What is the aim of the review?

“Acid rain” and the associated acidification of waterways first became a widespread environmental concern in the 1970’s (Menz and Seip 2004). In the aquatic environment, acidification of waterways frequently causes changes in ecosystems including a reduction in fish and invertebrate numbers and diversity (Schindler et al 1985, Moiseenko 2005).  Acidification has had a particularly large impact on salmon populations.

In order to mitigate the problems of ‘acid rain’, including acidification of waterways, considerable efforts have been made to reduce industrial emissions since the 1980’s. Despite the reductions in emissions, biological recovery has been variable (Ormerod and Durance 2009) and acid episodes may be restricting biological recovery (Kowalik et al 2007). As removing the cause of acidification by reducing emissions has not always allowed full recovery and taken time to implement, symptomatic mitigation strategies have also been used.  One of the most widespread mitigation techniques is the addition of calcium carbonate (lime) to a watercourse (Clair and Hindar 2005).

There are still uncertainties about the effects on fish and invertebrates. For the first time, this systematic review summarises the best available evidence on the effectiveness of liming in restoring invertebrates and fish in rivers.