The Impact of Hydrologic Connectivity on Macroinvertebrate Biodiversity in the Shiawassee National Wildlife Refuge

Abstract

Recovering obstructed hydrologic connectivity can be an important goal of restoration work in wetland ecosystems. Diked floodplain units, even when intensively managed, are often variably disconnected from adjacent river systems and thus present an interesting opportunity for studying the impacts of variations in hydrologic connectivity on floodplain communities. Both diked and naturally connected floodplains exist in the Shiawassee National Wildlife Refuge. The goal of my study was to assess how diked unit location and configuration influence the structure of macroinvertebrate community richness. Using nested samples from vegetated microhabitats within larger floodplain units, aquatic macroinvertebrate surveys were conducted in the spring and summer of 2016. Water quality measurements were collected in the field while hydrologic connectivity was determined from existing map and LIDAR data layers. Trophic diversity was also studied through stable isotope analysis of top predators, common odonates, in the systems. Results suggest dike height (a proxy for flooding frequency) and channel distance from the river were important in determining community structure and richness within the refuge. Significant reductions in the taxonomic richness of floodplain macroinvertebrate communities were seen with increasing height and channel distance; in the refuge, each additional 1-meter in dike height reduced floodplain richness on average by one genus. Flooding height also significantly reduced the crustacean and gastropod diversity, altering the food web as seen in the significantly variable carbon and nitrogen isotope values. Stable isotope data showed higher trophic diversity in strongly connected sites, supporting my findings with respect to community composition. These results will be beneficial in assessing the impacts of the refuge’s recent and future hydrologic restoration projects, and in general, my findings support the refuge’s goals of monitoring improvements in wetland function and diversity.