Liming activities in Sweden have included extensive studies of fish fauna in lakes and running waters, with the result that it is now possible to make well-founded generalizations concerning the effects of treatment on this group of organisms. It is more difficult to make generalizations about lake zooplankton and benthic fauna, which have mainly been studied within the framework of research projects. Benthic faunas in running waters have almost exclusively been studied in conjunction with general monitoring of liming effects, via a large number of individual projects. Such projects have provided material to enable the effects to be described, but not the causal relationships. Little work has been done in this context on aquatic birds and only isolated studies have been performed on frogs.A succession of changes in the animal communities commences directly after liming, which means that the observed changes in fauna vary depending on how much time has elapsed since treatment. For species with short life cycles, such changes occur relatively rapidly. Communities continue to develop over long periods after liming; in some cases for at least fifteen years.Post-liming changes in fauna can be summarized as follows: species of fish, mayflies (Ephemeroptera), snails and zooplankton (e.g. waterfleas, Cladocera) which have died out as a result of acidification return and, in general, the number of species in these groups increases. The number of species of benthic fauna and pelagic insects may either increase, decrease or remain unchanged. One explanation in cases where the number of species does not increase is that certain acidophilic species such as non-biting midges (Chironomidae) and water boatmen (Corixidae) disappear or decline to densities which are too low to be measured in practice.Among fish and Zooplankton, both the density of individuals and the biomass increase in the long term, while inconsistent results have been observed among benthic fauna. Opportunistic species, i.e. species which may appear in dense populations over a short period after liming, are to be found among several groups of benthic faunas. The density of water fowl does not appear to change immediately after liming. The declining trend in the production of young osprey (Pandion haliaetus) has been halted in areas where extensive liming has been performed. Improvements in the growth and condition of individual fish have been observed, together with improvements in fish and Zooplankton reproduction and frog spawn survival.Detoxification of the water is the primary reason why species which are susceptible to acidification are able to re-establish and increase in density. Such abiotic changes are the result of liming and alter the biotic conditions, i.e. competition and predation, so that in the long term they determine how individual taxa and Community structure develop. For many species, the in- creased food supply is one important factor, while certain species may benefit from a short-term increase in the availability of a specific food resource.The main post-liming changes occur in lakes where acidification has had a far-reaching impact on communities of organisms. Thus, protective liming provides the best strategy to preserve susceptible faunas. If liming treatment is properly performed, the fauna develops as time goes on to attain a composition which largely resembles that which existed prior to acidification — it becomes normalized. It does not, however, recover to become identical to that which originally existed. Apart from biotic factors such as predation and competition, abiotic factors such as water quality, liming strategies and recolonization determine whether the faunal Community will develop to the extent that it can regain a more normal structure.Unstable water quality in conjunction with acid surges which result from an inflow of acidified and metal-rich water into lakes or from the break-down of dosers in running waters, for instance, may delay and obstruct such development, however. In the long run, the nutrient status of the lake is probably also of significance. The liming strategy is not crucial as long as the water quality is improved sufficiently to become reasonably stable. In certain cases, particularly in conjunction with liming of running waters, this has not been achieved and has meant that the fauna has not recovered as expected. A combination of different methods such as liming with dosers, wetland liming and liming of upstream lakes provides the best result in running waters. The possibility of local recolonization of extinct species depends on the capability of the individual species, how far from the limed water the species are to be found, and the existence of migration barriers and competition from established acidification-tolerant species. In order for locally extinct species to recover quickly, supplementary measures are sometimes required such as elimination of migration baniers.The overwhelming proportion of post-liming changes in fauna can be considered desirable and expected, seen in the context of the effects of acidification. Certain undesirable effects have been observed in conjunction with acid surges and metal precipitation, but these can usually be remedied by adapting the liming strategy accordingly.
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- The effects of liming on aquatic fauna
- Springer Berlin Heidelberg