Seasonal dynamics of carbon dioxide and methane in two clear-water lakes and two bog lakes in northern Wisconsin, U.S.A.

We investigated carbon dynamics in the water column and CO 2 and CH 4 exchange across the air-water interface in four closed-basin lakes in northern Wisconsin: two with clear, low dissolved organic carbon (DOC) waters and two bog lakes with stained, high-DOC waters. Clear-water lakes quickly became undersaturated following ice-out and remained undersaturated until fall turnover. Bog lakes were supersaturated in CO 2 throughout the ice-free season, although surface CO 2 concentrations dropped sharply following ice-out and increased again during autumn turnover. Differences in seasonal patterns of CO 2 were attributed to morphometry and the timing and intensity of mixing events. Ice-free season fluxes of CO 2 were 6.7 and 10.0 mol·m -2 in the bog lakes and 1.2 and 0.09 mol·m -2 in the clear-water lakes. Fluxes of CH 4 were significant only immediately after ice-out and during autumn turnover and were <0.4 mol·m -2 in the bog lakes and <0.05 mol·m -2 in the clear-water lakes. Compared with changes in carbon pools in the lakes, our results indicate rapid carbon turnover rates in bog lakes, as opposed to clear-water lakes. We suggest that allochthonous inputs of CO 2 may be responsible for this rapid turnover.