Dissolved methane during hypoxic events at the Boknis Eck Time Series Station (Eckernf rde Bay, SW Baltic Sea)

Dissolved CH4 was measured in the water column at the Boknis Eck (BE) time series station in the Eckernf rde Bay (SW Baltic Sea) on a monthly basis from June 2006 to November 2008. The water column at BE was always supersaturated with CH4 and, therefore, CH4 was released to the atmosphere throughout the sampling period. A flux estimate indicates that the atmospheric CH4 emissions are balanced by the CH4 flux from the sediment. We did not detect a straightforward relationship between periods of enhanced CH4 in the bottom layer and hypoxic events at BE: The sedimentary release of CH4 seemed to be mainly triggered by sedimenting organic material from phytoplankton blooms. We conclude that future CH4 emissions from BE will be determined by both the occurrence and the intensity of phytoplankton blooms, which in turn will be influenced by eutrophication. However, hypoxic events seem to have only a modulating effect in the way that they enhance sedimentary methanogenesis.