Affiliation:
1. Department of Ecology and Genetics, University of Aarhus, Ny Munkegade, DK-8000 �rhus C, Denmark
Abstract
Microzonation of denitrification was studied in stream sediments by a combined O
2
and N
2
O microsensor technique. O
2
and N
2
O concentration profiles were recorded simultaneously in intact sediment cores in which C
2
H
2
was added to inhibit N
2
O reduction in denitrification. The N
2
O profiles were used to obtain high-resolution profiles of denitrification activity and NO
3
−
distribution in the sediments. O
2
penetrated about 1 mm into the dark-incubated sediments, and denitrification was largely restricted to a thin anoxic layer immediately below that. With 115 μM NO
3
−
in the water phase, denitrification was limited to a narrow zone from 0.7 to 1.4 mm in depth, and total activity was 34 nmol of N cm
−2
h
−1
. With 1,250 μM NO
3
−
in the water, the denitrification zone was extended to a layer from 0.9 to 4.8 mm in depth, and total activity increased to 124 nmol of N cm
−2
h
−1
. Within most of the activity zone, denitrification was not dependent on the NO
3
−
concentration and the apparent
K
m
for NO
3
−
was less than 10 μM. Denitrification was the only NO
3
−
-consuming process in the dark-incubated stream sediment. Even in the presence of C
2
H
2
, a significant N
2
O reduction (up to 30% of the total N
2
O production) occurred in the reduced, NO
3
−
-free layers below the denitrification zone. This effect must be corrected for during use of the conventional C
2
H
2
inhibition technique.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
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