Temporal Patterns of Aquatic Macroinvertebrate Communities and Organic Matter Standing Stock Availability in a Coastal Floodplain (Altamaha River, Georgia)

River floodplain habitats of the Southeastern United States are sites of high biological productivity that rely on a predictable flooding event as a keystone process. This study took place in a river-floodplain area of the Altamaha River, an unimpounded large-order river in the Coastal Plains region of the US. This study aims to investigate how aquatic macroinvertebrate communities changed over the course of the annual flood pulse. I predicted that the communities would be different and that the differences would be driven by hydrology at the main stem and organic matter standing stock availability. I took quantitative samples of benthic macroinvertebrates monthly from December 2011-April 2012 and from December 2012- April 2014. Invertebrate abundance was assessed and biomass was obtained using published length-mass regressions. Year 1 (2011-2012) was characterized by severe drought. And Year 2 was characterized by a large flooding event. There was a significant difference between the communities. In year 1 the community was influenced by hydrology and high FBOM standing stocks. In year 2 the community was influenced by hydrology and low CBOM standing stocks. This study shows the importance of a flooding event in river floodplain systems and supports the idea that floodplains act as a source of organic matter to the main stem and are sites of high biological productivity especially from aquatic macroinvertebrates. As unimpounded rivers are becoming increasingly rare, it is important to understand how these systems function in both normal and abnormal (i.e., drought vs. flood) conditions