AbstractsEarth & Environmental Science

Dinitrous oxide (N₂O) is a potent greenhouse gas some 354 times stronger than carbon dioxide (CO₂) in the atmosphere. Recent studies show that lake denitrification contributes to a considerable part of the global N₂O emissions. Despite this, lake-N₂O emissions are not being accounted for in global greenhouse gas modeling because it has not yet been accurately understood and quantified. The aim of this study was to assess how denitrification varies between and within boreal lakes and how it is controlled by nitrate- (NO₃) and carbon (C) availability and temperature. Studies on denitrification were performed using the acetylene inhibition technique on sediments from three lakes in northern Sweden (February to August, 2014). Results showed that denitrification was correlated (linear regression, r²=0.71) with NO₃ concentrations in the hypolimnion water at ambient conditions and that additions of NO₃ up to a concentration of 50 µg NO₃-N L^-1increased denitrification. Temperature increased denitrification in all lakes, at all sites except in one lake in July, when nutrient concentrations were at its lowest. The spatial and temporal variation in denitrification was small at ambient conditions (1-3 µmol N₂O m^-2 h^-1)but the variation in the response to nutrient additions and temperature increase was very high. This was in part attributed to differences in dissolved organic C (DOC). These findings have important implications for future denitrification research and how lake-N₂O production is included in greenhouse gas modeling and contributes to our knowledge on how northern boreal lakes may respond to enhanced nutrient loadings and global warming.