Spatial and temporal variation In greenhouse gas flux as affected by mowing on grasslands of hummocky terrain In Saskatchewan

Global climate change has been linked to the increase in greenhouse gas (GHG) emissions. Mixedgrass Prairie of hummocky terrain in Saskatchewan is an understudied landscape contributing an unknown quantity of greenhouse gases (GHGs) to global climate change. The objectives of this study were to determine the effects of topography and mowing on carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) flux and to correlate them with environmental and plant community characteristics. The study site was located in the Northern Mixedgrass Prairie of the Missouri Coteau near Macrorie, SK. April mowing and an unmowed control were imposed on six different landform elements. Carbon dioxide, CH4 and N2O were measured every 7-10 days from spring until fall for two years with closed, vented chambers. Soil physical characteristics, weather and plant community characteristics were measured. Landform element and mowing influenced the flux of all three gases in both sampling seasons. Soil CO2 flux ranged from 3.1 to 23.3 kg CO2-C ha-1 d-1 among the unmowed control plots and 3.6 to 26.4 kg CO2-C ha-1 d-1 after mowing. Soils were a net sink for CH4, consuming 1.4 to 4.4 g CH4-C ha-1 d-1 among the unmowed control plots and 1.8 to 4.1 g CH4-C ha-1 d-1 among the mowed plots. Nitrous oxide flux ranged from -0.25 to 1.17 g N2O-N ha-1 d-1 among the unmowed control plots and -0.20 to 1.51 g N2O-N ha-1 d-1 among the mowed plots. Greenhouse gas flux changed from year-to-year and within years. The greatest GHG flux rate occurred in the depression landform element. Mowing increased the positive flux of CO2 and N2O while increasing the negative flux of CH4. Species composition was correlated with soil water, topography, percentage litter cover and GHG flux rate. Overall, the Mixedgrass Prairie of Saskatchewan likely contributes very little to GHGs. Properly managed, the Mixedgrass Prairie has a well-balanced nutrient cycle that includes various GHGs. The grassland ecosystem plays a role in mitigating climate change by retaining carbon that would be released to the atmosphere with poor grazing management or the conversion to arable agriculture. Government agencies and the ranching industries could best mitigate GHG emissions of Mixedgrass Prairie in Saskatchewan by promoting the retention of above-ground plant material, increasing below-ground carbon sequestration and the avoidance of conversion to cropland