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Fate and Transport of Carbon in Northern Soils: Merritt R. Turetsky
Project Title: Fate and Transport of Carbon in Northern Soils
Mendenhall Fellow: Merritt R. Turetsky, (650)-329-5005, mturetsky@usgs.gov
Duty Station: Menlo Park, CA
Start Date: November 1, 2002
Education: Ph.D. (Biological Sciences), University of Alberta, 2002
Research Advisors: Jennifer Harden, (650) 329-4949, jharden@usgs.gov; Jason Neff, (303) 492-6187, Jason.C.Neff@colorado.edu; A. David Maguire, (907) 474-6242, ffadm@uaf.edu

Project Description: Boreal forests represent about 10% of the Earth's land area but store up to 40% of the world’s terrestrial carbon (C). The majority of this soil C is found in deep deposits of organic debris or peat, which have accumulated slowly since the last glacial retreat. Peat accumulates when CO2 fixation through plant production exceeds C releases primarily through decomposition. Fire also is an important control on terrestrial carbon stocks, as burning releases C to the atmosphere through combustion of organic matter, alters patterns of plant and microbial activity, and increases the export of dissolved and particulate C. Over the past several decades, fire frequencies have increased in many boreal regions due to a combination of climate change and increased anthropogenic activity. Generally, global warming is predicted to be most pronounced at high latitudes. Thus, an understanding of how C sequestration in boreal and subarctic soils is controlled both by climate and disturbance is important for predicting the future response of C stocks to CO2-induced warming.

Research Objectives:

  1. Reconstructing losses of terrestrial C to combustion during wildland burning: Increased fire frequencies likely will lead to decreasing C storage in boreal ecosystems. The combustion of organic matter during burning represents a major loss of terrestrial C to the atmosphere, yet current estimates of combustion during wildland fires are scarce and extremely variable. Soil drainage is thought to be an important control on fire activity, with lower fire frequency and severity in more poorly drained landscapes. However, despite the massive stocks of C stored in peatlands today, the relative susceptibility of peatlands to burning is not well understood. While charcoal records in peat commonly are used to establish fire frequencies and changes in C accumulation in response to fires, few studies have directly quantified C losses during organic matter combustion in peatlands. New methodology outlined by Turetsky and Wieder (2001) allows for direct estimation of C combustion losses based on differences in ash concentration between burned and unburned peat. In collaboration with Kristen Manies (USGS), Jennifer Harden (USGS), and Eric Kasischke (U. Maryland), this project utilizes these chemical differences to reconstruct C combustion rates across recently burned areas in Alaska and western Canada. In each fire event, sampling encompasses both well- and poorly- drained landscape positions. The goals of the work are (1) to test various approaches for reconstructing combustion rates during wildland and prescribed fires, (2) to provide data on the spatial heterogeneity of organic matter combustion during burning, and (3) to build statistical models investigating the controls of landscape position/soil drainage and seasonality on organic matter combustion. These data will be made available to the modeling community to help constrain values for combustion rates in ecosystem C models.
  2. Burning effects on substrate quality and decomposition: In addition to immediate losses of C to the atmosphere during organic matter combustion, fires can have long-term effects on both plant and microbial activity by altering nutrient regimes, soil climates, and organic matter quality. In collaboration with Kristen Manies (USGS), Jennifer Harden (USGS), Jason Neff (U. Colorado), and Michelle Mack (U. Florida), this project utilizes two approaches to address the interactions between burning, substrate quality, and decomposition. Reciprocal transplants of burned and unburned litter into replicate black spruce-feather moss forests in interior Alaska will separate the influence of environmental versus burning effects on organic matter quality and rates of decomposition (quantified as litterbag mass losses over time). Secondly, CO2 and DOC production are being quantified in burned and unburned soils during laboratory incubations under standardized temperature and moisture conditions. This work will provide additional insight into the controls of vegetation (feather moss- versus Sphagnum- derived soils) and burning (burned versus unburned) on rates of decomposition. In addition, temperature and soil moisture are being varied during these incubations to address soil climate controls on CO2 and DOC production in northern soils. Together, these complementary approaches will provide an understanding of how climate (temperature, moisture) and substrate quality (determined by vegetation, burning, etc.) interact to control rates of decomposition in boreal ecosystems.

Reference Cited:
Turetsky, M.R. and R.K. Wieder. 2001. A direct, field approach to quantifying organic matter lost as a result of peatland wildfire: Canadian Journal of Forest Research, v.31. p. 363-366.

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