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Titel |
The assessment of point-source and diffuse soil metal pollution in Swansea (Wales, UK) using robust geostatistical methods. |
VerfasserIn |
B. P. Marchant, A. M. Tye, B. G. Rawlins |
Konferenz |
EGU General Assembly 2009
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 11 (2009) |
Datensatznummer |
250022707
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Zusammenfassung |
The urban area of Swansea was a centre of metal processing and production from the 16th
until the 20th century and was subject to a substantial amount of diffuse atmospheric
and point-source metal pollution. We map the concentrations of four heavy metals
across the urban region based upon a soil geochemical survey undertaken by the
British Geological Survey in the summer of 1994 covering an area of 93 km2 at a
density of 4 samples per km2. The non-aligned sampling grid yielded a total of 373
samples.
Analyses of these samples by X-ray fluorescence spectromety revealed that throughout
the urban area the concentrations of As, Cu, Pb and Sn were greater than the ambient
background concentrations. Several hotspots of each of these heavy metals were observed at
former industrial sites. These hotspots hinder the mapping of these metal concentrations by
conventional geostatistical methods in two ways. Firstly when models of spatial variation are
fitted to the data the hotspots lead to the variance of the metal concentrations being
over-estimated. This can in turn lead to details within our maps being smoothed out.
Secondly conventional interpolation techniques such as kriging exaggerate the size of the
hotspots.
Therefore the components of metal concentrations due to point-source and diffuse
pollution were mapped separately by robust geostatistical methods. We assume that the
dominant pattern of spatial variation of metal concentrations across the urban region results
from diffuse pollution whereas the hotspots are statistical outliers. Robust models of spatial
variation were used to represent the diffuse component of pollution. The parameters of these
models are not unduly influenced by the outliers. The diffuse pollution was mapped by robust
median kriging. This method is able to identify and truncate the outliers. Statistical
validation confirmed the appropriateness of the model of the spatial variation of metal
concentrations due to diffuse pollution. Historical records of industrial activity were used
to determine potential sources of contamination at the sites where outliers were
identified. |
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