Monday, July 15, 2013

Chambers used to estimate CO2 and CH4 flux

One of the primary goals of the NGEE Arctic project is to characterize carbon cycle feedbacks between tundra ecosystems and climate. We have larger, more holistic goals as well, but this is a major component of our studies. Therefore, we have made a considerable effort to emphasize measurements of CO2 and CH4 flux to and from soils and vegetation. This includes deployment of an eddy covariance system on the Barrow Environmental Observatory (BEO) to characterize carbon fluxes at landscape scales. Dave, Naama, and Margaret are handling those aspects of the project. Dave is from the University of Nebraska and is one of our collaborators; Margaret and Naama are from LBNL. We also took soil cores in the field last spring that we are studying now in the laboratory under controlled conditions. David and Taniya at ORNL are conducting those studies. I look forward to seeing data from these large and small scale investigations.

In addition to our eddy covariance and permafrost core measurements of carbon fluxes, our NGEE Arctic team has also deployed several different manual and automated chambers in the field for estimating CO2 and CH4 fluxes. Evidence for these intermediate-scale approaches can be seen scattered about the tundra. Melanie has placed white PVC collars in our permanent plots and within the eddy covariance footprint. A chamber can be manually attached to these collars and measurements of CO2 and CH4 flux made throughout the summer.


Lydia and Bryan, both from LBNL, have deployed similar chambers in our various plots both along our transects and in our intensive plots that encompass low-, transitional-, and high-centered polygons. These chambers can be monitored for carbon fluxes, but they are also being used to collect gas samples for 14C analysis. This is done by connecting small evacuated cylinders to chambers sealed to the soil surface again via collars. Gas samples can then be analyzed for 14C and determinations made as to the age of carbon being emitted from thawing permafrost. These measurements will be critical in combination to some of our other process measurements as we better represent carbon cycle dynamics in models.

The chambers that Lydia and Bryan have deployed are convenient for measuring CO2 and CH4 fluxes across that landscape, but tend to be limited to weekly campaigns. It is difficult with those kind of chambers to get temporally-resolved estimates of flux at, for example, hourly intervals throughout the day. We overcome that limitation by using automated chambers. These require a source of power, but can collect information on soil respiration or ecosystem gas exchange, depending on the exact type of chamber, throughout the day, week, or season. Melanie from the University of California, Berkeley has deployed one of these chambers near our eddy covariance tower.

Together with our other measurements like soil temperature, moisture, redox, etc., these chambers should be helpful as we seek to improve representation of carbon cycle processes in climate models. Given enough data, we can more fully understand what controls rates of CO2 and CH4 flux for Arctic ecosystems. In order to do that, we must bring together supporting data from genomics, hydrology, biogeochemistry, vegetation dynamics, and subsurface science. We have a good team for tackling this objective.