Biogeochemistry and diffuse fluxes of greenhouse gases (methane and carbon dioxide) and dinitrogen from the sediments of oligotrophic Lake Stechlin, northern Germany

Abstract

The total sediment concentrations (both bubble and dissolved phases) of the three major gases, methane (CH 4 ), carbon dioxide (CO 2 ) and dinitrogen (N 2 ), were investigated in the sediments of two basins of oligotrophic Lake Stechlin and their theoretical diffuse fluxes to the sediment-water interface were calculated. CH 4 and CO 2 showed low concentrations in the surface sediments (0.04 and 0.7 mM) increasing with depth (20 cm) to approx. 0.5-0.9 and 0.9-2.0, respectively (higher values were always in the central basin). N 2 showed the opposite distribution, with high surface values (ΔN 2 = 0.8 mM) to averages of 0.25 mM at depth (10-20 cm). Diffuse fluxes to the sediment-water interface from subsurface sediments were calculated as 0.05-0.2 mmole m -2 d -1 (CH 4 ), 2.3-3.4 mmole m -2 d -1 (CO 2 ) and 0.4-5.4 mmole m -2 d -1 (N 2 ) with lower fluxes exhibited in the southern basin (32 m depth) as compared to central basins (68 m) sediments. CO 2 production and diffuse loss in surface sediments represent a major carbon pathway with diffusion calculated to be 20-60 times greater than methane. It is expected that the high concentrations and fluxes for N 2 within the sediment surface showed high rates of denitrification (0.8 mmole m -2 d -1 for southern to 6.6 mmole m -2 d -1 for central basin sediments).