What is the impact of ‘liming” lakes on the abundance and diversity of lake biota? (systematic review)
Background
Liming, adding of limestone or dolomite, has been conducted for many years in order to mitigate the acidification of lakes caused by ‘acid rain’. However, despite the longterm application of liming in many countries, there is still debate on the impact of liming on lake biota. Hence, we conducted a systematic review and meta-analysis in order to answer the question: What is the impact of ‘liming’ lakes on the abundance and diversity of lake biota?
Methods
A systematic search was conducted for all relevant papers using search terms for liming combined with terms for lakes and the biota. All articles found were included if they report on a study containing a relevant population (the biota in freshwater lakes), intervention (liming), and outcome (change in abundance/density or richness/diversity of biota).
Results
The search found 143 relevant articles. The available evidence suggests that on average liming increases the diversity of fish, zooplankton and phytoplankton, whereas the diversity of benthic organisms is not increased. The diversity of zooplankton and phytoplankton is estimated to decrease in some lakes but only in a small minority. The meta-analysis on the abundance of zooplankton, phytoplankton, and benthic invertebrates indicates they do not increase with liming. The impact of liming on fish abundance is less clear cut. The largest fish study suggests fish may increase in abundance with liming. However, there is a lack of studies with both baseline and control sites, making it hard to be certain whether the changes observed were due to liming. Liming has also been used to restore fish abundances by providing conditions for survival of stocked fish. The liming appears to have enabled the restocking of fish in some instances. However, many studies did not actually test if fish would have survived before liming or stock fish in control sites.
Conclusions
Increasing and preserving the diversity of organisms present in an ecosystem can (but may not always) represent a favourable ecological outcome, especially if achieved across a broad spectrum of the ecosystem and of acid sensitive species that were previously absent due to acidification. In this regard liming of lakes can be considered, in some circumstances, an effective conservation measure. However, in a minority of lakes diversity decreased with liming. The evidence base is insufficient to explore reasons for variation in effectiveness and more powerful study designs are required to enable prediction of when extremes of impact may occur.
Keywords
Liming, lakes, biota, zooplankton, phytoplankton, benthic organisms, macrophytes, fish
Background
“Acid rain” and the associated acidification of waterways first became a widespread environmental concern in the 1970‟s (Menz and Seip 2004). Since the industrial revolution humans have been releasing sulphur and nitrogen oxides into the atmosphere from industrial emissions, causing a decrease in the pH of rainfall in many areas, and hence of associated water bodies.
Acidification frequently causes changes in freshwater ecosystems including in the fish and invertebrates (Schindler et al 1985, Moiseenko 2005). In order to mitigate the problems of „acid rain‟, including acidification of water bodies, considerable efforts have been made to reduce industrial emissions since the 1980‟s. The emissions of sulphur have been successfully reduced through various legislations, both in Europe and North America, reducing the acidity of rainfall (Evans et al 2001). However, recovery is not uniform, there are still areas where the acid load outstrips the soils neutralizing capacity, nitrate emissions have not decreased to the same extent as sulphate emissions and the recovery of areas with decreased deposition is not uniform. Thus, there are still many areas that suffer from acidic surface waters and it may be many years before all surface waters recover, if ever (Evans et al 2001).
In order to protect lakes and fish stocks until the emissions can be reduced other methods have had to be implemented. One of the most widespread mitigation techniques is adding of calcium carbonate (lime) in order to raise the pH (Henrikson and Brodin 1995, Clair and Hindar 2005). Liming has been implemented in North America and many European countries but the largest liming programs are in Norway and Sweden. Sweden has invested 3.8 billion SEK (approximately €0.4 billion) on liming between 1983 and 2006 (Bostedt et al 2010).
Several studies have shown liming to increase salmon and trout stocks (ref), however there has previously been on systematic review of the impact and the impact of liming on other biota is more uncertain. Therefore this systematic review aims to find and summarise the best available evidence on the impact of liming on invertebrates, fish, diatoms and macrophytes (a sister review, CEE-09-015, is being conducted on river and streams; the reviews were divided as different parts of an ecosystem may react differently to liming). In conducting this review the impact of different liming techniques will also be investigated.