Off-channel waterbodies in the Middle Mississippi River: A pilot investigation

Off-channel and floodplain water bodies are important components of large river ecosystems while rare within the Middle Mississippi River. The lack of these habitats likely influences water quality, nutrient processing, and communities of organisms. In early 2016 a major flood event breached two levees south of Cape Girardeau, MO resulting in the creation of two new backwaters—Len Small and Backwater MO 35.5. Water quality, metabolic rate, and fish community data were collected from the new backwaters as well as Horseshow Lake an isolated floodplain lake. Backwater conditions were often different from the main channel with backwaters being warmer and with greater water clarity throughout the study. Nutrient concentrations were often different from the main channel and exhibited similar patterns to those observed in the Upper Mississippi River. One backwater showed high rates of primary productivity (NEP) along with the floodplain lake. Differences between backwater metabolic rates may be due in part to differences in size and connectivity to the river. Fish communities were different between waterbodies with a number of lacustrine species observed in the floodplain lake. Habitat and feeding guilds were also different between waterbodies. Diversity was also not significantly different between waterbodies.

This study represents novel findings for off-channel habitats on the Middle Mississippi River and the opportunity to explore the establishment of new habitat types. Ultimately, we view MO 35.5, Len Small, and Horseshoe Lake as important habitats within the larger riverine ecosystem. There remains much to be learned if restoration activities based on backwater creation within the MMR are to be successful but these preliminary and early stage results indicate these areas are already providing important and variable environmental conditions to riverine organisms.