Date of Graduation
Honors Research Project
Bachelor of Science
Dr. Anne Wiley
Dr. Randy Mitchell
Dr. Shanon Donnelly
Wetlands are important in filtering pollutants from aquatic ecosystems and also serve as habitats for a diverse array of organisms. However, wetland-river networks are often subject to human disturbances such as dyke construction. These decreases in connectivity have the potential to impede movement of organisms and nutrients between habitats.
This study examined how the food web structure and diversity of macroinvertebrate communities differ between wetland sites connected and disconnected to nearby rivers. According to macroinvertebrate surveys in wetlands connected to nearby rivers and dyked wetlands (not connected to nearby rivers), there is an increase in average species richness and diversity (Shannon index) in connected sites. This may be because wetland-river connections provide opportunities for species to enter adjacent ecosystems. I used stable isotope analyses to examine the impact of species diversity and connectivity on the nutrient source and trophic position of odonates (dragonflies and damselflies)- top predators in many wetlands. Because stable nitrogen isotope values (δ15N) increase by 3-5 ‰ with each trophic transfer, the offset in δ15N between odonates and amphipods (primary consumers in wetland food webs) served as a proxy for food chain length. Although there was not evidence to conclude that the offset in δ15 N is greater in connected wetlands, average Odonate δ15N values in sites connected to a river were higher than in dyked sites. This observed shift in δ15N may be an indication of different nitrogen inputs to connected and disconnected wetlands, specifically, the relative input of terrestrial (allochthonous) nutrients. Notably, amphipods are often assumed to be primary consumers in wetlands. However, amphipods in this study had variable δ15N values, providing evidence for the claim that they can function as both primary consumers and secondary-tertiary consumers.
While managers increasingly promote the restoration of natural connectivity between wetlands and rivers, there are few studies showing the likely impacts to wetland food web structure. My research will help to fill this gap and provide a more solid foundation for management decisions aimed at preserving wetland biodiversity.
Hodgson, Samantha M.; Pollock, Jacob; and Wiley, Dr. Anne E., "Wetland Connectivity and Macroinvertebrate Diversity" (2017). Williams Honors College, Honors Research Projects. 527.