Effects of a rainstorm high in sea-salts on labile inorganic aluminium in drainage from the acidified catchments of Lake Terjevann, southernmost Norway

The acidification of many streams and lakes that has occurred in southern Norway during several decades is to a large extent caused by acid deposition. However, in coastal areas deposition events with high loading of sea-salts may result in increased acidity and aluminium concentration in the discharge. Since such episodes are difficult to predict and usually of short duration, the aluminium chemistry during such episodes has so far not been evaluated in detail. In January 1993, during monitoring of streams in the Lake Terjevann catchment, the area was exposed to an extraordinary high sea-salt loading. The Cl- concentration in the stream water more than doubled (reaching about 900 mu eq/l), the labile inorganic aluminium (Ali) concentration almost quadrupled (reaching about 33 and 18 mu M in the two streams), and the relative increase in the Al3+ concentration was even higher. It took 3-4 months until the Al-i concentration and almost a year until the Cl- concentration returned to pre-event levels. Simple equilibria with minerals such as gibbsite, jurbanite, kaolinite/halloysite or imogolite do not control aluminium concentration in the discharge from these catchments. Retention of Na+ more than compensated for the desorption of Al3+. The results strongly indicate that cation exchange in the organic soil layers was essential in controlling the aluminium chemistry in the stream waters especially during high flow. Similar, but less pronounced, effects of the sea-salt episode were seen at the Birkenes catchment about 37 km inland from Lake Terjevann. (C) 1999 Elsevier Science B.V. All rights reserved.