Decreasing Richness and Biomass During a Flood Pulse Observed in a Southeastern US Coastal Floodplain Following a Multi-Year, Supra-Seasonal Drought

Floodplains of the southeastern United States exhibit high biological abundance and diversity, maintained by periodic inundation from seasonal flooding. To examine the relationship between invertebrate community composition and seasonal flooding following periods of drought, we quantified aquatic macroinvertebrate communities monthly in an inundated floodplain during the annual flood pulse (December-April) in two years: one following a multi-year drought and one during a larger than average flood. We predicted that floodplain communities would differ in richness, biomass, and community composition between years and that differences would be driven by the annual flood pulse and organic matter availability. We collected macroinvertebrates from a floodplain of the Altamaha River, a free-flowing 6th order river in the Coastal Plain region of the southeastern US. With invertebrates identified to genus, we estimated richness, abundance, biomass, community composition, and proportions of functional feeding group abundance. Richness was generally higher in the drought year but decreased throughout the flood pulse, while during the flood year richness was lower and increased over time. Biomass decreased throughout the flood pulse following the drought year and increased during the flood year. There was high overlap in invertebrate community composition based on abundance data during both years of the study with collector gatherers being the most abundant functional feeding group. Our study provides insight to the response of aquatic communities to an extended drought and subsequent return to normal flow in a lower river wetland.