Influence of Land Slumping from Permafrost Thaw on Lake Methane Emissions in the Yukon-Kuskokwim Delta, Alaska
Abstract
Rising temperatures and increasing fire frequency across the Arctic are accelerating permafrost thaw, which can lead to substantial ground slumping in areas of high ice content. When these processes occur near lakeshores, deposition of recently-thawed organic matter into anoxic lake sediments has large potential to increase methane emissions. Specifically, this erosion may fuel methane release in the form of ebullition (bubbling from bottom sediments). High spatial and temporal variability in ebullition rates has made this type of gas emission difficult to quantify, and therefore it is often challenging to incorporate into Earth System Models. Ebullitive fluxes can be substantial, in some cases contributing the majority of methane emissions from lakes, as compared to diffusive fluxes. By studying ebullition in conjunction with ground slumping, we can better understand the factors influencing this source of CH4 emissions.
We measured both lake ebullitive and diffusive methane emissions in the Yukon-Kuskokwim Delta, AK, comparing rates between control sites that lacked ground slumping to sites with adjacent ground slumping. Diffusive fluxes were measured using a Los Gatos gas analyzer connected to a floating chamber. Bubble traps deployed above the sediment allowed us to measure sediment ebullition rates. Both were measured over a two week period in July 2019. We also collected gas bubbles to estimate methane concentrations in the gas being released. In order to determine the factors driving ebullition rates, intact sediment cores were collected, returned to the laboratory, and incubated anaerobically to estimate methane production. Sediments were also analyzed for C:N and composition of dissolved organic matter was analyzed using FTIR. Our findings show that ebullition rates were higher where ground slumping was high, yet diffusive CH4 flux was comparable in control and slumped areas. Methane production from sediment incubations was higher in the slumped areas and production rates were positively correlated with ebullition rates. Overall, our data suggest that ebullition is the major pathway of CH4 emissions from this lake. In addition, our findings may illustrate a positive climate feedback between permafrost thaw, erosion and lake methane emissions.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.B23K2450H
- Keywords:
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- 0426 Biosphere/atmosphere interactions;
- BIOGEOSCIENCES;
- 0428 Carbon cycling;
- BIOGEOSCIENCES;
- 0439 Ecosystems;
- structure and dynamics;
- BIOGEOSCIENCES;
- 0475 Permafrost;
- cryosphere;
- and high-latitude processes;
- BIOGEOSCIENCES