Helena Loucas Senior Thesis Spring 2025

Urbanization causes the degradation of streams described as the Urban Stream Syndrome, resulting in increased contamination, altered stream morphology, and reduced taxonomic richness. Macroinvertebrates vary in their tolerance to the impacts of urbanization, therefore the reduction of taxonomic richness increases the abundance of tolerant species and decreases the abundance of intolerant species. Aquatic macroinvertebrates are specialized feeders, falling into five functional feeding groups which affect ecosystem processes such as the decomposition of organic matter. Through a reduction of intolerant taxa, functional feeding diversity will be reduced because the functional feeding groups are not equally distributed across all tolerance levels. This alteration in functional feeding diversity may affect ecosystem processes within the stream. I hypothesized that the degradation of streams from the Urban Stream Syndrome would result in a decrease in macroinvertebrate diversity and the diversity of the functional feeding groups, altering organic matter processing. To evaluate this hypothesis, I quantified the taxonomic and functional diversity of macroinvertebrate assemblages in an urban and non-urban stream. I then developed a model for organic matter processing using macroinvertebrate consumption rates from the literature and predicted organic matter processing rates in the urban and non-urban stream. I found that there was a reduction in the intolerant macroinvertebrates in the urban stream when compared to the non-urban stream. There was also a reduction in taxonomic and functional diversity in the urban stream. The modeled consumption rates indicated that in the urban stream, Collectors were responsible for the most consumption, whereas in the non-urban stream Shredders were predicted to process the most organic matter. These results support my hypothesis that the Urban Stream Syndrome alters organic matter processing in streams through a shift in macroinvertebrate functional diversity.