MEASUREMENTS OF METHANE FLUXES ON THE LANDSCAPE SCALE FROM A WETLAND AREA IN NORTH SCOTLAND

Atmospheric profiles of methane have been measured using an aircraft over an area of natural wetland in Northern Britain, Caithness and Sutherland, in Scotland. The measurements showed a clear horizontal gradient in methane concentration as air was advected over the wetland area from the Atlantic Ocean and a strong decrease in concentration in the vertical. The data, together with those from ground-based measurements including continuous measurements at an instrumented field site, were used to estimate area averaged fluxes using a simple diffusion model. The mean flux for the region was calculated to be 0.91 +/- 0.51 mug m-2 s-1. Methane source strengths for the NW region of Scotland were a factor of 2-3 times larger than for the NE region. Nocturnal methane fluxes were estimated at the field site from temporal concentration changes in methane near the surface and doppler sodar measurements of the boundary layer depth. Night time fluxes were found to be 0.45 +/- 0.28 mug m-2 s-1 and were comparable to those measured using the flux gradient technique at the same site. The aircraft area averaged fluxes were typically a factor of 2-4 times larger than those measured by cuvette techniques at the surface. This was probably due to the dryness of the site relative to the area to the west.