Investigation of a dual-isotope approach to trace nitrate sources in groundwater systems
Abstract
Nitrate contamination in groundwater has long been an issue in Europe, with reported high nitrate concentrations in drinking water of greater than 10 mg/L NO3-N, as defined by the World Health Organisation, posing various health risks. Identifying the sources and fate of nitrate in groundwater is part of the solution to nitrate contamination. Several methods have been reported for identifying nitrogen sources, such as the single isotope method using the nitrogen isotopes of nitrate, but the methods present difficulties, such as ambiguity of interpretation. In this study, and by adopting a dual-isotope approach, with measurements of oxygen as well as nitrogen isotopes of nitrate, we have been able to identify the sources and fate of nitrate in groundwater with greater confidence. To investigate the approach, we collected groundwater samples from a Pleistocene alluvial aquifer at a bank filtration site in Germany, the Cretaceous Chalk aquifer in rural eastern England, the Triassic sandstone aquifer in the urban English Midlands and also from controlled laboratory columns treated with pig manure. The values of nitrogen isotopes in groundwater nitrate sources were in the range of -0.13 to +5.64 % for inorganic fertiliser, +9.26 to +11.44 % for urban sewerage and +8.99 to +13.61 % for pig manure. Values of the oxygen isotopes in groundwater nitrate sources were in the range of +3.46 to +16.00 % for inorganic fertiliser, +8.21to +10.77 % for sewerage and +10.73 to +12.07 % for pig manure. We also observed that those sites experiencing denitrification produced a linear relationship indicating an enrichment of the heavier nitrogen isotope relative to the heavier oxygen isotope by a factor of 1.3 and 1.9.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.H12C0936F
- Keywords:
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- 1040 Isotopic composition/chemistry;
- 1806 Chemistry of fresh water;
- 1831 Groundwater quality