Degree of acidity. Vennesla is exposed for much acid rain.The direction of the wind and much fall of rain combined with acid ground and a soil which does not buffer acid rain, have caused many empty fishing waters in the munucipality.The combination of low pH values anda large quantity of unstable aluminium in the water is fatal for the fishes. This situation has considerably damaged the population of trout in the south of Norway.Today we calculate that 70 per cent of the population of fish in the county is extinct while an 20 per cent is damaged. Acidity is measured in pH units. The lower the pH values are, the higher is the consentration of oxonium ions. In neutreal water pH is 7.0 whilethe pH value in pure rain is about 5,6. This is because of water in contact with air dissolves CO2 and the contents of carbonic acid lowers the pH values. Even though the outlet of NOx and especially SO2 has been reduced in later years, increased amount of rain has caused that the amount of sulphur in nature has not has been reduced as much as the reduction in outlet should signify. The total amount of sulphur and nitrogen is important for the extent of damage, while the pH values have not been reduced much.
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