Urban runoff and flocculated sediment quality in the South Saskatchewan River
Date
2003-09
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ORCID
Type
Degree Level
Masters
Abstract
Urban runoff poses a threat to water quality. Some contaminants in urban runoff,
such as heavy metals, are preferentially bound to fine-grained sediment. Fine-grained
sediment in fluvial systems is transported as composite particles known as "floes".
Floes are deposited as a thin layer of surficial fine-grained laminae (SFGL) during
periods of low flow velocity and shear stress. SFGL deposits have been identified as a
possible in-channel sink and source of fine-grained sediment and associated
contaminants that may be useful in determining anthropogenic impacts on rivers. The
objective of this study was to examine changes in the physical and chemical
characteristics of SFGL in response to urban runoff, and to assess the applicability of
SFGL to water and sediment quality studies.
SFGL samples were collected from the South Saskatchewan River, upstream and
downstream of the city of Saskatoon, before, during and after rainstorms. The sediment
was analyzed for trace element composition, organic carbon content and particle size
distribution to characterize the physical and chemical nature of SFGL. Fine-grained
storm water outflow sediment was also collected to characterize urban runoff inputs to
the river.
The physical characteristics of SFGL varied with season and suspended sediment
concentration. Variations in the trace element chemistry of SFGL were due to changes
in the physical composition of sediment in terms of % silt and clay and the chemical
characteristics of the sediment in terms of % TOC (total organic carbon), and were not
directly attributed to changing hydrologic conditions such as discharge, rainfall and
runoff. As, Cr, Cu and Ni concentrations in SFGL exceeded sediment quality
guidelines. The downstream decrease in trace element concentrations of SFGL may be
attributed to dilution by uncontaminated sediment, or the presence of a sediment sink
upstream of the downstream sampling site. Fine-grained sediment carried by urban
runoff and discharged to the river at storm water outflows was a source for Cu, Zn, Pb
and Sn. Nevertheless, there may not have been a sufficient quantity of this contaminantenriched
sediment to have an impact on sediment-associated trace element
concentrations downstream of the city.
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Degree
Master of Science (M.Sc.)
Department
Geography
Program
Geography