A Century of sediment metal contamination of Mar Menor, Europe's largest saltwater lagoon

Coastal enclosed ecosystems, such as lagoons, are vulnerable to anthropogenic impacts because they favor the accumulation of contaminants from the surrounding watersheds, particularly in their sediments. Europe's largest saltwater lagoon, the Mar Menor (SE, Iberian Peninsula), is a highly impacted ecosystem and the first in the continent to be granted personhood rights. Based on a high-resolution spatial and temporal dataset, we present the historical reconstruction of metal contamination in this ecosystem during the last century. Our results highlight that sediment metal contamination has been mainly driven by the development of the mining industry in the nearby Sierra Minera de Cartagena-La Unión in the late 19th and until the mid-20th century when premeditated mining spills were forbidden. Runoff from former mining areas still transported metals to the lagoon even after mining ceased in the 1990s. The southern sector of the lagoon, closest to mining-affected ephemeral streams, is the most impacted by metal contamination and holds the highest metal stocks. Stocks since 1900 for the entire lagoon reached values of 9200, 1.6, 450, 270, 10,000, and 12 tons of Pb, Hg, As, Cu, Zn, and Ag, respectively. Maxima concentrations were reached in the mid-20th century, with values of 3400, 0.53, 100, 50, 3700, and 5.5 mg·kg-1 for Pb, Hg, As, Cu, Zn, and Ag. Afterward, while some metals' concentrations declined, others were still supplied to the sediments through runoff from former mining areas and sources related to urban expansion. Metal concentrations reported in this study surpass sediment quality guidelines and are generally higher than those found in similar ecosystems globally. Current surface metal concentrations are lower than during most of the 20th century, and sediments seem to retain metal stocks effectively. However, climate change and eutrophication could increase the risk of metal remobilization, further impacting this already vulnerable ecosystem. This study emphasizes the need for attention to managing coastal enclosed ecosystems, where global change impacts can exacerbate the impact of legacy contamination.

This work was funded by the Agencia Estatal de Investigación (AEI) of the Spanish Ministry of Science and Innovation through the OPAL project (PID2019-110311RB-C21) and the WINDERS project (TED2021- 130710B-I00). This work contributes to the María de Maeztu Programme (CEX2019-000940-M) for Units of Excellence of the Spanish Ministry of Science and Innovation. I.A-M acknowledges financial support from FPI grant PRE2020-092343. A.A-O acknowledges support from MCIN/AEI RYC2021-034455-I. J. R-P acknowledges financial support from FPU grant FPU20/01369. I. A-M, V. R., A. A-O., J. R-P. and J. G-O. belong to the consolidated group Marine and Environmental Biogeosciences Research Group - MERS, funded by grant 2021-SGR 00640 from the Direcció General de Recerca. A.P. belongs to the consolidated research group on littoral and oceanic processes, funded by grant 2021SGR 00433 from Generalitat de Catalunya. C. G-R thanks the sabbatical fellowship awarded by PASPA-DGAPA from Universidad Nacional Autónoma de México. M. D-F acknowledges financial support from grant JDC2022-050316-I funded by MCIN/AEI/10.13039/ 501100011033 and by the European Union - NextGenerationEU/PRTR, and support from the Grup d’Hidrologia Subterrània - GHS (Universitat Politècnica de Catalunya) funded by grant 2021-SGR 00609 from Generalitat de Catalunya. This work is contributing to the ICM ’Center of Excellence’ Severo Ochoa (grant CEX2024-001494-S funded by Spanish Agency of Investigation grant AEI 10.13039/501100011033). This work is also part of the THINKINAZUL programme supported by the Spanish Ministry of Science and Innovation with funding from European Union NextGenerationEU (PRTR-C17.I1) and by Fundación Séneca with funding from Comunidad Autónoma Región de Murcia (CARM) (Spain). A. G. B. acknowledges funding from MerTerMar (PID2019-III722RJI00).

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