Local Heterogeneity of Carbon Accumulation Throughout the Peat Profile of an Ombrotrophic Northern Minnesota Bog

Past carbon accumulation in peat of the SPRUCE bog helps understand response to experimental treatments.

The Science

Scientists from Oak Ridge National Laboratory (ORNL) and Lawrence Livermore National Laboratory (LLNL) measured carbon storage and age of 18 peat depth profiles at the Spruce and Peatland Responses Under Changing Environments (SPRUCE) experimental site, constructed peat age-depth models, and quantified rates of carbon accumulation over the history of the bog to assess potential sources for variation in accumulation of carbon over time and space. Calibrated peat ages and age-depth profiles are available for use by SPRUCE collaborators and the broader community.

The Impact

This study found that the bog has been accumulating carbon in peat for over 11,000 years. Carbon accumulation rates changed over time, with a period of low net carbon accumulation likely a result of warmer and drier environmental conditions between 100 and 3300 years before present. These results suggest that experimental warming treatments, as well as a future warmer climate, may reduce net carbon accumulation in peat in this and other southern boreal peatlands.

Summary

ORNL and LLNL scientists evaluated the spatial heterogeneity of historical carbon accumulation rates in a forested, ombrotrophic bog in Minnesota to aid understanding of responses to an ongoing decade-long warming manipulation (SPRUCE). Eighteen peat cores indicated that the bog has been accumulating carbon for over 11,000 years, to yield an average of 176 kg C per m2 to 225 cm of peat depth. The long-term apparent rate of carbon accumulation over the entire peat profile averaged 22 kg C m2 yr–1. Net carbon accumulation rates averaged 30 ± 2 g C m2 yr–1 prior to 3300 cal BP, when net carbon accumulation rates dropped to 15 ± 8 g C m2 yr–1. Net carbon accumulation rates increased again during the last century to 74 ± 57 g C m2 yr–1. During the period of low accumulation, regional droughts may have lowered the water table, allowing for enhanced aerobic decomposition and making the bog more susceptible to fire. These results suggest that experimental warming treatments, as well as a future warmer climate, may reduce net carbon accumulation in peat in this and other southern boreal peatlands.

Principal Investigator

Karis McFarlane
Lawrence Livermore National Laboratory
kjmcfarlane@llnl.gov

Program Manager

Daniel Stover
U.S. Department of Energy, Biological and Environmental Research (SC-33)
Environmental System Science
daniel.stover@science.doe.gov

Funding

This work was supported by the Office of Biological and Environmental Research, within the U.S. Department of Energy Office of Science, under project ERKP788 and SWC1447; and Lawrence Livermore National Laboratory, Laboratory Research and Development project 14-ERD-038.

References

McFarlane K. J., P. J. Hanson, C. M. Iversen, and J. R. Phillips, et al. "Local spatial heterogeneity of Holocene carbon accumulation throughout the peat profile of an ombrotrophic Northern Minnesota bog". Radiocarbon 60 (3), 941–962  (2018). http://dx.doi.org/10.1017/RDC.2018.37.