Fig. 3: Variation of δ¹⁸O and δ¹⁵N of NO₃⁻ in river waters and groundwater with water temperature (T_w) in °C.

The linear regression of δ¹⁸O-NO₃⁻ (‰) vs T_w (°C) was more significant for groundwater (R² = 0.41) than river waters (R² < 0.02). The results of the linear regression models for panels a–d are in Supplementary Table 5.