PPR_UnderIce_JGR2021

Sediment cores were collected under ice-cover in late winter from three wetlands located
along a subsurface hydrologic gradient within the Prairie Pothole Region of North America.
Within each core, sediment porewaters were analyzed by in situ voltammetry for a suite of redox
active species as a function of depth and revealed shifts in complex oxidation-reduction
dynamics related to ice cover in these wetlands. Compared to analogous measurements made
during ice-free conditions in late spring, we observed anoxic to sub-oxic zones much closer to
the sediment-water interface (SWI) that sometimes extended into the overlying water under ice
cover. These findings are consistent with previous observations in shallow Arctic lakes that show
oxygen depletion near the SWI during ice cover, but not under ice-free conditions. Further,
biogeochemical processes varied depending upon wetland type. During winter, sulfide levels in
sediment porewaters in groundwater fed “flow-through” wetlands were significantly
lower than under ice free conditions. The converse applied to groundwater discharge wetlands
where reduced sulfur concentrations in porewaters increased under ice cover. Decreases in ice
cover extent and duration due to climate change coupled with profound landscape changes due to
agriculture will affect the biogeochemical cycles of these wetlands and could lead to increased
carbon emissions in the future.