Fig. 2: Distribution of historical daily isotope values in reservoirs.

Daily mean values of δ¹⁵N-NO₃⁻ and δ¹⁸O-NO₃⁻ on each reservoir simulated by ETM+ (from 2006 to 2023) and MSI (from 2019 to 2023) and in-situ measured value. a Simulation results of ETM+ in dry season. b Simulation results of ETM+ in rainy season. c Simulation results of MSI in dry season. d Simulation results of MSI in rainy season. e Statistics of LJ reservoir simulated by ETM+. f Statistics of NS reservoir simulated by ETM+. g Statistics of QW reservoir simulated by ETM+. h Statistics of LJ reservoir simulated by MSI. i Statistics of NS reservoir simulated by MSI. j Statistics of QW reservoir simulated by MSI. In both (a, b, c, d), solid blue dots represent the simulation value of LJ reservoir, the hollow blue dot represents the measured value of LJ reservoir, the solid red squares represent the simulation value of NS reservoir, the hollow red squares represent the measured value of NS reservoir, the solid yellow triangle represent the simulation value of QW reservoir, the hollow yellow triangle represent the measured value of QW reservoir. In both (e, f, g, h, i, j), the light blue part represents the distribution of isotopes in the MS source, the dark blue represents isotopic distribution in NF-SN mixed source, the light yellow part represents the distribution of isotopes in the NF-SN-MS mixed source, the dark yellow part represents the distribution of isotopes in the SN-MS mixed source, where the inner ring is the dry season and the outer ring is the rainy season.