Modern conditions and recent environmental evolution of the industrialized inner Ría of Ferrol (Galicia, NW Spain)

Abstract

Galician rías provide several ecosystem services of great ecological and economic significance in the northwestern Iberian margin, requiring a good environmental quality for sustainable harnessing. More paleoenvironmental reconstructions extending to their preindustrial state are needed to predict their evolution under natural and human-induced perturbations, such as ongoing anthropogenic global warming. This study's aim is twofold: first, characterize the current environmental conditions governing the inner Ría of Ferrol (Galicia, NW Spain) and address its recent natural and anthropogenic evolution. Therefore, a multiproxy approach (benthic foraminifera, grain size, pollen content, trace metals, Al, total organic and inorganic carbon contents, total nitrogen content, δ13C, magnetic susceptibility, 210Pb and 137Cs radiotracers, and microplastics) has been applied to intertidal surface and sediment core samples. The benthic foraminiferal results exhibit typical inner ría assemblages, primarily driven by natural ría-estuarine dynamics, with a higher dominance of brackish species (H. germanica, A. morphogroup tepida), fewer living individuals and marine allochthonous taxa toward the continental end-member. The foraminiferal standing crops and surface trace metal concentrations do not reflect strong anthropogenic impacts, although areas with elevated magnetic susceptibility have been detected, probably associated with nearby industrial activities. The recent sedimentary deposits reveal anthropogenic impacts at local and regional scales, with different environmental shifts. Local impacts were triggered by physical interventions in the inner ría, with the construction of the As Pías Bridge in 1968 and the great urban-industrial development of Ferrol city and surrounding localities experienced since the late 19th century. Land-use changes have driven regional scale changes, corresponding to reforestation plans with the introduction of anthropogenic plant species for industrial purposes initiated in the 1940s. The stratigraphic analysis of sediment cores has unveiled high levels of contaminants (Zn and microplastics) in the innermost sector as the primary environmental concerns. In this sediment-infilling and restricted area, potential dredging activities could release them leading to their possible bioavailability. Although past adverse environmental conditions cannot be discarded, sedimentary intervals with negligible presence of microfauna in the innermost area have mostly been attributed to taphonomic processes involving calcareous dissolution and disaggregation of agglutinated tests, likely caused by carbonate-undersaturated conditions and organic matter metabolization by microbial activity respectively.