Assessing the environmental impacts of engineering and agrochemical pollution in a historically-eutrophic estuary: The Mondego case (W Portugal)

Abstract

The Mondego Estuary (W Portugal) experienced a process of eutrophication in the late 20^th century, making it one of the most impacted systems in southern Europe. To examine its recent environmental evolution, sedimentary records were analyzed from a multiproxy approach, involving biotic, sedimentological, geochemical, physical, and radionuclide data. Results evidenced the transformation of the estuary due to anthropogenic cumulative impacts. The closure of the upstream branch triggered rapid ‘continentalization’ in the southern arm, altering the hydrosedimentary regime and favoring eutrophication. However, the middle and lower sectors exhibited stronger marine influences. Foraminiferal biota responded effectively to management interventions to improve hydrodynamics, while showing no discernible ecotoxicological responses to agricultural discharges. Pesticide accumulations patterns are shaped by natural and anthropogenic factors, with strong agrochemical fingerprints in the upper and lower sectors. The topmost 20-cm layer of sediments contain high pesticide concentrations and microplastics, posing challenges for future management and pollutant mitigation.