ARTICLE pubs.acs.org/est
Comparative Floc-Bed Sediment Trace Element Partitioning Across Variably Contaminated Aquatic Ecosystems Amy V. C. Elliott,† Janina M. Plach,† Ian G. Droppo,‡,† and Lesley A. Warren*,† † ‡
School of Geography and Earth Sciences, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4K1, Canada National Water Research Institute, Environment Canada, P.O. Box 5050, Burlington, Ontario, L7N 4A6, Canada
bS Supporting Information ABSTRACT: Significantly higher concentrations of Ag, As, Cu, Ni and Co are found in floc compared to bed sediments across six variably impacted aquatic ecosystems. In contrast to the observed element and site-specific bed sediment trace element (TE) partitioning patterns, floc TE sequestration is consistently dominated by amorphous oxyhydroxides (FeOOH), which account for 30 79% of floc total TE concentrations, irrespective of system physico-chemistry or elements involved. FeOOH consistently occur in significantly higher concentrations in floc than within bed sediments. Further, comparative concentration factors indicate significantly higher TE reactivity of floc-FeOOH relative to sediment-FeOOH in all systems investigated, indicating that both the greater abundance and higher reactivity of floc-FeOOH contribute to enhanced floc TE uptake. Results indicate that floc-organics (live cells and exopolymeric substances, EPS) directly predict floc-FeOOH concentrations, suggesting an organic structural role in the collection/templating of FeOOH. This, in turn, facilitates the sequestration of TEs associated with floc-FeOOH formation, imparting the conserved FeOOH “signature” on floc TE geochemistry across sites. Results demonstrate that the organic rich nature of floc exerts an important control over TE geochemistry in aquatic environments, ultimately creating a distinct solid with differing controls over TE behavior than bed sediments in close proximity (2000 L) was pumped (6 L min 1) into CFC bowls with a rotational speed of 9470 rpm. Percent recovery of floc at each field site was >90% (assessed by weight comparison of CFC inflow and outflow filtered water samples on glass-fiber Whatman filters following the standard method 2540D 19). Surficial (0 1 cm) bed sediment samples were collected by extruding SCUBA-diver retrieved polycarbonate cores (6 cm diameter, 45 cm length) immediately after retrieval. All sediment samples were frozen on dry ice in the field and stored at 20 °C until analysis. Floc for imaging analyses were collected from diverretrieved plankton chambers. Trace Element Analyses. Aqueous trace element ([TE]D: dissolved,
