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Carbon dioxide variation in a Swedish lake measured with high temporal and spatial resolution


Lakes play an important role in the global carbon cycle but the mechanisms that control global evasion of CO2 are not well known. Here seasonal, diel and spatial variations in CO2 and the driving mechanisms for the variation, was investigated from May to September in a small Swedish forest lake using CO2 sensors. Comparative measurements were done in an adjacent forest lake, more similar to a wetland. Respiration was dominating in both lakes, which strongly regulated CO2 flux and partial pressure of CO2 (pCO2). This resulted in the lakes functioning as carbon sources, emitting substantial amounts of CO2 into the atmosphere. There was a seasonal variation with higher flux and pCO2 at the end of the growing season when stratification was released. The diel variation showed an increase in pCO2 during the dark period as a result of respiration. As for the spatial variation, there was a tendency for higher concentrations of pCO2 close to the lake inlets. This suggests that terrestrially derived carbon was transported into the lake. The pCO2 correlated negatively with water temperature and O2 concentration, and positively with air pressure. The flux was as well negatively correlated with O2, but correlated positively to air pressure and wind speed. Explanations for this can be that warmer waters stimulated the primary production which consumed CO2, and that the temperature naturally dropped towards the autumn. More unstable, windy weather conditions with lower air pressure favored flux release, suggesting a decreased pCO2 concentration in the water.   

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Last updated: 05/22/15