Interannual variation and climatic regulation of the CO₂ emission from large boreal lakes

We studied the interannual variation of surface water partial pressure of CO 2 ( p CO 2 ) and the CO 2 emissions from the 37 large Finnish lakes linking them to the water quality, catchment and climate attributes in 1996–2001. The lake water CO 2 was measured three times a year in the study lakes in 1998 and 1999 and for the rest of the years the CO 2 was modeled by measured alkalinity. The median annual CO 2 emission to the atmosphere ranged between 1.49 and 2.29 mol m −2 a −1 . The annual CO 2 emission followed closely the annual precipitation pattern with the highest emission during the years when the precipitation was highest ( r 2 =0.81–0.97, P <0.05). There was a strong negative correlation ( r 2 =0.50–0.82, P <0.001) between O 2 and CO 2 saturation in the lake water during stratification suggesting effective decomposition of organic matter in the lakes. Furthermore, total phosphorus and the proportion of agricultural land in the catchment had significant positive correlations with CO 2 saturation.