Relationship between P(CO2) and dissolved organic carbon in northern Wisconsin lakes
We investigated the relationships between early summer partial pressures of CO2 (PCO2) and dissolved organic carbon (DOC) concentration in the surface waters of 27 northern Wisconsin lakes. Other variables we considered were the drainage ratio, lake area, lake depth and the extent of wetland in each drainage basin. PCO2 had a strong positive relationship with DOC concentration. There was a weak negative relationship between PCO2 and lake area, which was most apparent in lakes with DOC concentrations above 5 mg L-1. DOC concentration was positively correlated with the drainage ratio and wetland extent. We conclude that allochthonous C supplied by the drainage basin, particularly from areas of wetland, is a major factor determining CO2 saturation of these lakes and suggest that there are two complementary mechanisms by which this can occur. Higher PCO2 may result from higher in-lake respiration of the allochthonous organic carbon, and/or from inputs of surface waters from wetlands that are high in both DOC and CO2.