Heavy metal concentrations in sediment deposits on the Tar River floodplain following Hurricane Floyd |
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Authors: | Patrick Pease Scott Lecce Paul Gares Catherine Rigsby |
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Institution: | (1) Department of Geography, University of Northern Iowa, Cedar Falls, IA 50614-0406, USA;(2) Department of Geography, East Carolina University, Greenville, NC 27858-4353, USA;(3) Department of Geology, East Carolina University, Greenville, NC 27858-4353, USA |
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Abstract: | The relation between the magnitude of a flood event and the resulting environmental impacts remains unclear. This study examines
the impact of the flood of record on heavy metal deposition on the Tar River floodplain in eastern North Carolina, USA. Samples
of sediment deposited on the floodplain following Hurricane Floyd were collected from 85 sites along the lower Tar River basin
and analyzed for heavy metal concentration. The Hurricane Floyd event is the flood of record for the Tar River basin. Despite
the magnitude of the flood, little suspended sediment was deposited on the floodplain. In almost all cases the deposition
was less than 0.2 cm. There was variability in heavy metal content from site to site, but the overall concentrations were
lower than might be expected for a flood of the magnitude of Floyd. To aid in comparison of contamination levels, the heavy
metal concentrations were normalized to two environmental standards; the EPA preliminary remediation goals for residential
soil and the general background concentrations of stream sediments throughout the Tar River basin. Most samples were highly
enriched in heavy metals relative to the background concentration of stream sediments. However, samples were generally not
contaminated relative to EPA PRG regulations. Arsenic, which was significantly elevated in nearly all samples, was the only
exception. This contradiction makes it clear that the standard to which contaminants are compared must be considered carefully.
The overall low concentration of heavy metals was likely the result of smaller flooding from Hurricane Dennis, 10 days prior
to Hurricane Floyd, moving most of the stored sediment out of the basin prior to wide-spread overtopping of the banks. The
implication is that event sequencing is as important as flood magnitude when examining environmental impacts. |
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Keywords: | Flood Heavy metals Floodplain |
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