Controls of Carbon Dioxide, Methane, and Nitrous Oxide Emissions in
Natural and Constructed Agricultural Waterbodies on the Northern Great
Plains
Abstract
Inland waters are hotspots of greenhouse gas (GHG) emissions, and small
water bodies are now well known to be particularly active in the
production and consumption of carbon dioxide (CO2),
methane (CH4), and nitrous oxide (N2O).
High variability in physical, chemical, and environmental parameters
affect the production of these GHG, but currently the mechanistic
underpinnings are unclear, leading to high uncertainty in scaling up
these fluxes. Here, we compare the relative magnitudes and controls of
emissions of all three major GHG in twenty pairs of natural wetland
ponds and constructed reservoirs in Canada’s largest agricultural
region. While gaseous fluxes of CO2 and
CH4 were comparable between the two waterbody types,
CH4 ebullition was greater in wetland ponds. Carbon
dioxide levels were associated primarily with metabolic indicators in
both water body types, with primary productivity paramount in
agricultural reservoirs, and heterotrophic metabolism a stronger
correlate in wetland ponds. Methane emissions were positively driven by
eutrophication in the reservoirs, while competitive inhibition by
sulfur-reducing bacteria may have limited CH4 in both
waterbody types. Contrary to expectations, N2O was
undersaturated in both water body types, with wetlands a significantly
stronger and more widespread N2O sink than were
reservoirs. These results support the need for natural and constructed
water bodies for regional GHG budgets and identification of GHG
processing hotspots.