Passive sampling method for high‐resolution concentration and isotopic composition of dissolved methane in A rctic lakes

Lakes are important sources of methane (CH 4 ), accounting for 6–16% of natural global CH 4 emissions annually. Vertical spatial resolution of CH 4 sampling in the water column of lakes is limited because of physical dimensions of sampling devices and sampling‐induced mixing. To improve pool‐size estimates of carbon, diffusive flux calculations for CH 4 , and detailed mechanistic understanding of CH 4 dynamics in lakes, more precise vertical profiles of dissolved gases through the water column are vital. We investigate the use of commercially available passive diffusion bags (PDBs) to obtain highly resolved (0.5‐m increments) vertical profiles of dissolved CH 4 concentrations and isotopic composition ( δ 13 ). Laboratory experiments determined PDB equilibration time was between 5 d and 9 d for both CH 4 concentration and δ 13 . During July 2013, PDBs were deployed at intervals of 0.5‐m depth for 5 d in two lakes located