Biogeochemistry of sediments from restricted exchange environments of Kandalaksha Bay, White Sea, Russian Arctic

Abstract. The White Sea of Russian Arctic is characterized by extreme diversity of enclosed estuarine systems that are often sites of unique biota. The present study focuses on surface sediments from representative restricted exchange environments of the inner part of Kandalaksha Bay, adjacent to the Karelian shore of the White Sea. The TOC and n-alkanes distribution study revealed the major input of terrestrial organic matter into the sediments from higher plants and minor presence of autochthonous microbial sources. Metal (Fe, Mn, Cu, Zn, Cr and Pb) forms study showed that metals in sediments occur mainly in a biogeochemically stable mineral-incorporated form, which comprises up to 98% of total metal content, while labile (acid soluble) and organically bound (alkali soluble) forms make up to 3–11% and 2–12% of total metal content, respectively. Presumably, the major part of both acid soluble and alkali soluble forms is comprised of metals associated with easily soluble amorphous Fe-oxides and bound to sediment organic matter. According to sediment quality guidelines, all trace-metal contents were below the threshold levels. Among sites studied, the heightened contents of bioavailable metal forms are related to sediments enriched in organic matter and/or located within the sea-fresh water barrier zones. The elements studied may be arranged in the following decreasing sequence according to their potential bioavailability: Cu > Zn > Mn > Fe > Cr > Pb. The present study can serve as a basis for comprehensive environmental assessment of the region and objective anoxia prognosis in Arctic ecosystems, while the role of microbial community in element speciation in sediments needs special attention.