Dead fish in lakes and streams

Brit Lisa Skjelkvåle, University of Oslo

One of the main visible effects of acid rain is fish death in lakes and rivers. The observation of reduced catch of fish in lakes and rivers and occasional massive fish kills puzzled anglers and landowners already in the late 18th century. Many different hypothesis were discussed, and in the 1920’ies some fish hatcheries recognized that adding lime to the intake water reduced problems with fish death.

Still many decades went on before the link between acidified water and air pollution was established. With Svante Odens article in Dagens Nyheter in 1967, this link was officially established. In the 1970’ies there were a strong and impressive research activity were many of the fundamental processes related to acidification were established such as the concept of mobile anion to explain why acid rain could give acidic waters in spite of the buffer capacity in soils, and the discovery of Al as the main reason for fish kills.

The extent of acidified rivers and lakes and the extent of areas with dad and decreased fish stocks were mapped, monitoring programs started in many countries and the first mathematical models were developed. The joint international effort through UNECE to coordinate scientific findings on effects of air pollution on ecosystems and materials started in the 80ies, and we got the first S-protocol in this decade. The Norwegian RAIN-project documented the important result that runoff water would recover if S were reduced in deposition.

In the 1990`s, the water quality really started to recover. From now on the discussions was mostly related to how good it could get, how fast, and what about the recovery of the biota which was far slower and not so clear as the chemical recovery? Acid Rain had become a success story. But even if everything are moving in a right direction, there is still a way to go before we have healthy aquatic ecosystems not affected negatively by any air pollution.

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