Chemical, biological and socio-economic approaches to the liming of Lake Alinenj�rvi in southern Finland

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The aim of this comprehensive study is to estimate the effects and usefulness of liming Lake Alinenjarvi based on chemical, biological and socio-economic studies. Methodological standpoints concerning the limestone dissolution rate, acidic surges and reacidification are also discussed. L. Alinenjarvi (0.4S km2) is located near the city of Nokia with a surrounding population of over 5 000 (< 2 km). Before liming, the lake had only a sparse crayfish (Astacus astacus L.) population left, because reproduction had been failing since the early 1980s. The most important effect of liming is that it should connect with the potential production of crayfish. The roach (Rutilus rutilus L.) population was also affected. The liming improved the chemical quality of the water, and decreased also the Al and Mn concentrations. The number of phytoplankton species increased, and the species composition of periphyton changed after liming. The a-chlorophyll concentration in water remained low. Furthermore, crustacean zooplankton and benthic animals increased in abundance in the first late summer after liming. The diet analysis of perch (Perca fluviatilis L.) gave comparable results suggesting a possible positive effect of liming on their food resources. The improved water quality seems to make the reproduction of the crayfish possible again, but recovery would take several years. To guarantee a recovery, the introduction of new crayfish individuals and supplementary neutralizing methods would be needed. The results of a mailed survey showed that L, Alinenjarvi is a valuable water source for the local people. The most usual forms of leisure around the lake and shores are, however, outdoor recreation and swimming, with only minor usage for fishing. Despite that, though the immediate benefits would be negligible, a majority of local residents supported the continuation of liming even though they would have to carry the costs in the future.