View article

Viable indicators of nitrogen (N) attenuation at the catchment scale are needed in order to sustainably manage global agricultural intensification. We hypothesized that the dominance of a single land use (pasture production) and strong ground‐to‐surface water connectivity would combine to create a system in which surface water nitrate isotopes (δ¹⁵N and δ¹⁸O of ) could be used to monitor variations in catchment‐scale attenuation. Nitrate isotopes were measured monthly over a 2 year period in four reaches along a spring‐fed, gaining stream (mean ‐N of 6 mg L⁻¹) in Canterbury, New Zealand. The stream water pool indicated that the highest degree of denitrification occurred in the shallow upper reaches. Moving downstream through increasingly sandy soils, the isotopic signature of denitrification became progressively weaker. The lowest reaches fell into the expected range for produced from the nitrification …