COS 160-2 - CANCELLED - Analyzing Aquatic Food Webs in Urban Streams through the lens of Ecological Stoichiometry Theory

Abstract: Food webs in aquatic ecosystems are made up of various interactions that can be heavily influenced by the catchment’s dominant land use and land cover (LULC). Urbanization can increase the concentration of dissolved nutrients entering these ecosystems and can therefore affect the nutritional quality of food resources. The presence or absence of canopy cover can also influence aquatic resource quantity and quality. These bottom-up effects of urbanization may influence aquatic macroinvertebrates that consume these resources for growth and reproduction. The quality of their food can help us understand food web structure and function changes in response to urbanization or canopy alteration. Season can also play a role in how much nutrients are entering a stream, due to factors such as the application of fertilizer in the spring and summer, or increased precipitation runoff during the winter. We used ecological stoichiometry theory to examine how urban LULC and the presence or absence of canopy cover across winter and summer affect the elemental content of food resources and macroinvertebrate consumers in stream ecosystems. We expected lower resource and macroinvertebrate carbon:nitrogen (C:N) and carbon:phosphorus (C:P) contents in urban streams with no canopy cover. We sampled fifteen streams in the Central Arkansas metropolitan region: five Forested, five Urban Canopy, and five Urban No Canopy. We collected detrital resources including riparian leaf litter, Coarse Particulate Organic Matter (CPOM), and Fine Particulate Organic Matter (FPOM) as well as periphyton from instream substrates. Macroinvertebrate consumers were also collected and identified to family. All samples were analyzed for elemental contents. Preliminary results indicate that riparian leaf litter C was influenced by LULC (p < 0.01) and plant genus (p < 0.01) with higher leaf litter C in Forested sites than Urban Canopy sites (Tukey HSD, p = 0.02). There was no significant interaction present (p >0.05). Acer sp. and Quercus sp. had higher leaf litter C than Ulmus sp. In contrast, nitrogen content (%N) was not significantly different among LULC and plant genus, and there was not a significant interaction (p >0.05). The molar C:N ratio significantly differed among genera (p = 0.028) but did not significantly differ among LULC and there was not a significant interaction. Acer sp. had higher C:N ratios than Ulmus sp., but did not differ significantly from Quercus sp. Our findings will advance understanding of the flow of elements from food resources to consumers in response to LULC and canopy alteration.