Seasonal Methane Dynamics in Lakes of the Mackenzie River Delta, Western Canadian Arctic

Abstract

Methane (CH4) dynamics were investigated in lake-waters of the Mackenzie River Delta in 2014 and 2015 to estimate CH4 emissions and evaluate potential drivers of seasonal CH4 dynamics. Water-column CH4 and related variables were measured at end-of-winter and tracked through open-water in up to 43 lakes, plus water-column CH4 oxidation (MOX) and water-to-atmosphere emissions were measured in 6 lakes. Under-ice CH4 accumulations were high by end-of-winter, with levels in some lakes greater than 20 years prior. Water-column CH4 and carbon-quantity are positively related regardless of season, however, relationships between CH4 and carbon-quality are strikingly different between winter and open-water. CH4 is inversely related to pH, which, surprisingly, also negatively affects MOX. MOX is highest at ice-out and decreases over open-water. Based on areal-weighted fluxes, Mackenzie Delta lakes emitted 35.79 Gg of CH4, with 24% occurring at ice-out, and during open-water 50% and 26% respectively occurring via ebullition and diffusion.