Ackumulation av CO2 och CH4 i istäckta boreala sjöar : Hur förändras ackumulationen i sjöar påverkade av avverkning jämfört med referenssjöar?

The aim of this report was to quantify the accumulation of carbon dioxide (CO2) and methane (CH4) in ice-covered lakes in winter (October-March) during three consecutive years, and to assess whether the concentrations of DIC and CH4, as well as the ratio DIC:CH4 differs between years and between lakes affected by clearcutting and untreated reference lakes. Water- and gas samples were collected from four boreal lakes (two affected by clearcutting and two untreated reference lakes) located in Västerbottens inland in spring. The lakes were found to accumulate on average 91, 55, and 84 mgCm-2d-1 during winters 2012-2013, 2013-2014, and 2014-2015, mostly originating from CO2. The concentrations of DIC (autumn and spring) were higher in the affected clear-cut lakes compared to reference lakes for all years, including the reference year (2012-2013) before clear-cutting. No such difference was found for CH4 or the ratio DIC:CH4. Accumulated concentrations of CO2 and CH4 varied between years while the ratio (accumulated) CO2:CH4 increased over time for all lakes but with no difference between the clear-cut lakes and the reference lakes. The differences between the clear-cut and the reference lakes, hence, are unclear with differences between years likely stemming from natural variations. The effects of clearcutting in catchment areas might be more visible at other times of year not seen in this study which focuses only on winter. The amount of CO2 and CH4 accumulated under ice in lakes was substantial i.e. high-lighting the importance of including winter accumulation of greenhouse-gases in estimations of yearly emissions from lakes