Report for methane monitoring in Arctic Lakes in Northwest Territories, Canada, March 2016

The primary goal of fieldwork in spring 2016 was the deployment of OsmoSampler units in two of the project study lakes near Inuvik (region 3 in Figure 1, specifically Lakes 129 and 520), to
capture the ice-out period in higher temporal resolution. A secondary goal was the collection of
under-ice water samples for calibrating the OsmoSampler methane, ion, and microbiology data. The goal of the annual OsmoSampler deployments from August 2015 is to capture of a
continuous annual record of lake biogeochemistry, including under ice cover, to determine the
source, cycling, and fate of methane in these Canadian Arctic lakes. To this end, each
OsmoSampler system contains three different samplers, as well as a suite of sensors. The three
samplers are for methane ("CH4"), major/minor/trace elements ("Acid"), and microbial
community composition ("BOSS"). The sensor suite includes one sensor for dissolved oxygen
and temperature, one sensor for pressure, and one sensor for light penetration. The purpose of the higher resolution OsmoSamplers for deployment during this fieldwork is to
collect a second record of methane and dynamics during the critical ice-out period, with a higher
sampling resolution to permit ~daily intervals.These OsmoSamplers also contain CH4 and Acid
samplers, with pumps that pull water into the samplers at a faster speed (i.e. 20-membrane
OsmoPumps instead of 8-10 membrane pumps in the annual deployments). Sensors were also
included in the deployments to collect additional records of dissolved oxygen, temperature,
conductivity, light penetration, and water level, with multiple temperature sensors to understand
under-ice temperature stratification. BOSS samplers were not included in these OsmoSampler
deployments, as the volume required for samples was not amenable to scaling up. To calibrate the OsmoSampler data, under-ice water samples were also collected immediately
after opening a hole in the ice, to determine dissolve methane and ion concentrations as well as
lake microbial community composition.