Oral Presentation Freshwater Sciences 2023

Spatial and temporal variation in quantity and bioavailability of dissolved organic carbon within a metropolitan area (#436)

Annika M Quick 1 , Allison H Roy 2 , Rebecca L Hale 3 , Krista A Capps 4 , Kristina G Hopkins 5 , John S Kominoski 6 , Jennifer L Morse 7 , Shuo Chen 8 , Christopher Rizzie 6 , Liz Ortiz Munoz 6
  1. Virginia Wesleyan Unviersity, Virginia Beach, VA, United States
  2. U.S. Geological Survey, Massachusetts Cooperative Fish and Wildlife Research Unit, University of Massachusetts Amherst, Amherst, MA, USA
  3. Smithsonian Environmental Research Center, Edgewater, MD, USA
  4. Odum School of Ecology & Savannah River Ecology Laboratory, University of Georgia, Athens, GA, USA
  5. U.S. Geological Survey South Atlantic Water Science Center, Raleigh, NC, USA
  6. Institute of Environment & Department of Biological Sciences, Florida International University, Miami, FL, USA
  7. Department of Environmental Science and Management, Portland State University, Portland, OR, USA
  8. Odum School of Ecology, University of Georgia, Athens, GA, USA

The magnitude, bioavailability, and timing of fluxes of dissolved organic carbon (DOC) in riverine systems are key factors in stream ecosystem functions, including nutrient cycling. Urban riverine systems are complicated by variability in impervious cover, wastewater and stormwater infrastructure, riparian cover, and channelization, which affect autochthonous and allochthonous sources and transport of carbon. We sampled stream water from 100 sites in the greater Boston (Massachusetts, USA) area reflecting a broad gradient of watershed land cover, riparian vegetation, stream size, housing and infrastructure age, and socio-demographic characteristics. Water samples collected from tributary and mainstem sites in the Mystic, Charles, and Neponset River watersheds during four synoptic events—late summer of a wet year (September 2021), during leaf fall (November 2021), during spring leaf out (April 2022), and mid-summer of a dry year (July 2022)—were analyzed for the concentration, absorbance, and fluorescence of DOC. Seasonally, DOC concentrations were highest in April and July. DOC characteristics shifted from more allochthonous and humic in the fall and spring to more autochthonous, lower-molecular-weight DOC in July. Spatially, we observed lower DOC concentrations in September and November in streams draining areas with high population density, impervious cover, and environmental justice communities, although this trend is reversed in April and July. More of the DOC in highly developed areas was from autochthonous sources, suggesting that nutrient inputs and open canopies increase autochthonous carbon production, which is more bioavailable for stream metabolism than allochthonous sources. Increasing carbon bioavailability with urbanization has implications for stream ecosystem function and water quality, including increased rates of in-stream respiration, oxygen depletion, nutrient cycling, and lower residence times. Both the impacts of urbanization on riverine DOC quantity and quality and potential impacts of changes in DOC on water quality merit further study.