DIfferences in Sediment Organic Matter Composition and PAH Weathering Between Non-Vegetated and Recently Vegetated Fuel-Oiled Sediments

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Title: DIfferences in Sediment Organic Matter Composition and PAH Weathering Between Non-Vegetated and Recently Vegetated Fuel-Oiled Sediments
Author: Gregory, Samuel Thorne III
Advisors: Elizabeth Nichols, Committee Co-Chair
Damian Shea, Committee Co-Chair
Chris Hofelt, Committee Member
Abstract: Previous results have shown a strong correlation between vegetation and dissipation of polycyclic aromatic hydrocarbon (PAH) contamination over long time frames. Evidence of phytoremediation over shorter time frames is difficult to detect, particularly in sites where overall PAH concentrations have not begun to significantly decrease. This study assessed the impact of vegetation on a highly contaminated sediment over a short time frame in order to track the effects of plant derived organic carbon (PdOC) in a variety of sediment compartments. The Indiana Harbor Canal is an industrialized area with historic petroleum contamination of near-shore sediments. In 2002, near-shore sediments were planted with hybrid poplar and willow trees as part of a phytoremediation treatability study. Site disturbance allowed for colonization by cattails and Phragmites. In 2004, non-vegetated and vegetated oiled-shore sediments were collected and analyzed for 42 polycyclic aromatic hydrocarbons (PAHs), total organic carbon, and percent modern carbon (14C radiocarbon). Sediments were collected from several locations, field-composited, homogenized, sieved, and chemically fractionated. There is a significant input of modern carbon in both labile and recalcitrant fractions of vegetated sediments that is absent in the non-vegetated control. Phragmites sediments contained more modern carbon (plant carbon) and more weathered PAH ratios than willow, cattail, and non-vegetated sediments. Organic carbon-normalized PAH concentrations were greater in Phragmites humin than other sediments. Humin fractions of willow trees were more weathered than non-vegetated humin, but modern carbon values were not always different. Cattail humin contained more modern carbon than non-vegetated humin, but only de-ashed humin was more weathered than non-vegetated de-ashed humin. Results show that sediment composition and PAH weathering indices are not indicative of reduced PAH concentrations. Instead, PAH weathering appears related to increased modern carbon (plant carbon) content. Substantial increases in modern carbon content were observed after two years of plant growth. These results suggest that PdOC is diffusing into a variety of sediment compartments where it may be enhancing carbon cycling and beginning to mitigate PAH concentrations.
Date: 2007-10-15
Degree: MS
Discipline: Toxicology
URI: http://www.lib.ncsu.edu/resolver/1840.16/2099

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