Characterized by vast amounts of carbon stored in permafrost and a rapidly evolving landscape, the Arctic is an important focal point for the study of climate change. These are sensitive systems, yet the mechanisms responsible for those sensitivities remain poorly understood and inadequately represented in Earth System Models. The NGEE Arctic project seeks to reduce uncertainty in climate prediction by better understanding critical land-atmosphere feedbacks in terrestrial ecosystems of Alaska.
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.