Effects of land use on greenhouse gas fluxes and soil properties of wetland catchments in the Prairie Pothole Region of North America

Abstract:

Wetland restoration has been suggested as policy goal with multiple environmental benefits including enhancement of atmospheric carbon sequestration. However, there are concerns that increased CH₄ emissions associated with restoration may outweigh the potential sequestration benefits. The Prairie Pothole Region (PPR) of North America is characterized by millions of depressional wetlands and spans climate and land-use gradients that have potential to affect biotic and abiotic factors associated with the overall greenhouse gas (GHG) balance of pothole wetland ecosystems. Thus, we conducted a comprehensive, 4-year study of 119 wetland catchments distributed throughout the U.S. portion of the PPR to assess the effects of land use and restoration practices on CH₄ and N₂O fluxes and soil properties.

Results showed that the effects of land use on GHG fluxes and abiotic soil properties differed with respect to catchment zone (upland, wetland), wetland classification, geographic location, and year. CH₄ fluxes were greater than previously reported for pothole wetlands, while N₂O fluxes were comparable to previously reported values. Moreover, maximum cumulative CH₄ fluxes were nearly 3 times as high as previously reported in North America.

Results suggest that soil organic carbon is lost when relatively undisturbed catchments are converted for agriculture, but sequestration rates associated with restoration are variable. Further, when non-drained cropland catchments are restored, CH₄ fluxes generally are not different than the pre-restoration baseline; conversely, when drained cropland catchments are restored, CH₄ fluxes are noticeably higher. Consequently, it is important to consider the type of restoration when assessing restoration benefits. Results also suggest that elevated N₂O fluxes from cropland catchments likely would be reduced through restoration. The overall variability discovered by this study underscores the difficulty in quantifying the GHG balance of wetlands.