Summertime fluxes of N2O, CH4 and CO2 from the littoral zone of Lake Daming, East Antarctica: effects of environmental conditions

Nitrous oxide (N2O), methane (CH4) and carbon dioxide (CO2) fluxes were investigated from the algal-rich littoral zone of Lake Daming, East Antarctica during the summers of 2008/09 and 2009/10, using a static chamber technique. High N2O emissions occurred in the littoral zone with the mean flux range of 0.19–7.11 μmol N2O m-2 h-1. The mean CH4 fluxes ranged from 2.51–5.32 μmol CH4 m-2 h-1, and they were significantly affected by the lake thermal regime. There were significant differences (P < 0.05) in CH4 and N2O fluxes under the light and dark conditions, and sunlight greatly increased N2O emissions by stimulating the algal photosynthesis, but decreased CH4 emissions. Overall the littoral zone represented a weak CO2 sink with the mean flux range of -0.37–0.13 mmol CO2 m-2 h-1. The mean ecosystem respiration and photosynthesis rates varied from 0.47–2.90 mmol CO2 m-2 h-1 and from -0.33 to -2.63 mmol CO2 m-2 h-1. The combined global warming potential (GWP) of N2O and CH4 fluxes completely counteracted and surpassed CO2 uptake by the algal photosynthesis, and high GWP-positive of N2O and CH4 emissions might convert an algal-rich lake site with a net CO2 uptake into a net radiative forcing source during the ice-free period.