Towards a more comprehensive understanding of lacustrine greenhouse gas dynamics — two-year measurements of concentrations and fluxes of CO2, CH4 and N2O in a typical boreal lake surrounded by managed forests

摘要

Lakes emit terrestrially fixed carbon back to the atmosphere as carbon dioxide (CO2) and methane (CH4). Redox conditions in the water columns of lakes typically vary seasonally, and therefore lakes may also be sources of nitrous oxide (N2O). In this study, we measured the weekly water column concentrations of CO2, CH4 and N2O in a boreal lake and calculated the annual emissions of these gases for the years 2011 and 2012. We found that the emissions of all the gases studied were high right after the ice melt, CH4 most likely originating from the catchment. Bottom anoxia in summer induced maximum concentrations of CH4 and N2O near the sediment, but only elevated the emission of N2O in autumn 2012. Otherwise, the high concentrations near the sediment did not affect the surface concentrations. The unstable water column in summer 2012 increased the CO2 and N2O emissions, but prevented anoxia, and thus decreased the CH4 concentrations. From the perspective of global warming, the CO2 emissions were by far the most significant and the relevance of the N2O emissions was negligible.