Stream ecosystems are increasingly under pressure from urban land development and altered hydrological regimes. Microorganisms play vital roles in stream nutrient cycling, transforming and taking up dissolved carbon and nitrogen while also generating biomass for the basal food web. With the expansion of urban centers and the increased drying of perennial streams, understanding how these factors affect microbial communities will help us understand integrated stream ecosystem health and metabolism. This study investigates how land use and flow permanence (perennial vs. non-perennial) shape microbial community composition and function, measured using prokaryotic and protistan gene sequencing and decomposition extracellular enzyme activity (EEA) potentials, respectively. We predicted that community composition would differ between flow regimes and that urban land use would exacerbate that dissimilarity, and that urban land use would suppress EEA due to potential increases in nutrient concentrations. We collected benthic sediment, epilithic biofilm, leaf litter, and water column samples from headwater tributaries (n=24) to East Fork Poplar Creek in Oak Ridge, TN, at locations including perennial and non-perennial headwaters along an urban-to-forested gradient. Bacterial community composition was determined by 16S rRNA gene metabarcoding and high-throughput sequencing, and EEAs were measured using fluorescence assays.
Preliminary analysis reveals that both sediment (p = 0.002) and epilithic biofilm (p = 0.04) community compositions are influenced by the percentage of urban land development. Further, sediment communities were dissimilar between flow regimes (p = 0.01), whereas epilithic communities were not. Functional patterns were weaker, as EEAs in epilithon did not vary across the study gradients, and benthic sediment nitrogen-acquiring enzymatic activity negatively correlated with urban development (p = 0.08, rho = -0.24) but did not vary with flow permanence. Additional results from the water column and leaf litter communities are forthcoming, as is protistan community composition, and comparisons between summer, fall, and winter seasons. Our initial findings suggest that the microbial community response differs across microhabitats, with the sediment community more sensitive to land-use and flow-regime factors. Understanding how microorganisms across stream microhabitats are affected by anthropogenic changes will give us a more comprehensive picture of the health and metabolism of our stream ecosystems.