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The nitrogen isotope effect of benthic remineralization-nitrification-denitrification coupling in an estuarine environment

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Author(s): M. Alkhatib | M. F. Lehmann | P. A. del Giorgio

Journal: Biogeosciences Discussions
ISSN 1810-6277

Volume: 8;
Issue: 6;
Start page: 11689;
Date: 2011;
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ABSTRACT
The nitrogen (N) stable isotopic composition of pore water nitrate and total dissolved N (TDN) was measured in sediments of the St. Lawrence Estuary and the Gulf of St. Lawrence. The study area is characterized by gradients in organic matter reactivity, bottom water oxygen concentrations, as well as benthic respiration rates. Benthic N isotope exchange, as well as the nitrate and TDN isotope effects of benthic nitrification-denitrification coupling on the water column, ϵapp and ϵsed, respectively, were investigated. The sediments were a major sink for nitrate and a source of reduced dissolved N (RDN = DON + NH4+). We observed that both the pore water nitrate and RDN pools were enriched in 15N relative to the water column, with increasing δ15N downcore in the sediments. As in other marine environments, the biological nitrate isotope fractionation of net nitrate elimination was barely expressed at the scale of sediment-water-exchange, with ϵapp values
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