Trace metal level variation under strong wind conditions and sediment resuspension in the waters of a coastal lagoon highly impacted by mining activities

Abstract

The levels of metals in the waters of the Mar Menor lagoon are higher in the southern than in the northern zone both in the dissolved (As: 1.78 μg L^-1 north vs 1.86 μg L^-1 south; Cd: 0.020 μg L^-1 vs 0.055 μg L^-1; Pb: 0. 686 μg L^-1 vs 2.714 μg L^-1; Zn: 3.06 μg L^-1 vs 10.2 μg L^-1) as in the particulate fraction (As: 13.6 μg g^-1 north vs 27.3 μg g^-1 south; Cd: 0.510 μg g^-1 vs 2.11 μg g^-1; Pb: 146 μg g^-1 vs 575 μg g^-1; Zn: 266 μg g^-1 vs 729 μg g^-1). This difference is associated to the influence of historical and recent inputs from the Sierra Minera Cartagena -La Unión located south of the lagoon. Strong winds cause sediment resuspension in this shallow lagoon, increasing metal levels in the dissolved (twofold) and especially in the particulate fraction (threefold) because the resuspended sediments are rich in metals. Distribution among dissolved and particulate fraction is determined by the chemistry of each element and salinity. This increase causes the levels to reach limits very close to those established by the Water Framework Directive, especially in the case of lead, whose annual average level of 1.23 μg L^-1 is very close to the 1.3 μg L^-1 established in the Directive. Therefore, slight change in environmental variables could make Pb levels to exceed legal limits. Future work should focus on investigating how unique environmental events, enhanced by global change, affect metal cycles in highly anthropised coastal areas.

Keywords: Coastal lagoon; Global change; Metals; Resuspension; Water framework directive.