Long-term evaluation of potential Al toxicity after an Al treatment in a coastal bay

Coastal areas often suffer from eutrophication, causing ecosystem degradation and oxygen deficiencies. In hundreds of lakes, aluminium (Al) treatment has been a successful method to bind phosphorous in the sediments, reducing lake productivity. In this study we follow up a successful Al treatment of the sediment of Björnöfjärden, which was the first full-scale coastal remediation project using a geo-engineering method, that substantially reduced P concentrations in the water column. We evaluate the long-term development of Al in the water and aquatic life using 10 years data from before, during and after the aluminium treatment. Still after ten years, the treatment is successful with low P concentrations in the Bay. After a temporal increase of Al in water and biota (fish and algae) in connection with the Al treatment, the concentration decreased rapidly to pre-treatment levels. A risk assessment for biota and humans consuming fish and water from the bay showed that the risk for negative effects were negligible, also during the treatment year.