Abstract
Human society has influenced the environment for at least thelast 15000 years but, since the Industrial Revolution, the
resultant environmental impacts have become more widespread.
Lake and reservoir bottom-sediments have been widely used in
many studies for reconstructing this impact over medium
timescales (tens to hundreds of years). Few long-term studies
of hydrological change exist and sediments are useful as
surrogates for direct monitoring since they are sensitive to
change within the catchment. This study uses the properties of
urban lake sediments in order to reconstruct environmental
pollution history.
The two principal objectives of this study were the
reconstruction of historical atmospheric, point source and
diffuse heavy metal pollution in an urban environment and the
evaluation of the lake-sediment record as a source of proxy
hydrological data over the last 100-150 years.
A paired lake-catchment study was undertaken by comparing
the records contained in a closed and an open lake. The closed
lake (Swanswell Pool) is situated in the centre of the city of
Coventry where the main source of pollution is atmospheric.
This site provides a contrast to an open basin (Wyken Pool)
with a multi- source catchment in addition to an atmospheric
influx.
Trends in urban lake sediment cores indicate increasing
heavy metal concentrations upcore, with cultural enrichment
factors for individual heavy metals of between 55.4 and 2.6.
Storage of heavy metals in the catchment of the closed basin
were significant, although it was found that up to 85% of the
zn and 90% of the Pb were actually stored in the lake
sediments. Catchment sources contributed up to 5 times more
than the atmosphere in the Wyken Slough catchment. Heavy
metals budgets were calculated, and these showed that loadings
of metals have increased by up to 7.5 times between 1850 and
the present day. Sequential digestion of the lake sediments at
both sites showed that the important fractions containing
heavy metals were Fe and Mn oxides and organic matter. The
heavy metals associated with these fractions could be
remobilised with changing environmental conditions, but an
analysis of contemporary water quality indicated that, at
present, suitable Eh and pH conditions for remobilisation did
not occur.
It was concluded that these urban lakes do preserve the
heavy metals record and can provide surrogate data on medium
term environmental change. However, the complex mixture of
materials associated with urban sedimentation resulted in a
lack of correlation between heavy metals and mineral magnetic
properties in either lake, and in the catchment of Wyken
Slough. Hence mineral magnetic properties of sediments in
urban catchments do not appear to be a suitable surrogate for
heavy metals analysis.
Urban lakes appear to provide a much-neglected opportunity
for palaeolimnological reconstruction over a period when
little directly monitored data exists.
| Date of Award | 1994 |
|---|---|
| Original language | English |
| Awarding Institution |
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