L^-1. Dominant zooplankton varied with “Sankou” （Difflugia）, “Sishui” （Difflugia and Tintinnidium） and lake regions （Difflugia and Polyarthra）. To evaluate the eutrophication level, we used three assessment methods, including comprehensive nutritive index, Shannon index and Margalef index. All indices indicated that the lake was under eutrophication. Compared with other freshwater lakes such as Taihu and Chaohu, Dongting Lake was positioned at the lower trophic level and had relatively lower algal density. However, the trend of historical eutrophication implied that the water quality status in Dongting Lake was not optimistic. As a result, more attention should be paid to water body of Dongting Lake and endeavor on ecological remediation is critically needed.