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

In terms of contribution to global warming, methane is the second most potent greenhouse gas after carbon dioxide in the Earth’s atmosphere. 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 bulk of them is covered with ice for several months of the year. During the freeze-up, the water column is getting isolated from the atmosphere so that 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 of methane release from the bottom of seasonally ice-covered lakes and reservoirs, 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/spring period; 2) 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.