Methane cycling in the sediment and water column of mid-boreal hyper-eutrophic Lake Kevätön, Finland
Liikanen, Anu; Huttunen, Jari T.; Valli, Kaisa; Martikainen, Pertti J.
published: Aug 7, 2002
ArtNo. ESP141015404003, Price: 29.00 €
Methane (CH4) dynamics were studied in the sediments and the water column of mid-boreal, hyper-eutrophic Lake Kevätön, Finland. We determined the CH4 production and oxidation potentials in deep and shallow profundal sediments, water column CH4 oxidation potentials, and seasonal variation in CH4 oxidation in water column in situ. The sediment CH4 production and oxidation potentials were greater in summer than in winter. In the shallow profundal, the CH4 oxidation potential of the surface sediment was equal to or higher than the sediment CH4 production potential, whereas in the deep profundal sediment, CH4 production potential exceeded the CH4 oxidation potential. The entire water column had the potential to oxidize CH4. The CH4 oxidation rates (shown as negative values) in the water column in situ, ranged from 0 to -27 mmol m-3 d-1, and were lower than the potential CH4 oxidation rates, which ranged from -9 to -160 mmol m-3 d-1. The supply of CH4 regulated its oxidation rate in water in situ, resulting in a clear seasonal variation in the level of CH4 oxidation. The highest oxidation rates occurred in the hypolimnion during summer and winter stratifications when there were the highest CH4 concentrations. During these stratifications, the CH4 oxidation contributed significantly to the hypolimnetic O2 consumption. In winter, there was CH4 oxidation both in the aerobic and anaerobic water column. The depth integrated CH4 oxidation in the water column was highest during stratification, in winter -31 and in summer -15 mmol m-2 d-1. During the autumn overturn, the water column oxidized some CH4, but in spring, after the ice melt, the water column had a very low CH4 production. Oxidation of CH4 both in the sediments and water column reduced the emissions of CH4 to the atmosphere.