POSITIVE FEEDBACKS IN GLOBAL BIOGEOCHEMISTRY: METHANE EMISSIONS FROM FRESHWATER LAKES

Freshwater inland lakes are a significant source of atmospheric methane (CH₄), and despite covering less than 1% of the earth’s surface, lakes emit more CH₄ than the ocean. With freshwater lakes missing from many atmospheric circulation models, there is a need to quantify their potential climate impact. A positive feedback in the global climate has been observed, with CH₄ emissions from lakes increasing as lakes warm. The mechanism involves both an increased production of CH₄ in the littoral sediments, and increased diffusive efflux from warm surface water. Methane cycles in lakes were characterized over the course of a summer, and drivers of emissions were determined. Methane production, CH₄ storage, and lake surface area to volume ratio were determined to be reliable predictors of CH₄ emissions. Additionally, a strong correlation exists between lake productivity and emissions. This suggests that eutrophication may be an amplifier of existing global change mechanisms. Our findings have implications for both existing lakes in temperate and boreal zones, as well as newly forming glacial lakes and wetlands at higher latitudes.