Small lakes in northern latitudes represent a significant source of CH4 to the atmosphere that is predicted to increase with warming in the Arctic. Yet, whole-lake CH4 budgets are lacking as are measurements of δ13C-CH4 and δ2H-CH4. In this study, we quantify spatial variability of diffusive and ebullitive fluxes of CH4 and corresponding δ13C-CH4 and δ2H-CH4 in a small, Arctic lake system with fringing wetland in southwestern Greenland during summer. Net CH4 flux was highly variable, ranging from an average flux of 7�mg CH4 m−2 d−1 in the deep-water zone to 154�mg CH4 m−2 d−1 along the lake margin. Diffusive flux accounted for�~8.5�% of mean net CH4 flux, with plant-mediated and ebullitive flux accounting for the balance of the total net flux. Methane content of emitted ebullition was low (mean���SD 10���17�%) compared to previous studies from boreal lakes and wetlands. Isotopic composition of net CH4 emissions varied widely throughout the system, with δ13C-CH4 ranging from −66.2 to −55.5�‰, and δ2H-CH4 ranging from −345 to −258�‰. Carbon isotope composition of CH4 in ebullitive flux showed wider variation compared to net flux, ranging from −69.2 to −49.2�‰. Dissolved CH4 concentrations were highest in the sediment and decreased up the water column. Higher concentrations of CH4 in the hypoxic deep water coincided with decreasing dissolved O2 concentrations, while methanotrophic oxidation dominated in the epilimnion based upon decreasing concentrations and increasing values of δ13C-CH4 and δ2H-CH4. The most depleted 13C- and 2H-isotopic values were observed in profundal bottom waters and in subsurface profundal sediments. Based upon paired δ13C and δ2H observations of CH4, acetate fermentation was likely the dominant production pathway throughout the system. However, isotopic ratios of CH4 in deeper sediments were consistent with mixing/transition between CH4 production pathways, indicating a higher contribution of the CO2 reduction pathway. The large spatial variability in fluxes of CH4 and in isotopic composition of CH4 throughout a single lake system indicates that the underlying mechanisms controlling CH4 cycling (production, consumption and transport) are spatially heterogeneous. Net flux along the lake margin dominated whole-lake flux, suggesting the nearshore littoral area dominates CH4 emissions in these systems. Future studies of whole-lake CH4 budgets should consider this significant spatial heterogeneity. � 2016, Springer International Publishing Switzerland.
School of Public and Environmental Affairs, Indiana University, Bloomington, IN, United States; Department of Geological Sciences, Indiana University, Bloomington, IN, United States
Recommended Citation:
Thompson H.A.,White J.R.,Pratt L.M.,et al. Spatial variation in flux, δ13C and δ2H of methane in a small Arctic lake with fringing wetland in western Greenland[J]. Biogeochemistry,2016-01-01,131(2018-01-02)