76-7 An improved apportionment of nitrate sources in a groundwater system impacted by multiple anthropogenic stressors

Session: Contaminants Near Groundwater-Surface Water Interfaces

Presenting Author:

Lamine Boumaiza

Authors:

Boumaiza, Lamine¹, Ben Ammar, Safouan², Chesnaux, Romain³, Mayer, Bernhard⁴, Sacchi, Elisa⁵, Huneau, Frédéric⁶, Garel, Émilie⁷, Johannesson, Karen⁸, Stotler, Randy⁹, Khouatmia, Mohamed¹⁰, Nlend, Bertil¹¹, Knöller, Kay¹², Stumpp, Christine¹³

(1) University of Texas at Austin, Austin, USA, (2) Université de Carthage, Tunis, Tunisia, (3) Université du Québec à Chicoutimi, Saguenay, Canada, (4) University of Calgary, Calgary, Canada, (5) University of Pavia, Pavia, Italy, (6) Université de Corse, Corse, France, (7) Université de Corse, Corse, France, (8) University of Massachusetts Boston, Boston, USA, (9) University of Waterloo, Waterloo, Canada, (10) National Center of Nuclear Sciences and Technologies, Tunis, Tunisia, (11) Université de Douala, Douala, Cameroon, (12) Helmholtz Centre for Environmental Research, Halle, Germany, (13) University of Natural Resources and Life Sciences, Vienna, Austria,

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 δ¹⁵N_NO3, δ¹⁸O_NO3 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 Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-4613

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