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Appl. Environ. Microbiol., Dec 1997, 4679-4685, Vol 63, No. 12
BHL Kelso, RV Smith, RJ Laughlin and SD Lennox
Recent studies on Northern Ireland rivers have shown that summer nitrite
(NO(inf2)(sup-)) concentrations greatly exceed the European Union guideline
of 3 (mu)g of N liter(sup-1) for rivers supporting salmonid fisheries. In
fast-flowing aerobic small streams, NO(inf2)(sup-) is thought to originate
from nitrification, due to the retardation of Nitrobacter strains by the
presence of free ammonia. Multiple regression analyses of NO(inf2)(sup-)
concentrations against water quality variables of the six major rivers of
the Lough Neagh catchment in Northern Ireland, however, suggested that the
high NO(inf2)(sup-) concentrations found in the summer under warm,
slow-flow conditions may result from the reduction of NO(inf3)(sup-). This
hypothesis was supported by field observations of weekly changes in N
species. Here, reduction of NO(inf3)(sup-) was observed to occur
simultaneously with elevation of NO(inf2)(sup-) levels and subsequently
NH(inf4)(sup+) levels, indicating that dissimilatory NO(inf3)(sup-)
reduction to NH(inf4)(sup+) (DNRA) performed by fermentative bacteria
(e.g., Aeromonas and Vibrio spp.) is responsible for NO(inf2)(sup-)
accumulation in these large rivers. Mechanistic studies in which
(sup15)N-labelled NO(inf3)(sup-) in sediment extracts was used provided
further support for this hypothesis. Maximal concentrations of
NO(inf2)(sup-) accumulation (up to 1.4 mg of N liter(sup-1)) were found in
sediments deeper than 6 cm associated with a high concentration of
metabolizable carbon and anaerobic conditions. The (sup15)N enrichment of
the NO(inf2)(sup-) was comparable to that of the NO(inf3)(sup-) pool,
indicating that the NO(inf2)(sup-) was predominantly NO(inf3)(sup-)
derived. There is evidence which suggests that the high NO(inf2)(sup-)
concentrations observed arose from the inhibition of the DNRA
NO(inf2)(sup-) reductase system by NO(inf3)(sup-).
Copyright © 1997, American Society for Microbiology
Dissimilatory Nitrate Reduction in Anaerobic Sediments Leading to River Nitrite Accumulation
Department of Agricultural and Environmental Science, The Queen's University of Belfast, and Agricultural and Environmental Science Division, and Biometrics Division, The Department of Agriculture for Northern Ireland, Belfast, BT9 5PX, United Kingdom
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