Mobilization of aluminium and deposition on fish gills during sea salt episodes - catchment liming as countermeasure

Summary

Episodic events may be critical with respect to aluminium(Al) toxicity in moderately acidified salmon rivers. The present work demonstrates that sea salt episodes enhance the toxicity of Al in acid rivers. The documented sea salt episode (10 mg Cl L-1) mobilized positively charged Al-species (10 to 30 µg Ali L-1), enhanced the Al accumulation on fish gills (25to 294 µg g-1 d.w.) and caused increased stress responses (6to15 mmol L-1 blood glucose) in fish. Accumulated Al on gills remained high several days after the episode. The presented results are based on a six-week field study in two tributary rivers on the west coast of Norway. Changes in the riverwater qualities and Al speciation were followed using in situ fractionation techniques. Al accumulation on gills and stressresponses were followed for Atlantic salmon (Salmo salar) kept in tanks continually exposed to the changing water quality. The potential mobilization of Al from the two catchments was studied by extracting soils with diluted seawater (3 ? salinity). To counteract Al toxicity, one of the tributary catchments has been limed. The potential mobility of Al by seasalt was lower in limed soils compared to acid soils, and the Al deposition on fish gills (<100 µg g-1 d.w.) and associated stress responses stayed low during the sea salt episode intheriver draining the limed catchment. Thus, for acid riversystems in coastal areas, catchment liming should be considered as a useful countermeasure for Al toxicity.