Carbon quality and quantity in lake sediments and their relationship with pore-water and lake-water methane among lakes of the Mackenzie River Delta, Western Canadian Arctic

Sediment cores were taken from lakes in the Mackenzie Delta to assess how carbon-content in the lake sediments, and their dissolved organic matter (DOM) quantity and quality, affects methane (CH4) concentrations in the pore-waters and lake-waters. Cores were taken just before ice-out (34 lakes), then bi-weekly (6 lakes) until late open-water, in combination with CH4 oxidation (MOX) measurements at the sediment-water interface. Fluorescence components derived from Parallel Factor Analysis of pore-water DOM (four under-ice, six open-water) revealed carbon-quality patterns related to river-to-lake connection times and pore-water CH4. Pore-water CH4 was lower concentration and less depleted in 13C in near-surface relative to deeper sediments. Anaerobic electron-acceptor concentrations were well-related to near-surface CH4 concentrations, but varied by lake, whereas DOM-quality measures were more strongly related to pore-water CH4 at deeper depths. MOX rates ranged from 2.72 to -0.19 umol CH4 m-3 s-1 and were related to CH4 substrate concentrations and sediment-N content.