The use of a mathematical model to evaluate mercury accumulation in sediments and recovery time in a coastal lagoon (Ria de Aveiro, Portugal)

Abstract

The urge of restoration and management of vital ecosystems (mainly those that affect directly human health) has become one of the most requested priorities. Ria de Aveiro (a lagoon on the north-western coast of Portugal) has an important economic role in local and surrounding areas due to its variety of resources. Studies have shown that there is an effective risk of hindering traditional activities due to high levels of mercury. Mercury concentrations in 1985 ranged from 0.7 μg g−1 to 850 μg g−1 in surface sediments and concentrations up to 25 μg g−1 fresh weight in fishes. A mathematical model (ECoS) was used to perform a simulation of mercury accumulation in surface sediments along the most contaminated channel from the beginning of the industrial discharges (in the 50's) until present days and recovery time for a zero mercury discharge from 1995 until 2045. The model shows that the amount of mercury in the surface sediments would decrease exponentially due to both deposition of mercury free particles and ressuspension of less and less contaminated particles. The model estimated levels actually measured along the channel and evaluated that, even after 40 years, mercury concentration would be approximately 50 μg g−1 in the most contaminated section of that channel if the discharges were discontinued now.