A. Fjellheim et Gg. Raddum, Acidification and liming of River Vikedal, western Norway. A 20 year studyof responses in the benthic invertebrate fauna, WATER A S P, 130(1-4), 2001, pp. 1379-1384
This paper deals with benthic invertebrate population responses to acidific
ation and liming in the lower part of River Vikedal. In 1979 the river show
ed signs of increasing acidification. Highly sensitive invertebrates like t
he mayfly Baetis rhodani were present in the river in low abundance, but di
sappeared in the subsequent years. In order to re-establish a nontoxic wate
r quality for fish, liming of the spring snowmelt to a minimum of pH 5.7 wa
s started in 1987. During the later years liming has been successively incr
eased. The invertebrate fauna showed a slow, but positive, response during
the first years after liming, especially during autumn. B. rhodani recoloni
zed the river in low density, but the spring cohort was still weak. Since 1
994 the lime dosage was increased to secure a minimum pH of 6.3 during spri
ng snowmelt. This has resulted in an overall increased biodiversity in the
limed section of the river. Several acid-sensitive species, like both cohor
ts of B. rhodani and freshwater snails have colonized this part of the rive
r. Simultaneously biodiversity in the unlimed reference sites has slightly
improved during the last years. This is correlated with decreased sulphur d
eposition and improved surface water chemical conditions.