HR: 1340h
AN: B33E-1094    [Abstracts]
TI: Black (Pyrogenic) Carbon as a Component of Carbon Cycling and Ecosystem Function in Boreal Regions
AU: * Preston, C M
EM: cpreston@pfc.cfs.nrcan.gc.ca
AF: Caroline M. Preston, Pacific Forestry Centre 506 W. Burnside Rd., Victoria, BC V8Z 1M5 Canada
AU: Schmidt, M W
EM:
AF: Michael W. I. Schmidt, Dept. of Geography University of Zurich Winterthurerstr. 190, Zurich, 8057 Switzerland
AB: The carbon (C) cycle in boreal regions is strongly influenced by fire, which converts a small fraction (1-7% of mass) to pyrogenic C (PyC). PyC is mainly produced as solid charred residues including a black carbon (BC) fraction chemically defined by its oxidation resistance, plus much lower proportions of volatile soot and polycyclic aromatic hydrocarbons (PAHs). All PyC is characterized by fused aromatic rings, but varying in cluster sizes and degree of ordering, and presence of other elements (N, O) and functional groups. Char PyC is expected to be highly resistant to decomposition, and therefore to contribute to very stable C pools in soils and sediments. It also appears to influence soil processes, mainly through its sorption properties and contribution to cation exchange capacity. By contrast, soot aerosols absorb solar radiation, and may contribute to global warming. However, information is lacking to integrate PyC into C cycle and atmospheric models for boreal regions. Analytical methods are still under development and individual methods, which are mainly based on various measures of oxidation resistance, capture different fractions of the PyC ``continuum''. Short- term incubations indicate a small initial breakdown of solid PyC, leveling off after 1-2 years. Quantitative long-term field studies on PyC longevity are missing, but circumstantial evidence suggests turnover on a millennium timescale (5,000-10,000 y), depending on environmental conditions and PyC properties. Degraded, functionalized PyC becomes water soluble and has been detected in river water and sediments. We have synthesized the limited information available on production, stocks, characteristics, and loss processes of PyC in boreal forests (data on peatlands are almost non- existent). Annual production is estimated as 8 Tg PyC, including perhaps 2.4 Tg C of the more resistant BC fraction. The main limitation to the sink potential of PyC is likely its consumption by subsequent fires, but there are substantial gaps in our knowledge of its role in boreal C cycling.
DE: 4806 Carbon cycling (0428)
SC: Biogeosciences [B]
MN: Fall Meeting 2005