Emissions of methane from temperate artificial reservoirs – what is already known

Methane is assumed to belong to the most  important greenhouse gases, however factors affecting methane production and emission are still not satisfactory elucidated. Artificial reservoirs which are critical resources to obtain water and hydropover in many countries are  one of the methane sources which received only limited attention so far.   We reviewed existing information about methane emissions from them.  Emissions  are combination of diffusion, ebullition and degassing under dam, but not all pathway must be presented. Nineteen studies, mainly from North America and Europe were compared, Only small portion of the studies was focusing on all pathways of methane release. Spatio-temporal variability, which is especially high for ebullition (ebullition is probably responsible for the most of the methane emissions), was covered in 3 reservoirs only. For this purposes is newly used acoustical method good tool, hydroacoustics cover mainly spatial variability of ebullition, which is poorly couth by traditional bubble traps. The most of the  studies was performed in summer period only and for low number of localities.  Future studies should use more uniform design covering better all potential pathway of methane emissions and  taking care of spatio-temporal variability of ebullition.  More systematic studies covering effect of climate and landscape variables as well as reservoir properties (morphology management etc.) are needed.