Distribution, relationship and significance of phytoplankton, chlorophyll-a and environment variables in spring season of the Zhelin Reservoir, Jiangxi Province

Abstract

江西柘林水库是长江中游的大型峡谷型旅游性水库，库容79.2×10⁸ m³，长115 km.2015年4月在56 km的中心库区走航和定点测量了水库表层水体浮游藻类、叶绿素a（Chl.a）浓度与溶解无机氮（DIN）浓度、溶解无机磷（DIP）浓度、溶解硅（DSi）浓度、水温、浊度和溶解氧浓度等环境因子的分布特征.结果表明：1）水库属于中营养水体，表层主要浮游藻类（细胞丰度>1000 cells/L）有34种，平均生物量为0.41 mg/L.主要优势藻类（优势度≥0.02）为硅藻和蓝藻，藻类组成与DIN浓度、DIP浓度、DSi浓度和水温等环境因子关系密切，4种因子对藻类结构的解释水平达60%以上.2）水库水体Chl.a浓度具有显著的次表层叶绿素最大值（SCM）现象，SCM层深度为3~8 m，厚度为2~7 m，SCM层占整个水体的25.2%~74.1%.SCM层的藻类对营养盐吸收消耗致使DIN、DIP和DSi浓度下降，同时藻类的产氧使溶解氧浓度增加.3）水库对DSi具有显著的生物过滤器效应，中、上层约有11%~12%的DSi被生物吸收利用，从上游至下游，累积约有21%的DSi被藻类吸收沉降于库底.4）人类氮、磷排放对水库生态和水质有严重影响，毗邻县城区域水体的Chl.a和DIP浓度分别是自然河段的2.9倍和3倍左右.;Zhelin Reservoir is a large canyon-reservoir in the midstream of the Yangtze River, and the storage capacity is 79.2×10⁸ m³ and length is 115 km. Through measurements on a moving vessel and at fixed-point sites in the Zhelin Reservoir in April, 2015, the distribution of phytoplankton, chlorophyll-a (Chl.a) concentration and main environment variables (including dissolved inorganic nitrogen (DIN), dissolved inorganic phosphorus (DIP), dissolved silicon (DSi), water temperature, turbidity, dissolved oxygen (DO)) were analyzed. The redundancy relationship of phytoplankton taxa and environmental variables was analyzed using the software CANOCO 4.5. The results showed that, 1) the reservoir water was categorized as a middle-status in nutrients. There were 34 main phytoplankton species in the surface (the cell density of which exceeding 1000 cells/L), and the average biomass of reservoir was 0.41 mg/L. The dominant algae (dominance be equal or greater than 0.02) were the diatoms and cyanobacteria. DIN, DIP, DSi and water temperature can impact on the structure of algae, and the four factors were explained for more than 60% variation of the algal structure. 2) The reservoir had a significant phenomenon of subsurface chlorophyll maximum (SCM). The depth of SCM appears at the water depth from 3 to 8 m, and the thickness is about 2-7 m. The Chl.a in the SCM layer is 25.2%-74.1% among the total in the vertical. The algae in the SCM layer absorbed the nutrients, resulting in decreased concentrations of DIN, DIP and DSi and the increased DO concentration. 3) The reservoir had significant biological and biochemical filtering effect for the DSi. About 11% to 12% DSi were absorbed by organisms in the middle and upper area of in the reservoir, and accumulating about 21% DSi was absorbed by algae from upstream to downstream. 4) Nitrogen and phosphorus emissions by human activities have a serious impact on the ecology and water quality of the reservoir and the adjacent county region. The concentrations of Chl.a and DIP in the region is about 2.9 times and 3 times higher than that in the natural region of the reservoir, respectively.