B41C-0451
Internal Methane Cycling in a Small Temperate Lake

Thursday, 17 December 2015
Poster Hall (Moscone South)
Shoji Devasia Thottathil, University of Quebec at Montreal UQAM, Montreal, QC, Canada
Abstract:
Despite the ubiquitous methane (CH4) supersaturation in lakes, mechanistic understanding on the internal CH4 cycling that regulate the annual CH4 emission from these systems remains unresolved. Multi-year measurements on vertical and horizontal variability in CH4 concentration and isotopic (δ13C) signature, along with the estimates on the rates of air-water and sediment CH4 flux from a small temperate lake (Lake Croche, South eastern Quebec, Canada) were used to reconstruct the internal CH4 cycling in the northern temperate lakes. While flux from hypolimnetic sediments was the largest source of water column CH4, strong, but seasonally varying CH4 oxidation zone separated the CH4-rich hypolimnion from surface layer. The diffusive oxygen (O2) supply from the upper layers regulated the oxidation zone, upward expansion and storage of CH4 in the deeper water column. Despite the strong oxidation-filter, surface water CH4 always exceeded the atmospheric equilibrium and concentrations were varied over the space and time. Lateral advection from the epilimnetic sediments and sporadic entrainment from the sub-surface CH4 maxima mostly explains the surface CH4 variability during stratified period. Air-water exchange was a relatively larger sink than the oxidative loss of CH4 in the surface layers. Using a mass-balance approach, we reconstruct the processes regulating annual CH4 emission from northern temperate lakes.