HR: 09:15h
AN: B21C-06    [Abstracts]
TI: Influence of Forest-type and Organic Matter Maturity on Pb-speciation and Mobility in Forest Soils of the Northeastern U.S.
AU: * Schroth, A W
EM: andrew.schroth@dartmouth.edu
AF: Dartmouth College Department of Earth Sciences, 6105 Fairchild Hall, Hanover, NH 03755 United States
AU: * Schroth, A W
EM: andrew.schroth@dartmouth.edu
AF: Dartmouth College Environmental Studies Program, 6182 Steele Hall, Hanover, NH 03755 United States
AU: Bostick, B C
EM: Ben.Bostick@Dartmouth.edu
AF: Dartmouth College Department of Earth Sciences, 6105 Fairchild Hall, Hanover, NH 03755 United States
AU: Kaste, J M
EM: Jim.Kaste@dartmouth.edu
AF: Dartmouth College Department of Earth Sciences, 6105 Fairchild Hall, Hanover, NH 03755 United States
AU: Kaste, J M
EM: Jim.Kaste@dartmouth.edu
AF: Dartmouth College Environmental Studies Program, 6182 Steele Hall, Hanover, NH 03755 United States
AU: Friedland, A J
EM: Andy.Friedland@Dartmouth.edu
AF: Dartmouth College Environmental Studies Program, 6182 Steele Hall, Hanover, NH 03755 United States
AB: Several studies have suggested that forest-type plays an important role in the deposition and mobility of atmospherically derived anthropogenic lead within forest soils, but a specific forest-type effect remains elusive because of confounding and complimentary variables associated lead mobility within natural systems. Here we examine the amount and speciation of lead in forest floor (O) and mineral (A) horizons collected from soils under different forest-types (northern hardwood, Norway spruce, red pine, white pine) at sites where variables that could influence lead deposition or migration aside from overstory species are controlled (elevation, aspect, soil type, parent material composition). We find significant (p<0.05) differences in lead amounts in forest floors and surface mineral soils, where conifer forests had more lead in forest floors, while surface mineral soils under northern hardwood forests had higher amounts of lead than comparative conifer soils. These differences in Pb concentration and distribution reflect the increased interception of aerosol-derived Pb by conifers, and the quality of litter produced by each species (hardwood>conifer) that influences the organic matter's susceptibility to microbial attack and associated decomposition. To examine on a mechanistic scale the influence of decomposition on Pb mobility, we conducted long-term litter decay experiments with lead additions and examined lead speciation through a decomposition continuum using synchrotron-based X-ray spectroscopy, micro X-ray diffraction, micro X-ray fluorescence, and selective extractions. This experiment allows us to understand the dynamic nature of lead speciation as humification progresses and assess its influence on lead mobility over time. Lead is initially bound primarily to the surface of organic material, but as these molecules breakdown during decomposition, increasing fractions of anthropogenic lead are bound to colloidal mineral phases, primarily amorphous iron oxides. Such insoluble mineral phases most likely play an important role in lead mobility in soils over time and may be responsible for observed variations in lead mobility by species. These results have important ramifications for assessing the threat of regional (leaded gasoline-based) and localized (i.e. smelter areas) lead pollution to terrestrial and aquatic systems.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0426 Biosphere/atmosphere interactions (0315)
DE: 0461 Metals
DE: 1023 Composition of the biosphere
DE: 1065 Major and trace element geochemistry
SC: Biogeosciences [B]
MN: Fall Meeting 2005