Variability in peatland carbon cycle processes and implications for interpreting warming experiments.
Scientists from Oak Ridge National Laboratory examined variability in peatland carbon stocks and fluxes measured over space and time using field measurements and modeling approaches.
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 CO2 treatments in the SPRUCE experiment.
A team lead by ORNL is 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 vs. temporal variation in measured C cycle processes and their environmental drivers. They have also conducted a sensitivity analysis of a peatland C model to identify how variation in ecosystem parameters contributes to model prediction uncertainty. High spatial variability in C cycle processes resulted in the inability to determine if the bog was a C source or sink, as the 95% confidence interval ranged from a source of 50 g C m-2 yr-1 to a sink of 67 g C m-2 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 C 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 vs. hollow microtopographies, and wet vs. dry years). Together, the coupled modeling and empirical approaches indicate that variability in C cycle processes and their drivers must be taken into account when interpreting the significance of experimental warming and elevated CO2 treatments.
Contacts (BER PM)
Natalie A. Griffiths
Oak Ridge National Laboratory
This material is based on work supported by the US Department of Energy, Office of Science, Office of Biological and Environmental Research. Oak Ridge National Laboratory (ORNL) is managed by UT Battelle, LLC, for the US Department of Energy under contract DEAC05-00OR22725. The SPRUCE experiment is a collaborative research effort between ORNL and the USDA Forest Service. The participation of 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 the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
Griffiths, N.A., P.J. Hanson, D.M. Ricciuto, C.M. Iversen, A.M. Jensen, A. Malhotra, K.J. McFarlane, R.J. Norby, K. Sargsyan, S.D. Sebestyen, X. Shi, A.P. Walker, E.J. Ward, J.M. Warren, and D.J. Weston. “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, 1668-1688 (2017). [DOI:10.2136/sssaj2016.12.0422]
Spruce and Peatland Responses Under Changing Environments project: https://mnspruce.ornl.gov/
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