Article ID Journal Published Year Pages File Type
4434129 Science of The Total Environment 2006 10 Pages PDF
Abstract

The outlet from the limestone treated Lake Terjevann consisted mainly of well-mixed lake water (mean pH 6.1) during the ice-free seasons including the unusually warm winters of 1992 and 1993. However, during the ice-covered period acidic water (mean pH 4.8, mean inorganic aluminium (Ali) about 160 μg/l) from the catchment draining under the lake ice dominated. A downstream tributary was generally acid and rich in aluminium (mean pH 4.6, Ali about 230 μg/l). After an extreme rainstorm loaded with sea-salts cation exchange in the soil resulted in more than a doubling of the Ali concentration (reaching about 500 μg/l). It took 3–4 months until the Ali concentration returned to pre-event levels. During the ice-covered period, the acidic outlet and tributary waters resulted in acidic conditions below the confluence (pH < 4.8, Ali about 150 μg/l) while during the ice-free periods the more neutral outlet water resulted in higher pH and lower Ali concentrations (pH > 5.2, Ali about 95 μg/l). However, during the latter climatic conditions the water was most probably more harmful to fish due to hydrolysing and polymerizing aluminium. After the sea-salt event, the increased Ali concentration in the tributary made the zone below the confluence potentially more toxic (pH ∼ 5, Ali ∼ 250 μg/l). Expected global warming resulting in winter mean temperatures above 0 °C may eliminate the seasonal acidification of the outlet from limestone-treated lakes creating permanent toxic mixing zones in the confluence below acidic aluminium-rich tributaries. Besides, more frequent rainstorms as a consequence of global warming may increase the frequency of sea-salt events and the Ali concentrations in the mixing zones.

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