Seasonal dynamics of carbon dioxide and methane in two clear-water lakes and two bog lakes in northern Wisconsin, USA

We investigated carbon dynamics in the water column and CO2, and CH4 exchan ge across the air-water interface in four closed-basin lakes in northern Wi sconsin: two with clear, low dissolved organic carbon (DOC) waters and two bog lakes with stained, high-DOG waters. Clear-water lakes quickly became u ndersaturated following ice-out and remained undersaturated until fall turn over. Bog lakes were supersaturated in CO2 throughout the ice-free season, although surface CO2 concentrations dropped sharply following ice-out and i ncreased again during autumn turnover. Differences in seasonal patterns of CO2 were attributed to morphometry and the timing and intensity of mixing e vents. Ice-free season fluxes of CO2 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 CH4 w ere significant only immediately after ice-out and during autumn turnover a nd were <0.4 mol.m(-2) in the bog lakes and <0.05 mol.m(-2) in the clear-wa ter lakes. Compared with changes in carbon pools in the lakes, our results indicate rapid carbon turnover rates in bog lakes, as opposed to clear-wate r lakes. We suggest that allochthonous inputs of CO2 may be responsible for this rapid turnover.