Seawater in the Gulf of Riga is a complicated mixture of freshwater from a large number of rivers andthe inflowing saline waters of the central Baltic Sea.The Daugava River alone gives 65% of freshwater runoff. In all seasons of the year the concentrations of metals were investigated in water (surface and 1 m above sediment) and in sediment samples from the Daugava River, the mixing zone and the Gulf of Riga. Stations were chosen to cover the salinity gradient inside the freshwater plume as well as adjacent waters.
The concentrations of Cu, Zn, Ni, Mn and Fe in water of the Daugava plume zone in the surface layer and in water 1 m above sediments are different, so are the concentrations of metals distinguished in the Daugava River, the mixing zone and the Gulf of Riga. The seasonal variability of concentrations in water is significant for all metals studied. Principal component analysis (PCA) with Varimax rotation of initial factors showed differences among the Daugava River, mixing zone and the Gulf of Riga. In all seasons there was a significant correlation among the concentrations of Hg, Cd, Pb, Cu, Zn, Ni, Mn and Fe in sediments, but only in spring the concentrations of metals in sediments correlated with water salinity and oxygen. The concentrations of metals in water in different zones showed no essential correlation with the physical-chemical parameters.

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2011 - Vol.53
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