Nitrate source apportionment in groundwater using Bayesian isotope mixing model based on nitrogen isotope...

Area of Science:

• Environmental Science
• Hydrogeology
• Isotope Geochemistry

Background:

• Groundwater nitrate (NO3-) pollution is a significant environmental concern.
• Accurate source identification is crucial for effective remediation strategies.
• Nitrogen (N) isotopes and isotopic enrichment factors (ɛp/s) are vital for understanding N cycling and NO3- apportionment.

Purpose of the Study:

• To quantitatively analyze groundwater NO3- sources using stable isotopes and Bayesian modeling.
• To calculate ɛp/s values for atmospheric deposition (AD), soil nitrogen (SN), chemical fertilizers (CF), and manure and sewage (M&S) for the first time.
• To assess the influence of cropping systems on NO3- source contributions.

Main Methods:

• Stable isotope analysis of groundwater (δ15N-NO3- and δ18O-NO3-).
• Application of the Bayesian isotope mixing model (SIAR).
• Calculation of nitrogen isotopic enrichment factors (ɛp/s) for different sources.

Main Results:

• Calculated ɛp/s values: AD (0.0‰), SN (-8.7‰), CF (-8.7‰), M&S (14.7‰).
• Demonstrated that isotopic fractionation improves NO3- source apportionment accuracy.
• Identified dominant NO3- sources varied by cropping system: vegetable areas (CF 54.32%, SN 37.75%) and grain areas (SN 33.67%, CF 33.27%, M&S 30.16%).

Conclusions:

• Isotopic fractionation is a powerful tool for accurate groundwater NO3- source apportionment.
• Cropping systems significantly influence the relative contributions of different NO3- sources.
• The study provides critical data for managing groundwater quality in agricultural regions.