Whole-catchment application of dolomite to mitigate episodic acidification of streams induced by sea-salt deposition

To counteract mobilisation of potentially toxic aluminium (Al) ions to tributaries of salmon rivers, two paired-catchment experiments with terrestrial liming at two sites on the Norwegian west coast were performed. Streams at both sites experienced episodically elevated and potentially toxic Al levels induced by high deposition of sea salts. After application of 2 metric tons ha 1 of 0.2–2 mm dolomite powder at the Brommeland area, stream pH increased above critical levels at about pH=6.0 and remained stable throughout the monitoring period of 3.5 years. Inorganic aluminium decreased to below 20 Ag Al L 1, a water quality supposed to be nontoxic for salmon. This was evident also during extreme weather conditions with large relative increases in chloride (Cl) concentrations and negative calculated nonmarine sodium (Na*) concentrations in the streams, indicating potentially toxic sea-salt effects. Cl changed from being closely related to increases in inorganic Al, especially at the Brommeland stream (R2=0.75), to being not important (R2=0.12), but still significant for its variation. At the Hovland area, receiving 1 ton ha 1 of 0–2 mm dolomite powder, stream pH and Al effects were less clear-cut, probably due to the lower dolomite dose. Stream concentrations of both NO3 and SO4 2 increased significantly due to liming.