Influence of re-flooding on phytoplankton assemblages in a temperate wetland following prolonged drought

Wetlands can experience drying and flooding cycles which influence the dynamics of the phytoplankton assemblages. The aim of our study was to evaluate changes in the phytoplankton structure during a drought/flood period in a warm-temperate wetland. We hypothesized that fluctuations in water level and development of macrophytes favour the development of fast-growing algae with adaptations to low light conditions. We studied algal and cyanobacterial colonization and succession in the nascent planktonic habitat in a wetland in the Southern Hemisphere (Argentina). We assessed changes in phytoplankton biovolume, chlorophyll a concentration (Chl a), richness, diversity, and evenness throughout a drought/flood period. Phytoplankton species were classified into ecological functional groups (FG). Multivariate analysis (RDA) showed that water level, conductivity and percentage macrophyte cover of the site surface (PCSS) explained the variability in the phytoplankton assemblage structure in terms of classes and FG. Particularly, FGs T and LM responded to the changes during the drought/flood cycle, probably due to light constraints and stability of the water column induced by the development of emergent and free-floating macrophytes. Our study expands the knowledge of phytoplankton species composition and ecological FG succession under free-floating macrophyte cover in a re-flooding episode. We conclude that water depth and development of macrophytes are the key factors in shaping phytoplankton species structure in a temporary wetland.