Abstract
Due to the limited water exchange, lagoons are particularly prone to eutrophication. The consumption of oxygen in this process, coupled with simultaneous enrichment of bottom sediments with organic matter, reinforces the occurrence of anaerobic conditions and methanogenic growth. Methanogenic archaea activities cause depolymerization of organic compounds accumulated in sediments. As a result of such ecosystem transformation, methane might be produced and emitted from this basin. Chemical studies conducted in 2010 were focused on methane content in the surface bottom sediments in the Polish part of the Vistula Lagoon. The results showed that the highest methane concentration occurs in the southwestern part of this basin (6.45 mmol dm-3), while the lowest one in the southeastern part (7.1 × 10-3 mmol dm-3). Molecular studies were focused on specific methanogenic archaea gene identification. The comparison of nucleotide sequences of “mcrA gene” clones obtained from genomic DNA isolated from the Vistula Lagoon sediments indicates a similarity to the yet uncultivated archaea, but also to archaea from the Methanosarcinales and Methanomicrobiales orders.