Quantifying emissions of methane derived from anaerobic organic matter respiration and natural gas extraction in Lake Erie

Abstract

Despite a growing awareness of the importance of inland waters in regional and global carbon (C) cycles, particularly as sources of the greenhouse gases carbon dioxide (CO2) and methane (CH4), very little is known about C sources and fluxes in the Laurentian Great Lakes, Earth's largest surface freshwater system. Here, we present a study of CH4 dynamics in Lake Erie, which has large spring algae blooms linked to fertilizer runoff and followed by hypoxia, as well as an extensive network of natural gas wells and pipelines in Canadian waters. Lake Erie is a positive source of CH4 to the atmosphere in late summer, even in shallow regions without water column hypoxia. Stable isotopic measurements indicate that both biogenic and thermogenic CH4 contribute to emissions from Lake Erie. We estimate that Lake Erie emits 1.3 ± 0.6 × 105 kg CH4‐C d−1 in late summer, with approximately 30% of CH4 derived from natural gas infrastructure. Additional work is needed to determine the spatial and temporal dynamics of CH4 emissions from Lake Erie and to confirm estimates of source contribution. Studies of the C cycle in large lakes are not as straightforward as those in smaller lakes, as, in addition to O2 availability, subsurface currents and high winds may exert significant control over dissolved CH4 patterns. If climate warming and increasing precipitation intensity lead to increased algal biomass and/or greater extent and duration of hypoxia, this may increase emissions of CH4 from Lake Erie in a positive feedback to climate change.

Methane Feedbacks to the Global Climate System in a Warmer World

“…Such shifts in the zones of CH 4 production and oxidation due to increased organic matter input can occur on timescales of years (Egger et al, 2015;Rooze et al, 2016) or seasons (Crill & Martens, 1983;Gelesh et al, 2016;Martens et al, 1986) and may increase the potential for release of CH 4 from sediments to overlying water and the atmosphere (Crill & Martens, 1983;Gelesh et al, 2016). High temporal resolution observations are needed to quantify CH 4 release to the atmosphere from seasonally hypoxic systems and to identify the key controlling factors (e.g., the role of wind and storms and the breakdown of stratification) (Gelesh et al, 2016;Townsend-Small et al, 2016). Both temperature-driven increased CH 4 emissions from northern freshwater lakes and from coastal waters have the potential to provide a positive feedback on a warming climate, with the former areas being quantitatively most important (Borges et al, 2016;Wik et al, 2016).…”

Methane Sources in the Waters of Lake Michigan and Lake Superior as Revealed by Natural Radiocarbon Measurements

“…Surface CH 4 concentrations ranged from 3.5 to 60 nM (Figure a) in these two lakes. Concentrations in Lakes Michigan and Superior were much lower than that in the neighboring lake, Lake Erie, where the concentrations ranged from 24.2 to 107.1 nM in the surface (Townsend‐Small et al, ). This stark difference in concentrations is likely associated with active natural gas seeps, leaking natural gas pipelines, and the relatively shallow water column in Lake Eire (Townsend‐Small et al, ).…”

“…Concentrations in Lakes Michigan and Superior were much lower than that in the neighboring lake, Lake Erie, where the concentrations ranged from 24.2 to 107.1 nM in the surface (Townsend‐Small et al, ). This stark difference in concentrations is likely associated with active natural gas seeps, leaking natural gas pipelines, and the relatively shallow water column in Lake Eire (Townsend‐Small et al, ). While no acoustic investigations were conducted to identify seep bubbles in Lakes Michigan and Superior (Sheikh et al, ), our natural 14 C‐CH 4 measurements do not suggest that fossil seep CH 4 is a significant source to either the deep or surface waters in these lakes.…”

Large increases in emissions of methane and nitrous oxide from eutrophication in Lake Erie

“…The greenhouse gases CH 4 and N 2 O are 25 and 289 times more powerful than carbon dioxide (CO 2 ) over 100 year time scales, respectively (16). Despite decades of research on nutrients and phytoplankton in the Great Lakes, there is sparse research on GHGs in Lake Erie (17)(18)(19)(20)(21). However, if increasing eutrophication in Lake Erie linked to climate change leads to increasing emissions of CH 4 and N 2 O, this represents a positive feedback that urgently needs to be both delineated and addressed (22).…”

“…The main water source into Lake Erie is the upper Great Lakes via the Detroit River (24). Although drilling for oil and gas in the Great Lakes is currently banned in the United States, the Canadian waters of Lake Erie have been actively drilled for natural gas by Canada since the 1930s (18). Currently, there are over 2000 conventional natural gas wells offshore in the Canadian waters of Lake Erie (http://www.ogsrlibrary.com), approximately 500 of which are actively producing.…”