Bacterial biogas production in coastal systems affected by freshwater inputs

Abstract

The concentrations of two greenhouse gases, nitrous oxide (N 2O) and methane (CH 4), and the bacterial processes involved in their production (nitrification and denitrification for N 2O, and methanogenesis for CH 4), were determined in surface waters of two coastal areas under the influence of freshwater inputs, on one part in the Gulf of Lions and the Rhone River plume, in northwestern Mediterranean Sea, and on the other part in the inner Thermaikos Gulf, in Aegean Sea, eastern Mediterranean Sea. High concentrations of dissolved CH 4 and N 2O were recorded in the surface waters of Gulf of Lions and Gulf of Thermaikos, up to 1300 nM for CH 4, and 40 nM for N 2O. No direct relationship could be found between the concentration and production of the biogases, as they may also be produced in deep water or bottom sediment in shallow areas, or derived from anthropogenic activity or ship contamination in polluted areas. Irrespective of the origin of CH 4 and N 2O, the presence of extremely high concentrations of these two gases in superficial seawater implies that they can easily escape to the atmosphere; consequently, these nearshore waters enriched in greenhouse gases may play an important role in the increase in atmospheric concentration of both CH 4 and N 2O.