A new paper discusses the climate gas nitrous oxide (N₂O) in boreal lakes, using data from 112 lakes in Finland. Lakes and streams act as recipients of carbon, nitrogen, and other nutrients transported from land, but also contribute to landscape greenhouse gasses (GHG) by emitting carbon dioxide, methane, and nitrous oxide (N₂O). Freshwater N₂O has received much less interest compared to the carbon gases, and is therefore less understood. Up-scaling of freshwater N₂O emissions at regional to global scales has remained challenging due to sparse data; often based only on summer measurements.

The authors collected seasonal data on N₂O concentrations from 112 randomly selected boreal lakes in Finland. The data analyses underlined the key role of nitrate in regulating seasonal and spatial N₂O concentrations. Nitrate explained 78 % of the variation in N₂O in all lakes. The Global Warming Potential of N₂O in the data was 35 % of that of diffusive CH₄ emissions, underlining the importance to include N₂O in landscape greenhouse gas estimates.

The data also demonstrated large seasonal variation of nitrate and N₂O in boreal lakes and the important role of winter in annual emission estimates, the neglect of which results in underestimation of annual N₂O flux estimates. During recent mild winters, the ice cover period has been shorter and warm autumns have delayed the freezing day. Assuming one month shorter ice cover period resulted in 15% larger evasion estimates.

Kortelainen, P, Larmola, T, Rantakari, M, Juutinen, S, Alm, J, Martikainen, PJ. Lakes as nitrous oxide sources in the boreal landscape. Glob Change Biol. 2020; 00: 1– 14. https://doi.org/10.1111/gcb.14928