Affiliation:
1. Department of Ecology and Genetics, University of Aarhus, Ny Munkegade, DK-8000 Aarhus C, Denmark
Abstract
Nitrogen and oxygen transformations were studied in a bioturbated (reworked by animals) estuarine sediment (Norsminde Fjord, Denmark) by using a combination of
15
N isotope (NO
3
-
), specific inhibitor (C
2
H
2
), and microsensor (N
2
O and O
2
) techniques in a continuous-flow core system. The estuarine water was NO
3
-
rich (125 to 600 μM), and NO
3
-
was consistently taken up by the sediment on the four occasions studied. Total NO
3
-
uptake (3.6 to 34.0 mmol of N m
-2
day
-1
) corresponded closely to N
2
production (denitrification) during the experimental steady state, which indicated that dissimilatory, as well as assimilatory, NO
3
-
reduction to NH
4
+
was insignificant. When C
2
H
2
was applied in the flow system, denitrification measured as N
2
O production was often less (58 to 100%) than the NO
3
-
uptake because of incomplete inhibition of N
2
O reduction. The NO
3
-
formed by nitrification and not immediately denitrified but released to the overlying water, uncoupled nitrification, was calculated both from
15
NO
3
-
dilution and from changes in NO
3
-
uptake before and after C
2
H
2
addition. These two approaches gave similar results, with rates ranging between 0 and 8.1 mmol of N m
-2
day
-1
on the four occasions. Attempts to measure total nitrification activity by the difference between NH
4
+
fluxes before and after C
2
H
2
addition failed because of non-steady-state NH
4
+
fluxes. The vertical distribution of denitrification and oxygen consumption was studied by use of N
2
O and O
2
microelectrodes. The N
2
O profiles measured during the experimental steady state were often irregularly shaped, and the buildup of N
2
O after C
2
H
2
was added was much too fast to be described by a simple diffusion model. Only bioturbation by a dense population of infauna could explain these observations. This was corroborated by the relationship between diffusive and total fluxes, which showed that only 19 to 36 and 29 to 62% of the total O
2
uptake and denitrification, respectively, were due to diffusion-reaction processes at the regular sediment surface, excluding animal burrows.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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