Tracking Metal Dispersion Pathways in an abandoned Mediterranean Mining Landscape: Cartagena–La Unión mining district Use Case.

The former Cartagena–La Unión (SE Spain) mining district is one of the most heavily impacted mining landscapes in the Mediterranean basin. The area has been mined for over two millennia for sulfide minerals such as galena (PbS), sphalerite (ZnS), and pyrite (FeS), as well as carbonates, iron oxides, hydroxides, and sulfates. Mining activity peaked from the mid-19th century until 1991, when the last mine closed. Today, the landscape retains numerous traces of its mining past, including millions of tons of mine wastes with extremely high metal concentrations (e.g., Pb and Zn frequently > 10,000 mg kg-¹, Cu commonly > 100 mg kg-¹, Mn often >1,500 mg kg-¹, and Cd between 10 and 100 mg kg-¹). Combined with sparse vegetation cover, torrential rainfall events, and persistent winds, these conditions create a highly dynamic system where both water and wind erosion act as major pathways for pollutant transport.

Figure 1. Location of Cartagena–La Unión mining district (SE Spain) and study site where SOILPROM data collection is being implemented for hydric erosion (a) and wind erosion (b).

Within the Horizon Europe project SOILPROM, this site serves as a key use-case for understanding how metals and metalloids are transported and redistributed under real environmental conditions. Our work focuses on a central question: How do erosion processes drive the dispersion of metals in abandoned semi-arid mining areas?

Water Erosion: Storm Events as Drivers of Metal Transport

The Rambla del Beal, an ephemeral watercourse that drains the mining area, plays a key role in the transport of metals. Its channel, heavily affected by mining waste, acts as a major conduit for the transfer of contaminated sediments to lowland areas.

To quantify the transport of polluted sediments by water erosion, field monitoring has been established along a ~1.5 km stretch of the upper section of the Rambla del Beal, focusing on one check dam.

The approach combines:

  • Runoff collectors (PVC pipes) to capture runoff and suspended sediments
  • Erosion nails to measure sediment deposition in the waterbed
  • Sediment core collection to quantify the amount of accumulated material in the waterbed
  • Catchment-scale analysis (slope, vegetation, soil properties)
Figure 2. Panoramic view of the slopes within the catchment draining into the Rambla del Beal, where erosion nails have been installed to evaluate sediment deposition in the waterbed and PVC pipes have also been placed next to the check dam for collecting runoff and suspended sediments.
Figure 3. Details of the PVC pipes (a) for collecting runoff and suspended sediments, erosion nails (b) and core sampling (c) in the Rambla del Beal watercourse.

Four runoff and erosion events were monitored between the summer of 2025 and the spring of 2026. In summer, the extreme dryness of the soil favors the oxidation of sulfides contained in mine wastes, leading to the precipitation of secondary metal sulfates on the surface (Figure 4). When these sulfates dissolve during rainfall events, the resulting runoff is highly saline and acidic, which facilitates the transport of dissolved metals (Figures 5 and 6).

Figure 4. Salt efflorescence formed by secondary sulfates precipitated during the driest periods of the year.
Figure 5. Electrical conductivity (EC) and pH of runoff collected between July 2025 and April 2026.
Figure 6. Soluble metal concentrations in runoff collected between July 2025 and October 2025.

The erosion rates varied between 0.5 and 1.7 t ha⁻¹ (Figures 7 and 8) and the transported sediments contained very high metal concentrations (e.g. Pb: 20,000–40,000 mg kg⁻¹; Zn: 3,000–6,000 mg kg⁻¹) (Figure 8).

Figure 7. Measuring sediment height on the erosion nails after the rainfall event of Oct 2025.
Figure 8. Erosion rates in the events monitored between July 2025 and April 2026.
Figure 9. Total metal concentrations in sediments collected in the PVC pipes after the rainfall events of July 2025 and October 2025.

Water erosion is a major pathway for metal dispersion, acting in two ways:

1) the transport of dissolved metals in runoff;

2) the transport of metals bound to soil particles. Metal dispersion by water erosion has a strong seasonal component due to the formation of sulfate efflorescence during the dry summer period.

Wind Erosion: Atmospheric Pathways of Contamination

In parallel, wind-driven processes are being investigated in flat depositional area located ~6.5 km away near the mouth of the Rambla del Beal, where mine wastes have accumulated over decades (Figure 10).

Figure 10. Location of the flat area for evaluating metal transport by wind erosion.

The experimental setup includes:

  • Ten BSNE (Big Spring Number Eight) dust collectors at multiple heights (5, 25, 50, 75, 100 and 150 cm) (Figure 11)
  • Sampling across dominant wind regimes (Lebeche – SO and Levante – E/NE) (Figure 12)
  • Seasonal monitoring during high-risk periods (summer and spring)
Figure 11. BSNE dust collectors
Figure 12. BSNE dust collectors in the lower section of the Rambla del Beal.

Results demonstrate that wind erosion is a major mechanism for metal dispersion (Figure 13):

Figure 13. Dust sample collection.
  • Dust particles show very high metal concentrations (e.g. Zn ~ 9500 mg kg⁻¹; Pb ~ 8000 mg kg⁻¹; Cu > 100 mg kg-1)
  • En silt fraction dominates, which facilitates long-range transport
  • Wind direction influences both the concentration and variability of transported material

These findings confirm that polluted dust emissions represent not only a local issue, but also a potential regional and atmospheric risk.

From Field Data to Predictive Modelling

A key objective of SOILPROM is to move beyond site-specific observations and develop integrated modelling frameworks. Data from this use case will be provided to modelers at Wageningen University to feed the OpenLISEM model (to simulate metal dispersion by water erosion) and the MicroHH model (to simulate metal dispersion by wind erosion). The integration of field data and modelling will help identify critical transport pathways, quantify pollutant fluxes under different environmental scenarios, and improve predictions of pollutant behavior under changing climate conditions.

These processes are expected to intensify under future climate scenarios characterized by longer drought periods and more extreme rainfall events, particularly in Mediterranean regions. Understanding how climate-driven erosion affects pollutant mobility is therefore essential for anticipating future environmental risks and designing effective mitigation strategies

Supporting Sustainable Remediation Strategies

Understanding how metals and metalloids move through this landscape is essential for designing effective mitigation and restoration measures.

The results obtained in Cartagena–La Unión use case will support evidence-based land management strategies, help prioritize restoration actions such as tailings stabilization and vegetation establishment, and contribute to reducing environmental and human exposure risks.

More broadly, this use-case contributes to SOILPROM’s mission of improving our capacity to assess and manage soil pollution across Europe through integrated, process-based approaches.