Biogeochemical and physical controls on methane fluxes from two ferruginous meromictic lakes

Data was collected at Brownie Lake in Minneapolis, MN, USA and at
Canyon Lake in the Upper Peninsula of MI, USA. The methane flux, or
the amount of methane entering the atmosphere over a given area per
time, was assessed at Brownie Lake and Canyon Lake. Sampling of
Brownie Lake during geochemical characterization revealed that the
methane flux out of the lake was much higher than Canyon Lake, as well
as other ferruginous meromictic lakes used as geochemical analogs for
early Earth’s ferruginous oceans. The dataset here was used to discern
why the methane flux out of Brownie Lake was high. Brownie Lake was
sampled in May, July and September of 2017 and June 2018. Canyon Lake
was sampled in June and September 2017 and May 2018. We used various
limnological probes and sensors (LDO sensor, Hydrolab multiprobe) to
collect water column profiles (temperature, dissolved oxygen, specific
conductance, chlorophyll a, pH). We also analyzed water samples
(cations, anions, CH4, DIC) using ion chromatography and ICP-MS and
measured isotopes (CH4, DIC) utilizing isotope ratio mass
spectrometry. The methane flux was constrained in two ways: taking
direct samples from the surface of each lake using floating static
flux chambers, which were measured by gas chromatography, and
estimated from geochemical reaction-transport modeling based on the
diffusional profiles of methane and other dissolved species throughout
the water column.