Long-term direct CO2flux measurements over a boreal lake: Five years of eddy covariance data

1 Significant amounts of terrestrial carbon are processed in lakes and emitted into the atmosphere as CO2. However, due to lack of appropriate measurements the absolute role of lakes in the landscape as sinks or sources of CO2 is still uncertain. We conducted the first long-term, ecosystem-level CO2 flux measurements with eddy covariance technique in a boreal lake within a natural-state catchment covering 5 years. The aim was to reveal the natural level of CO2 flux between a lake and the atmosphere and its role in regional carbon cycling. On average, the lake emitted ca 10% of the terrestrial net ecosystem production of the surrounding old-growth forest and the main immediate drivers behind the fluxes were physical rather than biological. Our results suggest that lakes are an integral part of terrestrial carbon cycling.