Separating contributions from natural and anthropogenic sources in atmospheric methane from the Black Sea region, Romania

The Danube Delta-Black Sea region of Romania is an important wetland, and this preliminary study evaluates the significance of this region as a source of atmospheric CH4. Measurements of the mixing ratio and δ13C in CH4 are reported from air and water samples collected at eight sites in the Danube Delta. High mixing ratios of CH4 were found in air (2500–14,000 ppb) and dissolved in water samples (∼1–10 μmol L−1), demonstrating that the Danube Delta is an important natural source of CH4. The intercepts on Keeling plots of about −62‰ show that the main source of CH4 in this region is microbial, probably resulting primarily from acetate fermentation. Atmospheric CH4 and CO data from the NOAA/ESRL (National Oceanic and Atmospheric Administration/Earth System Research Laboratory) were used to make a preliminary estimate of biogenic CH4 at the Black Sea sampling site at Constanta (BSC). These data were used to calculate ratios of CH4/CO in air samples, and using an assumed CH4/CO anthropogenic emissions ratio of 0.6, fossil fuel emissions at BSC were estimated. Biogenic CH4 emissions were then estimated by a simple mass balance approach. Keeling plots of well-mixed air from the BSC site suggested a stronger wetland source in summer and a stronger fossil fuel source in winter.