『Abstract
Groundwater nitrification is a poorly characterized process affecting
the speciation and transport of nitrogen. Cores from two sites
in a plume of contamination were examined using culture-based
and molecular techniques targeting nitrification processes. The
first site, located beneath a sewage effluent infiltration bed,
received treated effluent containing O2 (＞300μM)
and NH4+(51-800μM). The second
site was 2.5 km down-gradient near the leading edge of the ammonium
zone within the contaminant plume and featured vertical gradients
of O2, NH4+,
and NO3- (0-300, 0-500, and 100-200μM
with depth, respectively). Ammonia- and nitrite-oxidizers enumerated
by the culture-based MPN method were low in abundance at both
sites (1.8 to 350 g-1 and 33 to 35,000 g-1,
respectively). Potential nitrifying activity measured in core
material in the laboratory was also very low, requiring several
weeks for products and 16S rDNA sequencing) detected primarily
sequences associated with the Nitrosospira genus throughout
the cores at the down-gradient site and a smaller proportion from
the Nitrosomonas genus in the deeper anoxic, NH4+
zone at the down-gradient site. Only a single Nitrosospira
sequence was detected beneath the infiltration bed. Furthermore,
the majority of Nitrosospira-associated sequences represent
an unrecognized cluster. We conclude that an uncharacterized group
associated with Nitrosospira dominate at the geochemically
stable, down-gradient site, but found little evidence for Betaproteobacteria
nitrifiers beneath the infiltration beds where geochemical conditions
were more variable.
Keywords: Groundwater; Nitrification; PCR; Ammonium; Nitrate』
1. Introduction
2. Field site and sampling
2.1. Site description
2.2. Sample collection
3. Laboratory incubations and molecular analyses
3.1. Potential nitrification activity and culture-based nitrifier
enumeration
3.2. DNA extraction and molecular techniques
4. Results
4.1. Groundwater chemistry
4.2. Sediment core incubations
4.3. Molecular analysis of extracted DNA
5. Discussion
6. Conclusions
Acknowledgements
References