Sanz et al. (2026) Anthropogenically-induced saline wetland recharge drives denitrification: Implications for nitrate attenuation in semi-arid aquifer–wetland systems

Identification

• Journal: Journal of Contaminant Hydrology
• Year: 2026
• Date: 2026-01-09
• Authors: D. Sanz, D. Salcedo, B. Toledo, I. Dountheva, R. Margalef-Martí, N. Otero, A. Soler, J.J. Gómez-Alday
• DOI: 10.1016/j.jconhyd.2026.104840

Research Groups

• Biotechnology and Natural Resources Section, Institute for Regional Development (IDR), University of Castilla–La Mancha (UCLM), Albacete, Spain.
• Grup MAIMA, SGR Mineralogia Aplicada, Geoquímica i Hidrogeologia (MAGH), Departament de Mineralogia, Petrologia i Geologia Aplicada, Universitat de Barcelona (UB), Spain.
• Institut de Recerca de l'Aigua, Universitat de Barcelona (UB), Spain.

Short Summary

This study demonstrates that the hydrogeological shift of hypersaline wetlands from discharge to recharge zones, caused by intensive irrigation, triggers density-driven flow that facilitates heterotrophic denitrification. This process acts as a natural buffer, attenuating high nitrate concentrations in semi-arid aquifer systems.

Objective

• To evaluate how anthropogenically induced groundwater recharge and density-driven flow from hypersaline wetlands influence nitrate transport and attenuation (denitrification) in semi-arid aquifers.

Study Configuration

• Spatial Scale: The closed hydrogeological basin of the Tirez and Peñahueca hypersaline lagoons, covering 44.23 km² in Central Spain.
• Temporal Scale: Analysis of historical monitoring data (1976–2014) and field campaigns conducted during the 2019–2021 hydrological years.

Methodology and Data

• Models used: Conceptual hydrogeological models of flow reversal, density-driven convective cell analysis, and isotopic fractionation equations for estimating denitrification percentages.
• Data sources: Piezometric measurements, Electrical Resistivity Tomography (ERT) profiles (Wenner-Schlumberger configuration), and multi-isotopic characterization of water samples (δ15N–NO₃⁻, δ18O–NO₃⁻, δ13C–DIC, δ34S–SO₄²⁻, δ18O–SO₄²⁻, δ2H–H₂O, and δ18O–H₂O).

Main Results

• Nitrate (NO₃⁻) concentrations in groundwater increased from ~25 mg/L in the 1990s to over 200 mg/L (maximum 245 mg/L) by 2021 due to agricultural intensification.
• Intensive groundwater abstraction for irrigation reversed hydraulic gradients, creating a 3–10 m vertical disconnection between the lagoons and the aquifer, transforming the wetlands into recharge areas.
• ERT profiles revealed density-driven flow of hypersaline water into the underlying aquifer, which transports dissolved organic carbon (DOC) and creates micro-anoxic environments.
• Multi-isotopic evidence (coupled enrichment of δ15N–NO₃⁻ and δ18O–NO₃⁻ alongside δ13C–DIC depletion) confirmed that heterotrophic denitrification is the primary nitrate attenuation process.
• Maximum estimated denitrification rates reached up to 73% in specific reaction zones at the freshwater–saltwater interface.

Contributions

• Provides a novel link between anthropogenically induced saline recharge and the enhancement of natural nitrate attenuation through density-driven flow.
• Offers a multidisciplinary framework (combining geophysics, hydrochemistry, and isotopes) to identify and quantify biogeochemical reaction zones in complex semi-arid environments.
• Demonstrates the resilience of hypersaline wetland systems in acting as natural barriers against agricultural pollution despite significant hydrological degradation.

Funding

• ADVANCE4WATER-ISOTRACE-ATRAPA projects (PID2022-139911OB-C4-01; PID2022-139911OB-C44) funded by MICIU/AEI/10.13039/501100011033/FEDER, UE.
• ANCOR-TECH project (SBPLY/21/180501/000055) funded by the Junta de Comunidades de Castilla-La Mancha.
• European Union's Horizon 2020 research and innovation programme (Marie Sklodowska-Curie grant No 837873).
• University of Castilla–La Mancha (UCLM) Consolidate Research Group (2023-GRIN-34228).

Citation

@article{Sanz2026Anthropogenicallyinduced,
  author = {Sanz, D. and Salcedo, D. and Toledo, B. and Dountheva, I. and Margalef-Martí, R. and Otero, N. and Soler, A. and Gómez-Alday, J.J.},
  title = {Anthropogenically-induced saline wetland recharge drives denitrification: Implications for nitrate attenuation in semi-arid aquifer–wetland systems},
  journal = {Journal of Contaminant Hydrology},
  year = {2026},
  doi = {10.1016/j.jconhyd.2026.104840},
  url = {https://doi.org/10.1016/j.jconhyd.2026.104840}
}

Generated by BiblioAssistant using gemini-3-flash-preview (Google API)