Field Measurements and
Modeling of Ebullition-Facilitated
Flux of Heavy Metals and Polycyclic Aromatic Hydrocarbons from Sediments
to the Water Column
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Abstract
Gas ebullition-facilitated transport of metals and polycyclic
aromatic
hydrocarbons (PAHs) from sediment was investigated in 14 urban waterway
locations. Gas ebullition varied widely over four seasons (range 2–450
mmol m<sup>–2</sup> d<sup>–1</sup>, mean 140 ±
90 mmol m<sup>–2</sup> d<sup>–1</sup>) and was highly
temperature dependent. Ebullition-facilitated metal fluxes were large:
50 ± 13 mg m<sup>–2</sup> d<sup>–1</sup> (Fe),
2.6 ± 0.71 mg m<sup>–2</sup> d<sup>–1</sup> (Zn),
1.5 ± 0.28 mg m<sup>–2</sup> d<sup>–1</sup> (Pb),
and 0.19 ± 0.06 mg m<sup>–2</sup> d<sup>–1</sup> (Cr). Ebullition-facilitated PAH fluxes were also large: 0.61 ±
0.27 mg m<sup>–2</sup> d<sup>–1</sup> for anthracene,
0.65 ± 0.28 mg m<sup>–2</sup> d<sup>–1</sup> for
benzo[a]pyrene, 0.72 ± 0.28 mg m<sup>–2</sup> d<sup>–1</sup> for chrysene, 3.51 ± 1.23 mg m<sup>–2</sup> d<sup>–1</sup> for fluoranthene, 0.23 ± 0.08 mg m<sup>–2</sup> d<sup>–1</sup> for naphthalene, 3.84 ± 1.47 mg m<sup>–2</sup> d<sup>–1</sup> for phenanthrene, and 2.46 ± 0.86 mg
m<sup>–2</sup> d<sup>–1</sup> for pyrene. The magnitude
of these fluxes indicates that gas ebullition is an important pathway
for release of both PAHs and heavy metals from buried sediments. Multivariate
regression analysis of the in situ gas ebullition flux and ebullition-facilitated
contaminant flux suggests that metal transport likely is due to sediment
particle resuspension, whereas PAH transport is due to both contaminant
partitioning to gas bubbles and to sediment resuspension. These results
indicate that assumptions regarding the natural recovery potential
of ebullition-active sediments should be made with caution