Methane (CH4) is a greenhouse gas that has increased rapidly in the atmosphere since the industrialization. An often forgotten, yet important source of CH4 is lakes, but the factors controlling the emissions are not fully known. From lakes, CH4 can reach the atmosphere in three ways; diffusion, ebullition (i.e bubble flux from sediments) and via transport through emergent aquatic plants. This study aimed to 1) find out how CH4 emissions change spatially and temporally within a lake, 2) how the proportion of ebullition and diffusion can be explained and 3) if CH4 emissions change over time in two adjacent lakes. CH4 emissions were measured every third week from May to September for 24 or 48 hours using floating chambers positioned along depth dependent transects. Weather and water chemistry (water temperature, oxygen, pH, phosphorus and nitrogen etc.) was measured as potential explanatory factors. CH4 emissions changed over time (from late spring to fall), in one lake the CH4 emissions were higher during late spring and summer than after the fall overturn. In addition, CH4 emissions were strongly positively correlated with water temperature and correlate negatively with depth. Shallow and small lakes warm up faster and many small lakes can have a greater impact on the total emissions than one large. Small changes, in local conditions but also large scale changes could have a huge impact on the CH4 emissions from lakes. Increasing temperature caused by the greenhouse effect could cause an increase in CH4 emissions from lakes.
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Last updated: 10/20/15