Responses of morphology-based phytoplankton functional groups to spatial variation in two tropical reservoirs with long water-residence time

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.

KEYWORDS:

• bottom-up control
• filamentous cyanobacteria
• phytoflagellates
• spatial dynamic

Acknowledgements

The authors are grateful to ANEEL (National Electrical Energy Agency) and CAPES (Foundation for the Coordination of Higher Education and Graduate Training) for financial support, and to the technical staff of UFJF, especially Mrs Caique Duque Estrada and Gladson Marques for their logistical support in the field and laboratory.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This study was funded by the Centrais Elétricas do Norte do Brasil S/A (ELETRONORTE) and financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES).