Differences in Sediment Organic Matter Composition and PAH Weathering between Non-Vegetated and Recently Vegetated Fuel Oiled Sediments

Abstract

We examined polycyclic aromatic hydrocarbon (PAH) attenuation in contaminated field sediments after only 2 years of plant growth. We collected sediments from vegetated and non-vegetated areas at the Indiana Harbor Canal (IHC), an industrialized area with historic petroleum contamination of soils and sediments. PAH concentrations, PAH weathering indices, and organic matter composition in sediments colonized by Phragmites, cattails, or willow trees were compared to the same indices for non-vegetated sediments. We hypothesized that bulk sediment and humin fractions with measurable increases in plant organic matter content would show measurable changes to PAH attenuation as indicated by more weathered PAH diagnostic ratios or reduced PAH concentrations. Carbon-normalized PAH concentrations were lower in vegetated bulk sediments but higher in vegetated humin fractions relative to non-vegetated sediment fractions. Total organic carbon content was not indicative of more weathered N3/P2 ratios or reduced PAH concentrations in vegetated sediment fractions. More weathered N3/P2 ratios were observed with increased modern carbon (plant carbon) content of vegetated sediment fractions. Phragmites sediments contained more modern carbon (plant carbon) and more weathered PAH ratios [C3-naphthalenes and C2-phenanthrenes (N3/P2)] than willow, cattail, and non-vegetated sediments.

Differences in Pah Desorption and Sediment Organic Matter Composition Between Non-Vegetated and Recently Vegetated Fuel-Oiled Sediments

“…The same sediments used for this desorption study were also characterized by Gregory et al (2008). We previously reported total PAH concentrations of 42 alkylated and nonalkylated PAHs for the same IHC sediment fractions (Gregory and Nichols, 2008). Overall, Phragmites bulk sediment fractions had lower mean concentrations of TPAH than nonvegetated bulk sediments; whereas, total PAH concentrations in humin fractions were similar.…”

“…We were surprised to observe significant increases of plant carbon in vegetated IHC sediment and humin after only two years of Phragmites growth. In contrast, total organic carbon (% OC) did not change or was actually lower in Phragmites sediments than non-vegetated sediments (Gregory et al, 2008;see Table 2). Increased plant carbon content with negative or similar organic carbon content suggests increased biogenic carbon turnover, or humification, in vegetated sediment fractions.…”

“…The same sediments used for this desorption study were also characterized by Gregory et al (2008). We previously reported total PAH concentrations of 42 alkylated and nonalkylated PAHs for the same IHC sediment fractions (Gregory and Nichols, 2008).…”

“…Overall, Phragmites bulk sediment fractions had lower mean concentrations of TPAH than nonvegetated bulk sediments; whereas, total PAH concentrations in humin fractions were similar. We also previously reported differences in the organic matter composition (modern carbon and percent organic carbon) between vegetated and non-vegetated IHC sediments in Gregory et al 2008 and have provided those data in Table 2 as they are relevant to interpretation of PAH desorption behavior. Phragmites IHC sediment contained more modern carbon, or plant-derived carbon, than non-vegetated IHC sediment fractions.…”

“…The original composite sediments samples are referred to as bulk sediment fractions. Aliquots of bulk sediments (10-15 g) were freeze-dried then chemically fractionated to obtain de-ashed humin fractions according to previously described methods in Gregory et al, (2005Gregory et al, ( , 2008. Briefly, sediments were lipid-extracted twice then extracted with sodium hydroxide under a nitrogen headspace to remove humic and fulvic acids.…”