Methane Emissions from Lakes and Reservoirs: Uncertainties Due to the Formation and Break-up of the Ice Cover

Methane is the second most potent greenhouse gas (GHG) in the earth’s atmosphere contributing to global warming (after carbon dioxide). Freshwater bodies (lakes and reservoirs), being the most significant source of methane on a global scale, are distributed over the earth’s surface in such a way that the bulk of them is covered with ice for several months of the year. During the freeze-up, the water column is isolated from the atmosphere, so methane emissions cease or become restricted to open holes and cracks in the ice cover. Methane accumulated both under ice and within ice-trapped gas bubbles is released at spring ice melt. This review article examines in detail the ways methane is released from the bottom of seasonally ice-covered lakes and reservoirs and the mechanisms of methane accumulation in their water column and ice cover, as well as under-ice processes facilitating and impeding such an accumulation. Factors controlling methane emissions at spring ice melt and current approaches for estimating the magnitude of these emissions are also discussed. The data systematized in the article can be used for (1) planning field studies on seasonally ice-covered water bodies throughout winter and spring and (2) the development of process-oriented models that take into account the influence of ice cover on the spatiotemporal carbon dynamics of freshwater ecosystems and methane emissions from these ecosystems.