Oral Presentation Freshwater Sciences 2023

Stream CO2 dynamics, sources, and fate in different ecoregions of the United States (#353)

Erin R Hotchkiss 1 , Ashif H Abir 2 , David Butman 3 , Kaelin Cawley 4 , Hannah Conroy 3 , Keli J Goodman 4 , Frances Iannucci 5 , Jay Jones 5 , Kristin Olson 5 , Wilfred M Wollheim 2
  1. Virginia Tech, Blacksburg, VA, USA
  2. University of New Hampshire, Durham, NH, USA
  3. University of Washington, Seattle, WA, USA
  4. National Ecological Observatory Network, Battelle, Boulder, CO, USA
  5. University of Alaska Fairbanks, Fairbanks, AK, USA

Carbon fate and transport within and across ecosystems govern biogeochemical cycles and ecological interactions. Inputs of carbon from soils to streams alter the degree to which terrestrial ecosystems are net carbon sinks and also subsidize respiration and food web energetics in recipient freshwaters. Although the inclusion of streams in regional and global carbon budgets has increased over the last decade, the sources and mechanisms contributing to stream CO2 emissions remain poorly-quantified, especially during high flow events and across different seasons. Furthermore, measurements of in-stream carbon cycling and fluxes can improve our understanding of the carbon forms entering streams (i.e., dissolved or particulate organic matter versus dissolved inorganic carbon). We are integrating high-frequency sensor estimates of stream pCO2 with ongoing monitoring of five stream reaches, their adjacent shallow groundwater wells, and nearby terrestrial plots collocated at National Ecological Observatory Network (NEON) sites to ask: What are the relationships between stream CO2 emissions and export at different timescales? What are the mechanisms and conditions that control stream CO2 fluxes and fate within and across biomes? The sites are characteristic of the United States’ Taiga, Pacific Northwest, southern Rocky Mountains, Appalachian Mountains, and Prairie Peninsula ecoclimatic regions. We will present contrasting relationships between stream discharge and pCO2 within and across ecoregions, with a discussion of mechanisms driving stream CO2 dynamics informed by hillslope well biogeochemistry, estimates of in-stream metabolism, and NEON terrestrial measurements. For example, stream pCO2 at the Rocky Mountain site more than doubled under ice during winter (~500-1500ppm), declined to near-saturation during snowmelt, and gradually increased again during the growing season due to a combination of external CO2 inputs and internal metabolism. We are using these results to develop network-scale models of stream CO2 fluxes and fate that better represent meta-ecosystem carbon fluxes and cycling in different biomes.