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Figur 1. The spatial distribution for CH4 flux (mmol/m-2d-1) in Lake Erssjön from late spring to early fall. The 22 measuring spots are interpolated using indirect IDW (invers distance weighting) in ArcMap, the darker blue the higher flux (>3.5 mmol/m-2d-1).

The CH4 fluxes changed over the seasons in Lake Erssjön. When Lake Erssjön was stratified (the five first measuring occasions, May to August) the fluxes were higher, and the flux decreased towards fall and the fall overturn. The spatial pattern in the lake showed that there were higher CH4 emissions close to the inlets at the North and South part of the lake and the inlets

Figure 2. Differences over time for log transformed CH4 flux (mmol/m-2d-1) 95 % confidens interval, for a) Lake Erssjön and Lake Följesjön and b) for diffusive and total emissions.

The CH4 flux in Lake Erssjön decreased after August (Figure 2a) similar to the spatial analysis and the profiles. The two last measurements (1 September and 22 September) were significantly lower compared to the first five measurements during May to August. In Lake Följesjön the pattern was slightly different, the measurement in 22 September was almost as high as the five measurements in May to August. Diffusive and ebullition emissions (ebullition with the diffusive flux included) from Lake Erssjön showed the same pattern as for the total flux, the measurements in September were lower than the initial measurements (Figure 2b)

Figure 3. The relationship between log transformed CH4 fluxes (ebullition and diffusion) and temperature(a) or depth (b) in Lake Erssjön.

The ebulltion emissions showed a significant positive correlation with water temperature (Figure 5, p< 0.001, R2=0.163). Diffusive CH4 flux also had a  signficant positive correlation with temperature (Figure 5, p<0.001 , R2=0.673). As for CH4 flux and depth dependence, the total CH4 flux was negative correlatae with depth (Figure 5, p= 0, R2=0.229). However the diffusive CH4 flux did not change with the depth (Figure 5, p=0.318 , R2=0.000).

Responsible for this page: Agneta Johansson
Last updated: 05/26/15