CLIMATE WARMING CONSTRAINS GREENHOUSE GAS EMISSIONS OF AGRICULTURAL RESERVOIRS IN THE NORTHERN GREAT PLAINS

Inland waters are well known to be biogeochemical hotspots for carbon cycling, and have accordingly have been well studied in terms of quantifying rates and underlying controls of greenhouse gas emissions. The complex interplay of multiple mechanistic factors, however, can make scaling emissions rates at the landscape scale difficult, particularly for understudied hard-water ecosystems. Based on extensive research on small agricultural reservoirs in the northern Great Plains between 2017-2023, we found simple correlative relationships whereby CO₂ emissions were well predicted by water-column pH, and both diffusive and ebullitive CH₄ emissions were correlated with salinity. Specifically, CH₄ ebullition rates were effectively zero above a water-column salinity of 0.5 ppt, and diffusive losses were constant and low (mean 3.2 + 9.5 mmol/m²/day) above that threshold, consistent with prior surveys of 100s of similar ecosystems. Importantly, ebullition rates could be predicted from water-column CH₄ content (R² = 0.56, P< 0.05).  Given that the median salinity of water bodies in this region is 0.41ppt, drought conditions may constrain methane emissions and shift small water bodies from net carbon sources to sinks during dry intervals. Similarly, warmer winters are anticipated to elevate water column pH and reduce CO₂ emissions. The ability to forecast greenhouse gas responses to climate variability is essential to accurately quantify the role of small reservoirs in the National Inventory Report, particularly in light of the expected 3-5^oC increase in regional temperature.

Primary Presenter: Kerri Finlay, University of Regina (kerri.finlay@uregina.ca)

Authors:

Kerri Finlay, University of Regina  (kerri.finlay@uregina.ca)

Ryan Rimas, University of Regina  (ryanivanrimas@gmail.com)

Sydney Jensen, University of Regina  (sydney.jensen@uregina.ca)

Michael Mensah, University of Regina  (mikemenz253@gmail.com)

Jackie Webb, Deakin University  (j.webb@deakin.edu.au)

Jesse Chadwick, University of Regina  (jac443@uregina.ca)

Heather Sauer, Saskatchewan Water Security Agency  (heather.sauer@wsask.ca)

Cynthia Soued, University of Lethbridge  (cynthia.soued@gmail.com)

Matthew Bogard, University of Lethbridge  (matthew.bogard@uleth.ca)

Peter Leavitt, University of Regina  (peter.leavitt@uregina.ca)