CHARACTERIZATION OF WATER QUALITY AND PERIPHYTON ASSEMBLAGES IN AN URBAN STREAM, KNOXVILLE, TENNESSEE

Periphyton consists of assemblages of algae, diatoms, organic matter, and other microorganisms that grow on rock, sediment, and plant surfaces in aquatic systems. Periphyton growth and diversity can be affected by a range of environmental factors, but there have been few studies to understand periphyton diversity in nutrient-impaired waterways, such as in Tennessee. This study investigated whether stream periphyton communities could be used to indicate different levels of potential impairment. The study took place along a 4.8-kilometer-long segment of Third Creek in Knoxville, Tennessee. Twelve sites were selected and samples were collected at base-flow conditions in July, September, and October 2021, and in January 2022. Physical stream assessments indicated that bank stability and bank erosion conditions were poor, and 10 of 12 sites had at least one anthropogenic input (e.g., drainpipe) into the stream. More than half of the sites had land use / land cover (LULC) classified as 50% or more developed (i.e. urban). Although some water quality parameters did not indicate impairment, such as oxygen concentrations or chlorophyll a concentrations, others parameters did, including total nitrogen, which exceeded minimum recommended levels at all sites, and E. coli counts at almost all locations that exceeded recommended thresholds for recreational streams. The 16S rRNA and 18S rRNA gene sequence diversity of water and periphyton samples revealed differences in dominant taxonomic groups along the stream. Among the Bacteria, the phyla Proteobacteria, Actinobacteria, Bacteroidota, Firmicutes, Campilobacterota, Nitrospira, Verrucomicrobiota, Planctomycetota, and Myxococcota had high relative abundances in the water, and eukaryotic phyla Cilophora, Diatomea, and Cryptophycae were abundant. Periphyton communities were dominated by Proteobacteria, Cyanobacteria, Planctomycetota, Chloroflexi, Actinobacteriota, Acidobacteriota, and Bacteroidota, with prevalent eukaryotic phyla being Florideophycidae, Diatomea, Phragmoplastophyta, Chlorophyta, Arthropoda, Rotifera, Nematozoa, and Ascomycota. Bioconcentration factors of trace metals from periphyton biomass revealed that periphyton was significantly enriched in As, Cd, Pb, and Zn compared to concentrations in the water. These periphyton-associated metals could be a source of contamination into the stream and aquatic fauna.