76 Contaminants Near Groundwater-Surface Water Interfaces

Groundwater-surface water interfaces influence the transport and fate of contaminants in groundwaters and surface waters. Thus, learning about the behavior and interactions at and near the interfaces are important for understanding hydrogeochemical cycles as well as groundwater and watershed management.

Monday, 20 October 2025
8:00 AM - 12:00 PM
HBGCC, 209

An improved apportionment of nitrate sources in a groundwater system impacted by multiple anthropogenic stressors

Paper number: 76-8
Program: Technical Sessions
Time: 10:00 AM – 10:15 AM

Authors

Abstract

This study focuses on the groundwater system of the Mediterranean coastal agricultural area of Guenniche (Tunisia) that experiences substantial nitrate (NO3) contamination from various anthropogenic sources. Multiple isotopic tracers with a Bayesian isotope MixSIAR model are used to identify the sources of NO3 and to quantify their contributions within the investigated groundwater system. First, a clustering approach is developed for classifying groundwater samples that are controlled by a common mixing of NO3-containing groundwaters. Second, NO3 source identification is proceeded based on δ15NNO3, δ18ONO3 and δ11B isotope tracers. Third, MixSIAR model is constrained by selective NO3 sources and site-specific isotope fractionation effects. Fourth, a separate NO3 sources apportionment processing is undertaken for different clustered groundwater samples. The clustering process determined four different clusters, in which mixing in three clusters is controlled by two NO3 sources (i.e., manure/sewage for two clusters, and manure/synthetic fertilizers for one cluster), whereas the fourth cluster is governed by mixing of three NO3 sources (i.e., manure, sewage, and synthetic fertilizers). Here, manure is observed as the predominant source contributing NO3 to groundwater according to the MixSIAR models, but with different contributions varying from 61 to 71%; consistent with land use of the study area. Ultimately, the approach presented in this study helps to constrain mitigation strategies to selective sites, rather than a general strategy applied to the whole study area.

Geological Society of America Abstracts with Programs. Vol. 57, No. 6

doi: 10.1130/abs/2025AM-411962

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