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Use of NOx - microsensors to estimate the activity of sediment nitrification and NOx - consumption along an estuarine salinity, nitrate, and light gradient

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Microprofiles of nitrate plus nitrite (NOx -) were measured in sediment cores sampled at 6 stations along a nitrate and salinity gradient and a depth transect in Randers Fjord, Denmark. Rates of NOx - production and consumption were calculated from the concentration profiles to describe the variation of these processes under in situ conditions. A microscale biosensor for NOx - was used to obtain NOx - profiles in darkness and under in situ light conditions. This new tool for nitrate plus nitrite measurements in saline environments made it possible to measure NOx - profiles with submicromolar resolution and without interference from chemical species other than nitrous oxide. The NOx - concentration in the inner and middle part of the estuary was very high (55 to 220 μM). The range of NOx - consumption rates found here (47 to 577 μmol N m-2 h-1) were within the range of denitrification rates found in similar environments (measured by 15N isotope techniques). The NOx - concentration in the water was low at the outermost part of the estuary, and all NOx - diffusing into the sediment was consumed in the oxic zone (top 1 mm) of the sediment. In this study, NOx - consumption was not closely coupled to nitrification and depended mostly on NOx - (mainly nitrate) from the overlying water. The NOx - consumption rates were correlated with NOx - concentration in the overlying water, but the sediment was a sink for NOx - only at the highest NOx - concentrations. The effect of changing light conditions on NOx - consumption was significant at the station with the highest NOx - level but not at other stations.

Original languageEnglish
JournalAquatic Microbial Ecology
Pages (from-to)181-193
Number of pages13
Publication statusPublished - 5 Dec 2001

    Research areas

  • Nitrate biosensor, Nitrogen transformation

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