Fig. 2: δ¹⁸O vs δ¹⁵N of NO₃⁻ in rivers and groundwater.

Symbol size denotes NO₃-N concentration in mg L⁻¹. The δ¹⁸O values are relative to SMOW and normalized to in situ H₂O, as described in Venkiteswaran et al.³¹. The results of the linear regression models of panels a–d are in Supplementary Table 4.