Present limitations and future prospects of stable isotope methods for nitrate source identification in surface- and groundwater

Nitrate (NO3-) contamination of surface- and groundwater is an environmental problem in many regions of the world with intensive agriculture and high population densities. Knowledge of the sources of NO3- contamination in water is important for better management of water quality. Stable nitrogen ((delta N-15) and oxygen (delta O-18) isotope data of NO3- have been frequently used to identify NOT sources in water. This review summarizes typical delta N-15- and delta O-18-NO3- ranges of known NO3- sources, interprets constraints and future outlooks to quantify NO3- sources, and describes three analytical techniques (ion-exchange method, bacterial denitrification method, and cadmium reduction method) for delta N-15- and delta(18) O-NO3- determination. Isotopic data can provide evidence for the presence of dominant NO3- sources. However, quantification, including uncertainty assessment, is lacking when multiple NOT sources are present. Moreover, fractionation processes are often ignored, but may largely constrain the accuracy of NO3- source identification. These problems can be overcome if (1) NOT isotopic data are combined with co-migrating discriminators of NOT sources (e.g. B), which are not affected by transformation processes, (2) contributions of different NO3- sources can be quantified via linear mixing models (e,g. SIAR), and (3) precise, accurate and high throughput isotope analytical techniques become available. Crown Copyright (C) 2009 Published by Elsevier Ltd. All rights reserved.