Carbon sequestration capacity of a prairie pothole wetland under warm and dry conditions

Abstract

Prairie Pothole wetlands have large temporal changes in water status. The wetlands are often flooded, with water above the soil surface during the early growing season, while becoming dry during the later growing season or for years under strong drought. We used the eddy covariance technique to assess the potential for ecosystem carbon sequestration as a natural climate solution in a large Prairie Pothole wetland in southern Alberta (Frank Lake wetland complex) that was dominated by the emergent macrophyte, Schoenoplectus acutus L. (bulrush). We made ecosystem-scale measurements of CO₂ and CH₄ exchange over two growing seasons during a time-period with environmental conditions that were warmer and drier than the climate normal. In particular, the study was conducted while the wetland had been experiencing a decade-long drought based on the Standardized Precipitation Evapotranspiration Index. To provide perspective on the longer-term temporal variability of ecosystem carbon exchange processes, we also used LandSat NDVI measurements of vegetation greenness, calibrated with eddy covariance measurements of ecosystem CO₂ exchange during 2022–23, to estimate carbon sequestration capacity during 1984–2023, a period that included several wet-dry cycles. Our measured growing season-integrated net CO₂ uptake values were 47 and 70 g C m⁻² season⁻¹ in 2022 and 2023, respectively. Including the measured low methane emissions (converted to CO₂ equivalents based on a Sustained Global Warming Potential) only changed the net sink to 40 and 67 g C m⁻² season⁻¹ in 2022 and 2023, respectively. Despite drought conditions over the last decade, measured ecosystem carbon sequestration values were close to average values during 1984–2023, based on NDVI measurements and model carbon flux calculations. Our results demonstrated net carbon sequestration as a natural climate solution in a Prairie Pothole wetland, even during a time-period that was not expected to be favourable for carbon sequestration because of the drought conditions.