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Comparing near-shore and mid-lake eddy covariance measurements of methane and carbon dioxide fluxes
Citation:
Waldo, S., J. Beaulieu, W. Barnett, AND Johnt Walker. Comparing near-shore and mid-lake eddy covariance measurements of methane and carbon dioxide fluxes. Presented at Ameriflux PI Meeting 2018, Bloomington, Indiana, October 23 - 25, 2018.
Impact/Purpose:
The purpose of this poster is to share the EPA work monitoring reservoir-atmosphere gas exchange with other experts in my field, and to confer with them about best practices and data interpretation. These findings can help inform the scientific community that are involved in flux-tower monitoring (e.g. members of the Ameriflux network) of important considerations when siting a measurement tower. Reservoirs are a globally important source of methane (CH4) to the atmosphere, and can be net carbon dioxide (CO2) sources as well. Determining the CH4 and CO2 emission strength from reservoirs is made challenging by the spatial and temporal variation in fluxes. In particular, the patchy nature of the often dominant CH4 emission pathway, ebullition (bubbling), hampers upscaling. The relatively large footprint and continuous measurements of the eddy covariance (EC) method make it a useful way to characterize trace gas fluxes over reservoirs. However, siting EC instrumentation to measure reservoir fluxes can be logistically difficult. This poster presents EC flux results from two different tower sites at Acton Lake, a small eutrophic reservoir in southwestern Ohio. The first site was in use from January 2017 – March 2018 and was located on a dock ~20 m from shore on the NW side of the lake (“dock site”). In May of 2018 the EC system was moved 200 m from the E shore of the lake and mounted on an aluminum tower (“aquatic tower site”). In addition to reducing rejection of fluxes from non-target footprint periods, a goal of moving the EC system away from the shore was to address rotor effects from the landscape transition. The gains of moving the EC system to a more ideal site are assessed in this poster, including the benefits of increasing data coverage of the 30-minute fluxes from 25% to 65%. Spatial patterns in CO2 emission related to lake zone are also presented.
Description:
Reservoirs are a globally important source of methane (CH4) to the atmosphere, and can be net carbon dioxide (CO2) sources as well. Determining the CH4 and CO2 emission strength from reservoirs is made challenging by the spatial and temporal variation in fluxes. In particular, the patchy nature of the often dominant CH4 emission pathway, ebullition (bubbling), hampers upscaling. The relatively large footprint and continuous measurements of the eddy covariance (EC) method make it a useful way to characterize trace gas fluxes over reservoirs. However, siting EC instrumentation to measure reservoir fluxes can be logistically difficult. This poster presents EC flux results from two different tower sites at Acton Lake, a small eutrophic reservoir in southwestern Ohio. The first site was in use from January 2017 – March 2018 and was located on a dock ~20 m from shore on the NW side of the lake (“dock site”). In May of 2018 the EC system was moved 200 m from the E shore of the lake and mounted on an aluminum tower (“aquatic tower site”). In addition to reducing rejection of fluxes from non-target footprint periods, a goal of moving the EC system away from the shore was to address rotor effects from the landscape transition. The gains of moving the EC system to a more ideal site are assessed in this poster, including the benefits of increasing data coverage of the 30-minute fluxes from 25% to 65%. Spatial patterns in CO2 emission related to lake zone are also presented.