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Nitrate isotope data interpreted in combination with hydrological and chemical data provide valuable information on the nitrate pollution sources and on the processes nitrate has undergone during its retention and transport in the watershed. This information is useful for the development of an appropriate water management policy.

The aim of our research was to compare d 11 B measurements performed with thermal ionization mass spectrometry (TIMS) and sector field-inductively coupled plasma-mass spectrometry (SF-ICP-MS) and evaluate the feasibility of implementing stable isotope methods in European water framework directive (WFD) monitoring programs. The comparison was based on d B measurements attainable with SF-ICP-MS, 2s¼ AE 2.6&; (n ¼ 192), is as expected lower than the precision achieved by TIMS, 2s¼ AE 0.3& (n ¼ 183). However the ease of use, rapidity and availability of SF-ICP-MS on one hand and the observed variability in d 11 B in ground-and surface water on the other (from À3.4 to +37&), demonstrates that using SF-ICP-MS as an isotopic screening method would promote the use of isotopic methodology for WFD monitoring. Based on the results of the different case studies it is shown that retrieving precise information on the identification of pollution sources from d11 B values requires reaching the best analytical precision and accuracy possible. Hence, the superior precision of TIMS advantages tracing of nitrate pollution sources. However for some cases, e.g. trying to decipher contributions between sources with really distinct d 11 B signatures (e.g. manure and sewage effluent), SF-ICP-MS results lead to the same conclusions and can therefore be used as a first approachable screening method for the determination of d 11 B in WFD monitoring programs.

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