『Abstract
The potential for exploitation of urban aquifers is partly dependent
on understanding the distribution and fate of urban N sources,
such as sewage and fertilisers, that can limit the use of groundwater
for public supplies. To investigate the application of the dual-isotope
approach to understanding that N hydrochemistry of urban groundwater,
this paper presents δ15N-NO3-
and δ18O-NO3- data
collected from two multi-level piezometers in the Sherwood sandstone
aquifer beneath Nottingham in the English Midlands, UK. At one
multi-level piezometer (Old Basford), depth sample measurements
of δ15N-NO3- in the
range +9.2 to +11.4‰ and δ18O-NO3-
in the range +8.2 to +10.9‰, together with NO3-
nitrate concentrations from 31.7 to 66.7 mg/l, are evidence for
nitrification of sewage-derived inputs. In contrast, at the other
multi-level piezometer (the Meadows), isotopically enriched samples
(δ15N-NO3- in the range
+24.3 to +42.2‰ and δ18O-NO3-
in the range +20.5 to +29.4‰) are evidence for denitrification,
although the compositional range of δ15N-NO3-
does not identify the N source without corroborating data. For
the Meadows location, a cross-plot of δ15N-NO3- versus δ18O-NO3-
gave an enrichment of the 15N isotope relative to the
18O isotope by a factor of 1.9, within the range of
1.3-2.1 reported for denitrification in other studies. This study
has shown that the dual-isotope approach provides improved understanding
of N sources and fate in the urban environment but further work
is required to identify nitrification pathways to provide more
confidence in the application and interpretation of δ18O-NO3- measurements.』
1. Introduction
2. Study area
3. Methods and materials
4. Results and discussion
4.1. Old Basford
4.2. The Meadows
5. Conclusions
Acknowledgements
References