Methane flux from sediment into near-bottom water and its variability along the Hel Peninsula—Southern Baltic Sea

• Methane flux from sediment into near bottom water varied yearly and seasonality.
• Flux fluctuation connected to water dynamics and temperature.
• Benthic chambers method is suitable for methane flux determination.

Methane in the sediments of the Bay of Puck occurs in the form of free gas bubbles and is released from the sediments into near-bottom water in the form of a flux. The sediments of the Bay of Puck also contain methanogens whose biological activity results in the production of methane. Research carried out in the coastal areas of the bay along the Hel Peninsula proved the existence of a methane flux ranging from 0.81 mmol m−2 d−1 to 33.41 mmol m−2 d−1 in 2011, while in 2010 ranged from 0.91 mmol m−2 d−1 to 49.15 mmol m−2 d−1. Seasonal and annual fluctuations were also observed. Other factors contributing to the change in methane flux are water temperature and other environmental factors. An increase in temperature causes an increase in the flux. Fluctuations of the flux within individual sampling sites were also observed. A test performed with specific methanogenic inhibitor—sodium dodecyl sulfate (SDS) unexpectedly revealed higher methane concentrations (10–13%) in samples to which SDS was added. We speculate that these higher methane concentration result from the lysis of methane-forming bacteria cells when exposed to SDS.