Dynamics of PAH deposition, cycling and storage in a mixed-deciduous (Quercus-Fraxinus) woodland ecosystem

Estimates of standing biomass and fluxes of biomass in a mixed-deciduous wo odland were derived, and used with results for concentrations of seven poly cyclic aromatic hydrocarbons (PAHs) in different compartments of the woodla nd system to quantitatively assess some of the key fluxes and burdens of PA Hs in this complex system. We quantified PAH burdens in air, in leaves of t hree deciduous tree species, in leaf litter and in soil, and uptake of PAHs by the tree leaves; PAH fluxes in litterfall, and deposition to the litter layer on the woodland floor during winter were calculated from these data. Air burdens exhibited marked seasonal variations for all compounds, with l owest values in summer when combustion-related emissions were low. Leaves d id not accumulate large burdens of PAHs while on the trees and consequently , litterfall-associated fluxes of PAHs were small, representing only a frac tion of the burdens in the litter layer to which they were deposited. Highe r PAH burdens in air in winter, combined with the organic-matter-rich natur e of the litter layer, are thought to be responsible for fluxes of PAHs to the litter layer in winter being 20-170 times the peak litterfall fluxes. T he soil compartment was calculated to contain 25 years' worth of deposition of benzo[ghi]perylene, the most recalcitrant PAH in this study. Storage qu otients for fluoranthene, pyrene, benzo[k]fluoranthene and benzo[a]pyrene b urdens in soil represented 7-10 years' worth of deposition, while fluorene and phenanthrene storage in soil approached unity with inputs (1 and 3 year s' worth of deposition, respectively). The relative importance of storage a nd loss processes was therefore closely related to the physico-chemical pro perties of the PAH, and is discussed in relation to the cycling of carbon i n the woodland. (C) 2001 Elsevier Science Ltd. All rights reserved.