Denitrification in an oligotrophic estuary: a delayed sink for riverine nitrate

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http://hdl.handle.net/10138/230263

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Hellemann , D , Tallberg , P A S , Bartl , I , Voss , M & Hietanen , S S 2017 , ' Denitrification in an oligotrophic estuary: a delayed sink for riverine nitrate ' , Marine Ecology. Progress Series , vol. 583 , pp. 63-80 . https://doi.org/10.3354/meps12359

Title: Denitrification in an oligotrophic estuary: a delayed sink for riverine nitrate
Author: Hellemann, Dana; Tallberg, Petra Astrid Sofia; Bartl, Ines; Voss, Maren; Hietanen, Siru Susanna
Contributor organization: Environmental Sciences
Susanna Hietanen / Principal Investigator
Aquatic Biogeochemistry Research Unit (ABRU)
Marine Ecosystems Research Group
Date: 2017-11-16
Language: eng
Number of pages: 18
Belongs to series: Marine Ecology. Progress Series
ISSN: 0171-8630
DOI: https://doi.org/10.3354/meps12359
URI: http://hdl.handle.net/10138/230263
Abstract: Estuaries are often seen as natural filters of riverine nitrate, but knowledge of this nitrogen sink in oligotrophic systems is limited. We measured spring and summer dinitrogen production (denitrification, anammox) in muddy and non-permeable sandy sediments of an oligotrophic estuary in the northern Baltic Sea, to estimate its function in mitigating the riverine nitrate load. Both sediment types had similar denitrification rates, and no anammox was detected. In spring at high nitrate loading, denitrification was limited by likely low availability of labile organic carbon. In summer, the average denitrification rate was similar to 138 mu mol N m(-2) d(-1). The corresponding estuarine nitrogen removal for August was similar to 1.2 t, of which similar to 93% was removed by coupled nitrification-denitrification. Particulate matter in the estuary was mainly phytoplankton derived (> 70% in surface waters) and likely based on the riverine nitrate which was not removed by direct denitrification due to water column stratification. Subsequently settling particles served as a link be tween the otherwise uncoupled nitrate in surface waters and benthic nitrogen removal. We suggest that the riverine nitrate brought into the oligotrophic estuary during the spring flood is gradually, and with a time delay, removed by benthic denitrification after being temporarily ` trapped' in phytoplankton particulate matter. The oligotrophic system is not likely to face eutrophication from increasing nitrogen loading due to phosphorus limitation. In response, coupled nitrification-denitrification rates are likely to stay constant, which might increase the future export of nitrate to the open sea and decrease the estuary's function as a nitrogen sink relative to the load.
Subject: 1172 Environmental sciences
Coastal filter
Northern Baltic Sea
Nitrogen
Sand sediment
Particulate organic nitrogen
Isotope pairing technique
Quark Strait
ANAEROBIC AMMONIUM OXIDATION
ISOTOPE PAIRING TECHNIQUE
STIRRED BENTHIC CHAMBERS
COASTAL MARINE-SEDIMENTS
NORTH-ATLANTIC OCEAN
BALTIC SEA
ORGANIC-MATTER
NITROGEN BIOGEOCHEMISTRY
PERMEABLE SEDIMENTS
SEASONAL OXYGEN
Peer reviewed: Yes
Rights: cc_by
Usage restriction: openAccess
Self-archived version: publishedVersion
Funder: Unknown funder
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