The influence of a metal-enriched mining waste deposit on submarine groundwater discharge to the coastal sea

Submarine groundwater discharge (SGD) was investigated at El Gorguel Bay (Cartagena-La Unión Pb-Zn mining district, Murcia, Spain), a Mediterranean region where mine tailings have been accumulated for decades at the shoreline. At this site, groundwater may become enriched in metals prior to discharge to the coastal sea and may lead to significant releases that can contaminate the coastal environment. The distribution of dissolved metals and Ra isotopes were studied in seawater and groundwater samples collected during the summer season in 2013. Cross-shore gradients of 224Ra in the bay allowed the calculation of a SGD flow of (39 ± 14) 103 m3 day−1. SGD-driven metal fluxes were 47-180 mol day−1 km− 1 for Zn, 0.20-0.60 mol day− 1 km− 1 for Pb, 4-32 mol day− 1 km− 1 for Fe, 0.8-2.3 mol day− 1 km− 1 for Cu and 0.9-2.8 mol day− 1 km− 1 for Ni. Compared to other coastal zones not affected by mining activities, SGD-driven metal fluxes were especially significant for dissolved Zn and Pb. The magnitude of these SGD-driven metal fluxes indicates that SGD is a relevant pathway in delivering metals to the coastal environment at El Gorguel Bay. This fact highlights the importance of investigating the role of SGD as a possible source of contamination to the sea in mining districts located in the proximity of the coast.