Methane release from wetlands and watercourses in Europe

This study was conducted to estimate annual CH4 efflux from wetlands and watercourses in Europe and some adjacent areas. Wet ecosystems were divided into seven categories: ombrotrophic mires, minerotrophic mires, freshwater marshes, saltwater marshes, small lakes, large lakes and rivers. The geographical distribution and total area coverage for each of these respective ecosystems were taken from CORINE 2000, Global Land Cover 2000 [JRC, 2003. Harmonisation, mosaicing and production of the Global Land Cover 2000 database (Beta Version). EUR 20849 EN, Joint Research Center, Ispra, Italy] and ESRI 2003 databases. CH4 release factors were obtained from an extensive overview of published literature. Less than 3% of the study area of 22,560,000 km2 consisted of wetlands and watercourses. Large lakes (40%), minerotrophic mires (24%) and ombrotrophic mires (20%) covered almost 85% of the total area of wetlands and watercourses. The total CH4 release from European wetlands and watercourses was estimated to be 5.2 Tg a-1. CH4 release from minerotrophic mires (48%), large lakes (24%), and ombrotrophic mires (12%) composed most of the total CH4 efflux. High variation in the rate of CH4 release within the main ecosystem types, small number of studies in some ecosystems and ecologically inadequate land-cover classification are the main reasons for the uncertainties of the estimate. A better estimation of European CH4 effluxes from natural sources, now and future, would require: a much more detailed and ecologically relevant mapping of the area of different types of wetlands and watercourses, and long-term measurements of CH4 fluxes and their controlling environmental factors in poorly studied types of wetlands and watercourses. Finally, the data could be used for dynamic modelling of CH4 fluxes in the current and changing environmental conditions.