『Abstract
On-site disposal of sewage in septic systems can lead to groundwater
plumes with NO3--N concentrations
exceeding the common drinking water limit of 10 mg/L. Currently,
denitrification is considered as the principal natural attenuation
process. However, at a large seasonal-use septic system in Ontario
(256 campsites), a suboxic zone exists where nitrogen removal
of up to 80% occurs including removal of NH4+-N.
This zone has both NO3--N and
NH4+-N at >5 mg/L each. In the
distal NH4+-rich zone, NH4+-N concentrations (8.1±8.0 mg/L)
are lower than in the proximal zone (48±36 mg/L) and NH4+-N
is isotopically enriched (concentration-weighted mean δ15N
of +15.7‰) compared to the proximal zone (+7.8‰). Furthermore,
δ15N-NH4+ isotopic
enrichment increases with depth in the distal zone, which is opposite
to what would result if nitrification along the water table zone
was the mechanism causing NH4+
depletion. Bacterial community composition was assessed with molecular
(DNA-based) analysis and demonstrated that groundwater bacterial
populations were predominantly composed of bacteria from two Candidatus
genera of the Planctomycetales (Brocasia and Jettenia). Together,
these data provide strong evidence that anaerobic ammonium oxidation
(anammox) plays an important role in nitrogen attenuation at this
site.』
Introduction
Long Point site
Methods
Results
Ammonium and nitrate distribution
Microbiology
Discussion
NH4+ breakthrough
NH4+ isotopic behavior
Mechanisms of NH4+ degradation
Anammox reaction rate
Anammox bacteria
Conclusion and implications
Acknowledgments
Supporting information
References