Poster Presentation Freshwater Sciences 2023

The role of redox: nutrient availability in porewater across varying soil saturation conditions in the arctic tundra (#612)

Erin VanderJeugdt 1 , Erin Rooney 2 , Lauren Kinsman-Costello 1 , Elizabeth Herndon 2 , Michael Weintraub 3 , Imitaz Miah 3 , Kristen Bidas 2
  1. Kent State University, Kent, OHIO, United States
  2. University of Tennessee Knoxville, Knoxville, Tennessee, United States
  3. University of Toledo, Toledo, Ohio, United States

The arctic tundra contains perennially frozen ground that thaws every growing season, termed the active layer. As the active layer thaws, topography and soil type control varying levels of saturation and therefore oxygen availability. In fully saturated soils, dissolved oxygen concentrations may become anoxic, causing microbial metabolism to perform anaerobic respiration. As the frozen ground thaws throughout the growing season, the water table shifts: water-logged soils that were frozen early in the growing season can drain, allowing oxygen to permeate soil pores and energetically favorable aerobic respiration to occur. With warming temperatures in the arctic, permafrost at greater depths may thaw, changing the depth of the water table and groundwater drainage across the landscape. Monitoring redox (reduction-oxidation) conditions in the soil profile allows us to indicate which forms of anaerobic respiration are energetically favorable. By pairing redox conditions with porewater nutrient concentrations (nitrate, ammonium, and phosphate), we can conclude whether these nutrients are the result of anaerobic respiration. Our two main research questions are: 1) How does redox potential change as the thaw depth increases through the growing season?  2) Do these changes affect nutrient availability, mainly concentrations of nitrate, ammonium, and phosphate? We established three study sites along a hillslope with varying saturation conditions near Toolik Field Station, AK. We installed three redox probes at each study site at the beginning of the growing season; readings were taken along the soil profile from 0-50cm in 15-minute intervals. We collected porewater samples weekly near each of the redox probes at 10cm, 20cm, and 40cm depths for concentrations of nutrients and iron. Oxic conditions in our well-drained and mid-saturation soils up to 30cm, while the fully saturated soils show increasingly anoxic conditions through the season and with depth; these trends could explain the measured ammonium and phosphate concentrations across sites.