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Applied and Environmental Microbiology, January 1999, p. 61-66, Vol. 65, No. 1
Department of Agricultural and Environmental
Science,
Received 10 June 1998/Accepted 20 October 1998
The contribution of the biochemical pathways nitrification,
denitrification, and dissimilatory NO3
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Effects of Carbon Substrates on Nitrite
Accumulation in Freshwater Sediments
reduction to NH4+ (DNRA) to the accumulation of
NO2
in freshwaters is governed by the species
compositions of the bacterial populations resident in the sediments,
available carbon (C) and nitrogen (N) substrates, and environmental
conditions. Recent studies of major rivers in Northern Ireland have
shown that high NO2
concentrations found in
summer, under warm, slow-flowing conditions, arise from anaerobic
NO3
reduction. Locally, agricultural
pollutants entering rivers are important C and N sources, providing
ideal substrates for the aquatic bacteria involved in cycling of N. In
this study a range of organic C compounds commonly found in
agricultural pollutants were provided as energy sources in 48-h
incubation experiments to investigate if the chemical compositions of
the pollutants affected which NO3
reduction
pathway was followed and influenced subsequent
NO2
accumulation. Carbon stored within the
sediments was sufficient to support DNRA and denitrifier populations,
and the resulting NO2
peak (80 µg of N
liter
1 [approximate]) observed at 24 h was
indicative of the simultaneous activities of both bacterial groups. The
value of glycine as an energy source for denitrification or DNRA
appeared to be limited, but glycine was an important source of
additional N. Glucose was an efficient substrate for both the
denitrification and DNRA pathways, with a NO2
peak of 160 µg of N liter
1 noted at 24 h. Addition
of formate and acetate stimulated continuous NO2
production throughout the 48-h period,
caused by partial inhibition of the denitrification pathway. The
formate treatment resulted in a high NO2
accumulation (1,300 µg of N liter
1 [approximate]),
and acetate treatment resulted in a low NO2
concentration (<100 µg of N liter
1).
*
Corresponding author. Mailing address: Department of
Agricultural and Environmental Science, The Queen's University of
Belfast, Newforge Lane, Belfast BT9 5PX, United Kingdom. Phone: 01232 255490. Fax: 01232 382244. E-mail:
B.KELSO{at}QUB.AC.UK.
Applied and Environmental Microbiology, January 1999, p. 61-66, Vol. 65, No. 1
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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