Heavy metals in Oka river sediments (Urdaibai National Biosphere Reserve, northern Spain): lithogenic and anthropogenic effects |
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| Authors: | M J Irabien F Velasco |
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| Institution: | (1) Department of Mineralogy and Petrology, University of the Basque Country, PB 644, I-48080 Bilbao, Spain, ES |
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| Abstract: | The Oka River basin is located in the Urdaibai National Biosphere Reserve, North Spain. In order to obtain a preliminary
view of its environmental conditions, nitric acid extractable Fe, Mn, Zn, Pb, Cu, Cr, Ni and Co, organic matter content (L.O.I.),
geochemical fractionation of heavy metals and mineralogical composition were analysed in surficial sediments (fraction <63 μm)
collected in October 1991. Relatively high concentrations of metals occurred in a sampling site upstream, due to a local natural
enrichment controlled by weathering of volcanic rocks. Geochemical fractionation confirmed the lithogenic origin of metals,
which were mainly associated to the detrital phase. The significant increase of heavy metals found in some samples collected
in the municipal area of Gernika suggested a pollution effect, related to anthropogenic wastes. Large amounts of metallic
slags have been found mixed with the sediments upstream from this locality. Nevertheless, in view of their composition, it
is unlikely that these slags constitute a significant source of heavy metals in the studied area. In a second sampling in
October 1997 an apparent decreasing trend in some heavy metal levels was noted, particularly for Pb and Cu. Nowadays, enrichment
factors relative to background values confirm moderate anthropogenic influence on Zn, Pb, Cu, Cr and Ni concentrations. However,
heavy metal levels in the Oka river sediments are much lower than those detected in other major rivers of the Basque Country
(Nervión, Urumea, Deba).
Received: 7 July 1997 · Accepted: 4 July 1998 |
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| Keywords: | Oka River Spain Sediments Heavy metals Geochemical fractionation Lithogenic effects Anthropogenic inputs |
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