Phytoplankton functional groups evidence environmental differences in a temperate floodplain.

Abstract

Floodplain environments have high biodiversity and provide many ecosystem services maintained by the flood pulses. The phytoplankton is essential to the functioning of these ecosystems, acting upon primary productivity and biogeochemical cycles. We evaluated phytoplankton in a river-lake flood system (Illinois River floodplain-USA) during a hydrological cycle and compared the taxonomic (species) and functional (morphologic-based functional groups – MBFG) approaches. As expected, greater species richness was registered in the river and higher biovolume in the lake, as well as the predominance of different MBFGs in each environment. Furthermore, seasonality drove richness and biovolume temporal variation due to the higher water levels during spring. The MBFG IV (i. e. without specialized traits), V (phytoflagellates) and VI (diatoms) were more important for richness and biovolume in both environments. We reinforce the fundamental role of the hydrodynamics characteristics, with higher phytoplankton biovolume values in the lake. Using MBFG resulted in a better explanation to the phytoplankton-environment relationship. Constant water column mixture and high turbidity selected species with traits (e.g. small size, presence of silica) specifically adapted to these conditions.