Linking Soil Profile Greenhouse Gas Concentrations to Surface Emissions in a Prairie Pothole Agricultural Landscape.

Agricultural landscapes of the Prairie Pothole Region (PPR) of North America feature complex topography and hydrology, posing a significant challenge for estimating emissions of greenhouse gases (GHG) to the atmosphere. This study examined the linkage of soil profile concentrations of GHG (N₂O, CH₄ and CO₂) and O₂ in relation to GHG surface emissions from a PPR agricultural field near Brandon, Manitoba. The field was segmented into the four landscape elements including cropped Upper, Middle, Lower and uncropped Riparian. Soil profile gas concentrations at 5, 15, 35 and 65 cm depths and surface emissions were measured through fall 2005 and the 2006 growing season of flax. Soil gas contents to 65 cm were also estimated. Spring thaw caused a substantial increase in concentrations and contents of N₂O at 15-35 cm at the Lower and Riparian elements, though surface emissions increased only at the former. This suggests N₂O accumulated during spring-thaw but consumed under prolonged anaerobic conditions of the Riparian element. Application of N fertilizer increased soil contents and emissions of N₂O from all cropped elements. Compared to spring-thaw, addition of N fertilizer resulted in less N₂O accumulation but even higher surface emissions from the Lower element. A deeper profile accumulation during spring-thaw than following fertilizer addition suggests a greater distance for vertical transport could have increased consumption and thus reduced emissions of N₂O.  The Riparian element had consistently the highest CH₄ emissions, which occurred after spring-thaw N₂O emissions with increased soil CH₄ and decreased O₂ concentrations. Soil concentrations and contents of CO₂, as well as surface emissions, followed the trend of soil temperature, with values consistently higher at the Riparian than cropped elements. The study clearly suggest the variability in GHG emissions between landscape positions are associated with their accumulations in soils and soil environmental conditions, especially the moisture and aeration conditions.