Article pubs.acs.org/est
Field Measurements and Modeling of Ebullition-Facilitated Flux of Heavy Metals and Polycyclic Aromatic Hydrocarbons from Sediments to the Water Column Priscilla Z. Viana, Ke Yin, and Karl J. Rockne* S Supporting Information *
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−2 d−1, mean 140 ± 90 mmol m−2 d−1) and was highly temperature dependent. Ebullition-facilitated metal fluxes were large: 50 ± 13 mg m−2 d−1 (Fe), 2.6 ± 0.71 mg m−2 d−1 (Zn), 1.5 ± 0.28 mg m−2 d−1 (Pb), and 0.19 ± 0.06 mg m−2 d−1 (Cr). Ebullition-facilitated PAH fluxes were also large: 0.61 ± 0.27 mg m−2 d−1 for anthracene, 0.65 ± 0.28 mg m−2 d−1 for benzo[a]pyrene, 0.72 ± 0.28 mg m−2 d−1 for chrysene, 3.51 ± 1.23 mg m−2 d−1 for fluoranthene, 0.23 ± 0.08 mg m−2 d−1 for naphthalene, 3.84 ± 1.47 mg m−2 d−1 for phenanthrene, and 2.46 ± 0.86 mg m−2 d−1 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.
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water column,9,10 gas bubble migration may cause cap damage and a pathway for contaminant release.1,4 Widely varying gas production fluxes have been reported in the field. Tanner et al.11 observed methane fluxes varying from 0.07 to 0.67 L m−2 d−1 for wetlands used to treat wastewater. Sovik et al.12 measured gas production in 10 constructed wetlands, with fluxes of methane and carbon dioxide up to 53 and 47 L m−2 d−1, respectively. Ostrovski et al.13 reported a flux of 0.23 L m−2 d−1 from hypolimnetic sediments, and Wiesner et al.14 observed gas production fluxes of 2.7 L m−2 d−1 in a laboratory study with sediment from the Anacostia River, Washington, DC. A more complex mechanistic model that distinguishes between gas ebullition transport modes (fracturing versus pore perfusion) has recently been proposed for deep water sediments to predict the formation of gas hydrates.15 This model includes extremely fine-grained sediments (
