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| Titel |
The role of salt marshes as heavy metal sinks in cantabrian seaboard (Bay of Biscay) |
| VerfasserIn |
Susana Fernandez, Manuel Antonio González, Cristina Santin, Miguel Ángel Álvarez |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250058062
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| Zusammenfassung |
| Estuarine sediments are at the same time important sinks and potential sources of heavy
metals. Under natural conditions the geochemical composition of the suspended fluvial
sediments, which arrive to the estuarine systems, mainly depend on the rock substrata
composition of the river basin.
Land reclamation in salt marshes has led to intense physical and chemical changes in
sediments and soils, triggering serious environmental problems. The development of acid
sulphate soils and toxicity caused by the release of trace elements are the main environmental
problems arise from the ripening of the reclaimed tidal lands.
In order to elucidate the capability of the estuarine sediments to accumulate and/or
release of heavy metals, two estuarine- river basin systems were analysed: Nalón
and Sella. The Nalón River has 815, 8 km of channels with fluvial sediments and
daily flow average of 56,4 m3/s. More than 3500 km2 of the river basin bedrock
are compound by siliceous rocks (metamorphic slates, quartzite sandstone and
sedimentary slate). At the mouth, develops a large estuarine system with more than
527 ha of extension. Many parts of this saltmarsh have been drained and used to
human developing purposes. The Sella River has 192,6 km of fluvial channel with
a daily flow discharge is about 42,8 m3/s. The development of fluvial sediments
is lesser than in Nalón River due to the overdeeping of the channels which cross
mainly calcareous bedrock with a very strong topography. This river develops in the
mouth an estuarine area with 271 ha of extension. This area suffers an important
urban and tourist human pressure which gave rise the reclamation of more than 200
ha.
A total amount of 102 soil fluvial samples spread over the 9 sub- watersheds of the Nalón
river basin were taken. In the estuary 3 samples in natural mud sediments and 3 in reclaimed
mud were taken. In Sella River basin 21 fluvial soil samples spread over 3 sub
watersheds and 6 samples more, 3 in estuarine mud and 3 in reclaimed one were
taken.
In each sample the concentration of Mn(ppm); Zn(ppm); Cr(ppm); Pb(ppm); Ba(ppm)
V(ppm) Co(ppm); Ni(ppm); Cu(ppm); Tl(ppb); Sn(ppm); As(ppm); Mo(ppm); Ag(ppb);
Cd(ppb); Sb(ppb); Hg(ppb) using a ICP-MS and other soil variables as pH; MO%; Clay%;
Silt%; Sand% and EC(mS/m3).
In order to compare fluvial, natural and reclaimed mud soils, average of metals
concentration in each sub watersheds were calculated. In Nalón basin one population of 9
fluvial soil values ( one per sub watershed) were compared to 3 samples of mud and 3
samples of reclamation mud. In Sella basin one population of 3 fluvial soil values (3
subwatershed) were compared to 3 mud and 3 reclaimed one.
The highest concentrations of some toxic heavy metals are found in the natural
estuarine sediments (e. g. Sella muds: 1195ppb Hg, 528ppm Cr, 385 ppm Cd, 114 ppm
Ag, etc). The desiccation of estuarine sediments seems to promote the leaching
of heavy metals. Their mobility may be increased by the significant drop of pH.
The recovery of large areas of currently reclaimed salt marshes and, therefore, the
accumulation of metals in their natural sediments could be one of the solutions to decrease
the high heavy metal concentrations in the transitional water of the Cantabrian
Sea.
Key words: heavy metals; salt marshes; reclamation; salt marshes restoration |
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