RELATIVE CONTRIBUTIONS OF HYPOXIA AND NATURAL GAS EXTRACTION TO ATMOSPHERIC METHANE EMISSIONS FROM LAKE ERIE

Reduced oxygen availability in lakes due to summer stratification events can contribute to atmospheric methane emissions, and Lake Erie has a persistent low oxygen event in bottom waters during late summer. Lake Erie also has substantial subsurface natural gas deposits that are currently being extracted from areas in Canadian waters. We hypothesized that the lake would be a source of methane to the atmosphere in late summer, prior to fall turnover, and that natural gas wells and pipelines would contribute to additional methane emissions from resource extraction areas in Canadian waters.

Sampling was conducted at a total of 21 sites in central and western Lake Erie during early September, 2012. Sites were selected to collect samples from a wide range of environmental conditions in order to better establish the baseline flux from these areas. We selected an array of sites in the offshore environment, sites from a very shallow bay and sites within the Canadian gas fields. Air samples were gathered using floating flux chambers tethered to the research vessel. Dissolved gas water samples were collected using a Van Dorn bottle.

Preliminary results show a consistent but small flux of methane throughout the lake, with flux rates adjacent to natural gas pipelines about an order of magnitude greater than elsewhere. Samples are currently being analyzed for stable isotope ratios of methane, which can distinguish between fossil fuel and biological sources of methane.

This project has two goals; first it is an effort to constrain the global warming potential of hypoxia in the Great Lakes, and secondly it is an attempt to constrain fugitive emissions of methane from resource extraction areas within Lake Erie. These two sources of methane may contribute to increased greenhouse gas emission rates regionally, and fugitive methane is taking on increased importance due to the expansion of natural gas extraction activities in Lake Erie.