Metal concentrations in blue mussel (Mytilus edulis) in the Kaldvellfjord, Lillesand county, affected by metal rich runoff.

Abstract

In this master thesis there has been studied possible effects from acidic, metalrich runoff on blue mussels (Mytilus edulis) in the Kaldvellfjord (Lillesand county), as a result of sulphide oxidation from deposits in the precipitation area with sulphide-containing bedrock. Blue mussels from 6 stations and two depths 1 and 5 m were investigated at different times in 2014. Al, Fe and Mn exhibited the highest concentrations during high freshwater runoffs in both water and blue mussels at 1 m depth. Also at 1 m depth, all investigated metal concentrations in water had positive correlations with runoff. For blue mussels most of the metals showed the same positive correlation pattern. The results were compared to the Norwegian pollution guidelines for metal concentrations in water and soft tissue from blue mussels. The median metal concentrations from the Kaldvellfjord showed polluted values, though the stream Stordalsbekken had periodically values within the most polluted category. Water samples from 1m depth in the Kaldvellfjord showed significant higher concentrations than the samples from 5m depth. The concentrations in blue mussels did not show any critical values, although higher concentrations were found in small mussels (20-35 mm) compared to big mussels (>36 mm) in addition to the higher concentrations at 1 m compared to 5 m. High concentration inputs of inorganic dissolved Al from strongly acidified streams are the factor of most biological concern for this fjord, especially near the fresh water outlets. When the fjord with high pH and poor metal concentrations is supplied with metal rich freshwater with low pH, several metals will start to polymerize and precipitate. Among metals, aluminum is known to be very toxic to many gill-breathing organisms during polymerization/precipitation conditions. This may be the reason for the blue mussel mortality seen near acidic, metal rich stream outlets in the Kaldvellfjord. As polymerization/precipitation are very unstable processes, it is difficult to both measure and model the actual chemical conditions. During conditions like this, the use of different bio-monitors like blue mussels is essential for the ability to verify the actual biological effect of various pollutions in the environment. During conditions like this, biological monitoring programs will be of high importance as a background reference in an effect evaluation.