THE USE OF A MATHEMATICAL-MODEL TO EVALUATE MERCURY ACCUMULATION IN SEDIMENTS AND RECOVERY-TIME IN A COASTAL LAGOON (RIA-DE-AVEIRO, PORTUGAL)

The urge of restoration and management of vital ecosystems (mainly tho se that affect directly human health) has become one of the most reque sted priorities. Ria de Aveiro (a lagoon on the north-western coast of Portugal) has an important economic role in local and surrounding are as due to its variety of resources. Studies have shown that there is a n effective risk of hindering traditional activities due to high level s of mercury. Mercury concentrations in 1985 ranged from 0.7 mu g g(-1 ) to 850 mu g g(-1) in surface sediments and concentrations up to 25 m u g 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 industri al discharges tin 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 exponential ly due to both deposition of mercury free particles and resuspension o f less and less contaminated particles. The model estimated levels act ually measured along the channel and evaluated that, even after 40 yea rs, mercury concentration would be approximately 50 mu g g(-1) in the most contaminated section of that channel if the discharges were disco ntinued now.