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PI-Submitted Research Highlights for
Terrestrial Ecosystem Science Program

Temporal and Spatial Variation in Peatland Carbon Cycling and Implications for Interpreting Responses of an Ecosystem-Scale Warming Experiment

Natalie A. Griffiths

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18 January 2018

Variability in peatland carbon cycle processes and implications for interpreting warming experiments.

The Science 
Scientists from Oak Ridge National Laboratory (ORNL) examined variability in peatland carbon stocks and fluxes measured over space and time using field measurements and modeling approaches.

The Impact
Peatlands are carbon-rich ecosystems, and, while it is common to measure peatland carbon stocks and fluxes, very few studies quantify variability in these measurements over space and time. This variability should be taken into account when interpreting the significance of experimental treatments, such as the warming and elevated carbon dioxide (CO2) treatments in the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment.

Summary
A team lead by ORNL are conducting a large-scale, long-term climate change response experiment in an ombrotrophic peat bog in Minnesota to evaluate the effects of warming and elevated CO2 on ecosystem processes, using empirical and modeling approaches. To better frame future assessments of peatland responses to climate change, the team characterized and compared spatial versus temporal variation in measured carbon cycle processes and their environmental drivers. They have also conducted a sensitivity analysis of a peatland carbon model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in carbon cycle processes resulted in the inability to determine if the bog was a carbon source or sink, as the 95% confidence interval ranged from a source of 50 grams of carbon per m2 per year (g C m2 yr–1) to a sink of 67 g C m2 yr–1. Model sensitivity analysis also identified that spatial variation in tree and shrub photosynthesis, allocation characteristics, and maintenance respiration all contributed to large variations in the pretreatment estimates of net carbon balance. Variation in ecosystem processes can be more thoroughly characterized if more measurements are collected for parameters that are highly variable over space and time, and especially if those measurements encompass environmental gradients that may be driving the spatial and temporal variation (e.g., hummock versus hollow microtopographies and wet versus dry years). Together, the coupled modeling and empirical approaches indicate that variability in carbon cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.

Contacts
BER Program Manager
Daniel Stover
Terrestrial Ecosystem Science, SC-23.1
Daniel.Stover@science.doe.gov (301-903-0289)

Principal Investigator
Natalie A. Griffiths
Oak Ridge National Laboratory
Oak Ridge, TN 37831
griffithsna@ornl.gov (865-576-3457)

Funding
This material is based on work supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy (DOE) Office of Science. Oak Ridge National Laboratory (ORNL) is managed by UT Battelle, LLC, for DOE under contract DEAC05-00OR22725. The Spruce and Peatland Responses Under Changing Environments (SPRUCE) experiment is a collaborative research effort between ORNL and the U.S. Department of Agriculture (USDA) Forest Service. The participation of Spatial Data Services (SDS) in SPRUCE efforts was funded by the Northern Research Station of the USDA Forest Service. A portion of this work was performed under the auspices of DOE by Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA27344.

Publications
Griffiths, N.A., P.J. Hanson, D.M. Ricciuto, C.M. Iversen, et al. “Temporal and spatial variation in peatland carbon cycling and implications for interpreting responses of an ecosystem-scale warming experiment.” Soil Science Society of America Journal 81(6), 1668–1688 (2017). [DOI:10.2136/sssaj2016.12.0422]

Related Links
Spruce and Peatland Responses Under Changing Environments project: https://mnspruce.ornl.gov/

ORNL TES SFA.
Funding: US Department of Energy, Office of Science, Office of Biological and Environmental Research.

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