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Geological Society, London, Special Publications; 1998; v. 130; p. 23-35;
DOI: 10.1144/GSL.SP.1998.130.01.03
© 1998 Geological Society of London

Identification of the source and fate of nitrate contamination of the Jersey bedrock aquifer using stable nitrogen isotopes

A. R. Green*, N. A. Feast{dagger}, K. M. Hiscock & P. F. Dennis

School of Environmental Sciences, University of East Anglia, Norwich, NR4 7TJ, UK

Measured NO3– concentrations in the Jersey bedrock aquifer exceeded 50 mg l–1 in 67% of groundwaters sampled in June 1995. The {delta}15N values of this dissolved NO3– showed a total range in composition from + 3.6{per thousand} to + 18.4{per thousand} and exhibited a general, island-wide increase from + 4{per thousand} in the centre of the island to + 9{per thousand} towards coastal districts. The majority of the island is intensively cultivated and most of the sites sampled have {delta}15N values of less than + 7{per thousand} (mean = + 7.7{per thousand}, n = 40) indicative of an agricultural source for NO3–. There is no apparent evidence for point-source contamination from septic tanks. The progressive seaward increase in {delta}15N is attributed to an increasing volume of deeper, denitrified groundwater mixing with shallow groundwater. Values of {delta}15N greater than + 10{per thousand} are restricted to those coastal and valley locations that abstract, due to their low topographic elevation, the greatest proportion of deeper, denitrified groundwater. An alternative explanation is that sewer leakage enhances the observed {delta}15N values in southern urban areas, although this is considered unlikely to be occurring at present.


* Present address: The Environment Agency, Cobham Road, Ipswich IP3 9JE, UK

{dagger} Present address: Shell International Exploration and Production B.V., Volmerlaan 8, P.O. Box 60, 2280 Rijswijk, The Netherlands




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[Abstract] [PDF]