METHANOGENESIS IN SALT-MARSH SOILS OF THE NORTH-SEA COAST OF GERMANY

Temperate saltmarshes are a potential source of atmospheric methane. W e have measured the concentration and emission of methane in typical s altmarsh soils (Salic Fluvisols) and humus-rich saltmarsh soils (Thion ic Fluvisols) from the German North Sea coast. We also measured the me thane production rates of the latter. The methane content of typical s altmarsh soils reached 12.0 mu mol l(-1), although values of 1-4 mu mo l l(-1) were usual. The sulphate concentrations of the pore-water were about 10 mM, which means sulphate reduction is not limited and methan ogenesis would be suppressed. Methane concentrations were generally la rgest in summer. Independent of the redox potential and the degree of soil development, methane concentrations were smallest in those soils poorest in humus. Methane emission rates were almost zero. In the humu s-rich saltmarsh soils, methane concentrations were roughly a thousand times larger than those in typical saltmarsh soils, reaching values o f 23 mmol l(-1). The sulphate concentrations of the pore-water were of ten less than 1 mM, indicating limited sulphate reduction. Methane pro duction was up to 80 mu g cm(-3) day(-1) and was not inhibited when we added sulphate. Methane emission rates reached up to 190 mu g m(-2) d ay(-1) in summer, with values up to 20 mu g m(-2) day(-1) at other tim es. The two kinds of saltmarsh soil behave quite differently: the typi cal saltmarsh soils act as a sink for methane; the humus-rich saltmars h soils are a source.