Determining nitrate and sulfate pollution sources and transformations in a coastal aquifer impacted by seawater intrusion—A multi-isotopic approach combined with self-organizing maps and a Bayesian mixing model

Nitrate pollution source apportionment, uncertainty and sensitivity analysis across a rural-urban river network based on δ15N/δ18O-NO3− isotopes and SIAR modeling

“…We used the classical and widely used dual-NO 3 − isotope cross-plot diagram to acquire qualitative information concerning the dominant riverine NO 3 − source to the WRT River network (Hu et al, 2019;Taufiq et al, 2019;Torres-Martínez et al, 2020, 2021bHe et al, 2022). The cross-plot diagram of δ 15 N-NO 3 − versus δ 18 O-NO 3 − showed typical characteristics of NO 3 − pollution sources originating from a mixture of soil nitrogen and municipal sewage (Fig.…”

“…can be determined because one oxygen is derived from atmospheric O 2 and the other two oxygens are derived from ambient H 2 O (Chen et al, 2020;Paredes et al, 2020;Torres-Martínez et al, 2020, 2021bCarrey et al, 2021;Liu et al, 2021;Xuan et al, 2022). Based on the end-member δ 18 O values of 23.50‰ and − 14.16-− 0.92‰ determined for atmospheric O 2 and ambient water (from nearby Fuzhou International Atomic Energy Association station, ~240 km), respectively, we estimated that microbially-produced δ resulting in a simultaneous enrichment of 15 N and 18 O in the residual NO 3 − , along with a corresponding decrease in NO 3 − concentrations (Nestler et al, 2011;Hu et al, 2019;Xuan et al, 2022).…”

Validating the accuracy of multiple sediment fingerprinting methods

“…Some new tracers have emerged in recent studies, such as n‐alkanes (Galoski et al, 2019), compound‐specific stable isotopes (Hirave et al, 2021; Mabit et al, 2018; Upadhayay et al, 2018), and eDNA (Frankl et al, 2022). The optimization of the mixing model may improve the accuracy of the sediment source tracing results to some extent, such as via the choice of data corrections (Collins, Walling, et al, 2010; Koiter et al, 2018) or through the use of Bayesian mixing models based on prior information and conditional probability (Stock et al, 2018; Torres‐Martínez et al, 2021). Composite fingerprinting is indeed an effective method to identify sediment sources in catchments.…”

Tracing nitrate sources and transformations using △17O, δ15N, and δ18O-NO3− in a coastal plain river network of eastern China

“…Determination of nitrate isotopes using the denitrifier method is easier and quicker than previous methods (e.g., ion-exchange, cadmium-azide reduction, and AgNO 3 method). Consequently, δ 15 N/ δ 18 O-NO 3 − are frequently used to assess nitrate sources and transformations (Ji et al, 2017;Biddau et al, 2019;Ostad-Ali-Askari et al, 2019;Torres-Martínez et al, 2020, 2021bWu et al, 2021). The theoretical concept for the dual-isotope approach is the characteristic δ 15 N and δ 18 O-NO 3 − values of nitrate originating from different pollution sources (Paredes et al, 2020).…”