Monday, November 13, 2006

Surface Emissions and Soil Profile Concentrations of Greenhouse Gases in a Prairie Pot-hole Landscape.

Nandakumar Rajendran1, Mario Tenuta1, and David L. Burton2. (1) Dept. of Soil Science, University of Manitoba, Winnipeg, MB R3T2N2, Canada, (2) Dept. of Engineering, Nova Scotia Agricultural College, Truro, NS B2N 5E3, Canada

The concentration of greenhouse gases (GHGs) namely carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) are increasing in atmosphere and believed to cause warming of the earth. Agricultural soils account for considerable portion of GHG emissions from anthropogenic sources. Landscape of Prairie Pot-hole region of Latin North America is undulating and to what extent landscape positions influence GHG emissions is unknown. We suspected water to be a major driver of GHG emission in the landscape, particularly altering production, consumption and transport of GHG to the surface. A field experiment was conducted north of Brandon, Manitoba with Upper, Middle, Lower and Riparian landscape positions examined. Soil atmosphere and surface flux gases were collected August 2005 to November 2005 and March 2006 to August 2006 using silicone gas probes and static-vented chambers. Volumetric moisture content (VMC) and oxygen concentrations of profiles were also determined. VMC for all slope positions increased with depth and was highest for Lower and Riparian positions. GHG concentrations did not vary with depth at Upper and Middle positions whereas they increased with depth at Lower and Riparian positions. Prevalence of anaerobic condition was evident by low oxygen concentration and highest VMC in Lower and Riparian positions, associated with highest N2O and CH4 concentration. However, N2O surface emissions were not substantial in these positions indicating N2O accumulated at depth was reduced in overlying soil. Increasing CH4 concentration with depth for the Riparian position was associated with high CH4 surface flux. Like N2O, CH4 produced at depth in Lower position did not lead to appreciable surface emissions. Our results demonstrate water content particularly determines the pattern of GHG emitted from lower positions in Prairie Pot-hole landscapes. In dry years N2O and CH4 are reduced and oxidized in overlying soils respectively and in wet years they are released to atmosphere.

Handout (.pdf format, 4284.0 kb)