Attempts to Reduce Effects of Acidification on Fishes in Norway by Different Mitigation Techniques

Abstract

In 1979, a five-year Norwegian Liming Project was initiated. This paper summarizes results relevant to fish obtained to date. Different stages of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta) have been used as test organisms. In hatcheries, shellsand filters and addition of seawater have proved successful. In spawning areas, dosing with lime slurry and mixing of shellsand into the spawning substrate enhanced survival. In running water, wells containing shellsand or limestone had only limited neutralizing capacity. Likewise, additions of powdered limestone to running waters had limited effects because of slow dissolution rates. Lime slurry, on the other hand, efficiently neutralized running waters and was easy to control. No toxic zones were found, even close to the liming site. In lakes, use of soda (Na2CO3) has great limitations, whereas experiments with slurry and powdered limestone were successful. Application of NaOH increased stress on smolts at pH levels slightly above 7, probably due to formation of aluminate ions. Use of alkalies containing divalent cations is preferred because of the protective effects of ions such as calcium.