Department of Biology

Aarhus University Seal

Susanne Nielsen

Intracellular nitrate in sediments of an oxygen-deficient marine basin is linked to pelagic diatoms

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Intracellular nitrate is an important electron acceptor in oxygen-deficient aquatic environments, either for the nitrate-storing microbes themselves, or for ambient microbial communities through nitrate leakage. This study links the spatial distribution of intracellular nitrate with the abundance and identity of nitrate-storing microbes in sediments of the Bornholm Basin, an environmental showcase for severe hypoxia. Intracellular nitrate (up to 270 nmol cm−3 sediment) was detected at all 18 stations along a 35-km transect through the basin and typically extended as deep as 1.6 cm into the sediment. Intracellular nitrate contents were particularly high at stations where chlorophyll contents suggested high settling rates of pelagic primary production. The depth distribution of intracellular nitrate matched that of the diatom-specific photopigment fucoxanthin in the upper 1.6 cm and calculations support that diatoms are the major nitrate-storing microbes in these sediments. In contrast, other known nitrate-storing microbes, such as sulfide-oxidizing bacteria and foraminifers, played only a minor role, if any. Strikingly, 18S rRNA gene sequencing revealed that the majority of the diatoms in the sediment were pelagic species. We conclude that intracellular nitrate stored by pelagic diatoms is transported to the seafloor by settling phytoplankton blooms, implying a so far overlooked ‘biological nitrate pump’.
Original languageEnglish
Article numberfiy122
JournalFEMS Microbiology Ecology
Number of pages12
Publication statusPublished - 2018

    Research areas

  • Bornholm Basin, hypoxia, anoxia, diatoms, large sulfur bacteria, Beggiatoa, Thioploca, photopigments, fucoxanthin, eutrophication, STORAGE, BORNHOLM BASIN, SULFUR BACTERIA, REDUCTION, BALTIC SEA, MINIMUM ZONE, NITROGEN, WATER SEDIMENTS, PHYTOPLANKTON, THIOPLOCA

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