Publication

Summary

A mesocosm-experiment has been conducted with mine tailings from Titania A / S. The experiment has been part of the NYKOS project (New Knowledge of Sea Discharge), where NIVA received additional funds from Titania to process soft-bottom fauna and evaluate the effects. Addition of 2 cm tailings from Titania resulted in a significant reduction in the density of soft bottom fauna, and at the end of the experiment, the Titania boxes had <25% of the number of individuals compared to control sediments without added material. Also number of species was reduced. Previous experiments with addition of similar amounts of natural sediment material (sand and clay) have not had a significant effect on the soft bottom fauna, indicating that other factors than the hypersedimentation are responsible for the effects. In the Titania treatment, there were high concentrations the metals copper and nickel, corresponding to Class III-V (Norwegian Environment Agency report M-608), which indicates a risk of toxic effect. Furthermore, the nutrient value for the fauna was reduced, as shown by lower nitrogen and organic carbon content in the sediment. Lastly, it is possible that the particles physically harm the fauna as the crushing in the production process makes them more angular than ordinary sediment particles. The experimental setup is highly realistic as it enables controlled testing on intact bottom communities in its natural environment. At the same time, it is important to be aware that in contrary to a field situation, there is no recruitment of more tolerant species in the mesocosm. Thus, only mortality is measured. Furthermore, there is limited water exchange compared to the field situation. The effects are therefore intensified, and the results obtained in the present experiment are therefore considered to represent a worst-case scenario.