Structural changes of the phytoplankton and epiphyton in an urban hypereutrophic reservoir

Abstract: Aim This study evaluated the temporal changes of phytoplankton and epiphyton structure and their relationships with limnological factors in an urban hypereutrophic reservoir (Rasgão Reservoir, Brazil). Methods We collected water sample and phytoplankton in different depths at two sites (dam and near tributary input) in summer and winter 2010. Epiphyton on Salvinia spp. was sampled only at site near the tributary input. We determined limnological variables and structural attributes (species composition, density, biovolume, descriptors species, diversity) for both communities. Results Phytoplankton density and epiphyton density and biovolume were higher in the winter (dry season), which occurred the higher nutrient concentrations and lower water flow. Chlorophyceae was dominant in the phytoplankton in both period and Cyanobacteria was the second most abundant class in the winter. In the epiphyton, Bacillariophyceae was dominant in the summer and Cyanobacteria in the winter. The increase in light availability and water flow can have provided high species richness and diversity in the summer. Conclusion Temporal changes in the structure of phytoplankton and epiphyton on Salvinia were more related to increased nutrients availability (nitrogen and phosphorus) and flow variations in a hypereutrophic reservoir.

摘要：本研究旨在评估巴西拉斯冈水库（Rasgão Reservoir）这一城市超富营养化水库中，浮游植物（phytoplankton）与附生藻类（epiphyton）的群落结构时间演变特征，及其与湖沼学因子（limnological factors）的关联。
研究方法：2010年夏、冬两季，研究人员于大坝及支流入水口附近两个采样点的不同深度采集水样与浮游植物样本；仅在支流入水口附近的采样点采集槐叶萍属（Salvinia spp.）表面的附生藻类样本。针对两类群落，测定了其湖沼学变量及结构属性，包括物种组成、密度、生物体积（biovolume）、指示物种及多样性指标。
研究结果：冬季（旱季）的浮游植物密度、附生藻类密度与生物体积均高于夏季，该时期水库营养盐浓度更高且水流流速更低。两个采样季的浮游植物均以绿藻门（Chlorophyceae）为优势类群，冬季蓝藻门（Cyanobacteria）为第二优势类群。附生藻类群落则在夏季以硅藻门（Bacillariophyceae）为优势类群，冬季则以蓝藻门为优势类群。夏季更高的光照可获得性与水流流速可能促成了更高的物种丰富度与多样性。
研究结论：在该超富营养化水库中，槐叶萍表面浮游植物与附生藻类的群落结构时间变化，主要与氮、磷营养盐可利用性提升及水流流速变化密切相关。