An improved ion-exchange/diffusion method for 15N isotope tracing analysis of nitrate in surface waters from watersheds

A critical assessment of widely used techniques for nitrate source apportionment in arid and semi-arid regions

“…(Kendall, 1998) introduced the expected ranges of δ 15 N and δ 18 O values of nitrate sources through visual δ 18 O vs δ 15 N cross plots and these have been updated several times (Kendall et al, 2015(Kendall et al, , 2008Xue et al, 2009b). However, the identification of the origin of nitrogen concentrations in groundwater only by using nitrate isotope techniques is complicated due to the presence of mixed input from point and non-point sources and the occurrence of biogeochemical processes (e.g., nitrification, denitrification), in the unsaturated zone and the water body, that may alter the initial isotopic values of the nitrate sources (Chen et al, 2010;Curt et al, 2004;Kendall, 1998).…”