Acidification of lakes has large impacts on aquatic ecosystems, and even after chemical conditions improve, biological recovery may lag behind. A study of Swedish lakes shows that, although their chemical quality has improved as a result of international reductions in acidifying emissions since 1980, biological recovery has been much slower.
The researchers have specifically looked at the roach (Rutilus rutilus), a species of fish that is very sensitive to acidification and cannot reproduce at pH levels below 5.5. Historical records of roach in 85 Swedish lakes were used and compared with the chemical model MAGIC, and it was found that chemical recovery occurred in all the acidified lakes, but roach only return to some lakes, and then mostly after manual restocking.
“This shows both that chemical recovery is a prerequisite for biological recovery and that a greater emission reduction in turn leads to greater chances of biological recovery. Unfortunately it also shows that a chemical recovery does not guarantee that the fish automatically will return once the water reaches a decent level,” said Filip Moldan, researcher at IVL Swedish Environmental Research Institute.
Source: IVL news, 3 April 2014