Limnol. Oceanogr. Lett. (2019).

Lake productivity will increase with warmer temperatures. Biomass breakdown increases CO2 emissions to the atmosphere, relative to carbon burial into lake sediments. At the same time as warming, lakes losing transparency (via increased nutrients and organic runoff), and how this interacts with warming to affect carbon emission and burial, is unclear.

To address this, Maciej Bartosiewicz, of the University of Basel, and co-authors consider observational data, alongside output from a 1D model. These are extrapolated to predict potential emissions and burial for temperate and boreal lakes.

They find that stratification causes lakes to warm at the surface but remain cold at depth, reducing respiration and increasing sediment carbon storage. For shallow lakes, additional burial could store up to 4.5 Tg C yr−1, 9% more than current estimates. But reduced mixing causes anoxic conditions at depth, resulting in greater methane production (8% increase). These effects result in an overall net increase of 8 Tg CO2e yr−1, as methane has a greater warming potential, highlighting the need to look at the whole picture when considering warming effects.