Oral Presentation Society for Freshwater Science 2026 Annual Meeting

Dissolved inorganic carbon inputs to streams are shaped by soil respiration, riparian groundwater respiration, and subsurface weathering (134825)

Ashif Hasan Abir 1 , Erin Hotchkiss 2 , Jeremy Jones 3 , David Butman 4 , Kaelin Cawley 5 , Keli Goodman 5 , Frances Iannucci 2 , Kristin Kraus 3 , Hannah Conroy 4 , Wilfred Wollheim 1
  1. Natural Resources and Environment, University of New Hampshire Main Campus, Durham, New Hampshire, United States
  2. Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA, United States
  3. Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, United States
  4. Civil & Environmental Engineering, University of Washington, Seattle, WA, United States
  5. National Ecological Observatory Network, Boulder, CO, United States

Across the terrestrial-aquatic continuum, dissolved inorganic carbon (DIC) and its component species (H2CO3, HCO3-, CO32-) vary across upland soil water, groundwater and surface water. The variation can be attributed to different dominant processes across these pools. Soil respiration produces CO2 in the rooting zone of soil, forming carbonic acid as it dissolves in soil porewater. Once infiltrated into groundwater, this acidic water drives the weathering of carbonate and non-carbonate (e.g., silicate) minerals, releases alkalinity in the form of carbonates and bicarbonates (HCO3-, CO32-), that enters aquatic systems. In undisturbed ecosystems, both respiration and weathering convert biologically produced free CO2 into dissolved alkalinity, acting as a long-term sink for atmospheric CO2. However, the macro-scale controls on observed variation in DIC concentration and speciation across watersheds remain poorly understood.

Using standardized measurements from NEON at 25 co-located terrestrial-aquatic sites, this study asks: (a) How and why do DIC concentration and its component species vary across soil-groundwater-surface water pools over different ecoregions? (b) What  proportion of stream DIC originates from soil respiration vs. subsurface weathering? Results suggest that DIC concentrations are consistently higher in riparian groundwater compared to upland soils across sites (DICgroundwater:DICsoil >1). This difference can be attributed to complex roles of deep subsurface weathering and riparian contribution of respired CO2. DIC concentration decreases from groundwater to streams (DICgroundwater:DICstream >1), indicating evasion of free CO2 from streams into the atmosphere. We further aim to uncover the watershed attributes (e.g., geology, meteorology, channel morphology) that control variation in DIC concentration and speciation across upland soil - groundwater- surface water pools over different ecoregions of the United States.