ABSTRACT

The responses of phytoplankton to the spatial variation of 2 tropical reservoirs with long water-residence times was studied by means of morphology-based functional groups (MBFGs). The groups were compared among the pelagic, tributary, and downstream zones to determine the spatial distribution and its main drivers. Based on the zonation concept, we hypothesized that phytoplankton tolerant to nutrient depletion would be more important in the pelagic zones, and phytoplankton resistant to light limitation and turbulence would be more important in the lotic zones. We also expected nutrients and/or light availability (bottom-up control) to be the main drivers of MBFGs spatiality in tropical systems. Our results indicated the importance of this control for phytoplankton spatial distribution. The phytoplankton biovolume was more homogeneous in Serra da Mesa Reservoir (SER), while in Três Marias Reservoir (TRM) biovolume was higher in the pelagic zone. MBFG III dominated in the pelagic zone of TRM while MBFG V dominated in its tributary. The higher biovolume of MBFG III was associated with low dissolved phosphate and high water temperature and pH in SER, and lower dissolved inorganic nitrogen and high pH in the pelagic zone of TRM, as shown by RDA analyses. The dominance of MBFG V in the tributary is probably a response to higher turbidity and dissolved organic carbon availability. We conclude that within zones, resources (nutrients and light availability), temperature, and pH were the main drivers of the phytoplankton in these reservoirs. Furthermore, the MBFG scheme can be used to monitor phytoplankton spatial distribution.

抽象的

利用基于形态学的功能群（MBFGs）研究了浮游植物对2个长水生时间热带水库空间变化的响应。在浮游，支流和下游区域之间对这些组进行了比较，以确定空间分布及其主要驱动力。基于分区的概念，我们假设对营养耗尽的浮游植物在中上层地区更为重要，而对光限制和湍流有抵抗力的浮游植物在上层地区更为重要。我们还期望营养物和/或光的可用性（自下而上控制）将成为热带系统中MBFG空间分布的主要驱动力。我们的结果表明了这种控制对浮游植物空间分布的重要性。塞拉达梅萨水库（SER）的浮游植物生物量更为均匀，而特雷斯玛丽亚斯水库（TRM）的浮游生物量在中上层地区较高。MBFG III在TRM的上层带中占主导地位，而MBFG V在其支流中占主导地位。如RDA分析所示，MBFG III的较高生物量与SER中的低溶解磷酸盐，高水温和pH值有关，而与TRM中上层带较低的溶解无机氮和高pH有关。支流中MBFG V的优势可能是对更高的浊度和溶解的有机碳可利用性的反应。我们得出结论，在这些区域内，资源（营养物和光的利用率），温度和pH值是这些水库中浮游植物的主要驱动因素。此外，MBFG方案可用于监测浮游植物的空间分布。