Lateral variations of aquatic invertebrate community structure along the floodplains of the Altamaha and Savannah Rivers in Georgia, USA

Many large rivers are regulated by dams and levees, and the connectivity of the river to the adjacent floodplain is being reduced.  We assessed floodplain invertebrate community structure and biomass in seasonal backwater swamps of the Savannah and Altamaha Rivers in Georgia, USA with three differing connectivity regimes: 1) near the river’s edge, 2) in the floodplain interior, removed from both the river and upland, and 3) near the upland edge.  Flows in the Savannah River are regulated, while flows in the Altamaha River are natural. We predicted that the invertebrate community structure closer to the river will be dominated by organisms from the river, while habitats adjacent to the upland will be dominated by terrestrial organisms.  Habitats in the floodplain interior should support more “true wetland” organisms.  In 2007 and 2008, we used a Hess sampler to collect invertebrates in the water column and on benthic substrates, and sampled in late winter (February-March) soon after wetlands seasonally flooded, and again in spring (April). Preliminary analyses suggest that communities differ significantly among sites near the river, in the floodplain interior, and near the upland in ways that at least partially support our hypotheses.