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Abstract
Outflows from two atmospherically acidified lakes in the Bohemian Forest were studied in 2005 and 2007. While Lake Čertovo has been strongly acidified (∼pH 4.6), Lake Laka was only slightly acidified in the past and is recovering now (∼pH 5.2). The water chemistry and macrozoobenthos composition were analysed along longitudinal gradients of both lake outflows to determine the present status of their streams. A certain progression in stream chemistry to more neutral conditions was observed along the longitudinal gradients of both streams. However, a possible recovery of macrozoobenthos was evident only in the Lake Laka outflow, mainly via an increasing number of Ephemeroptera and Trichoptera taxa, and an increasing number of Gammarus fossarum, both along the longitudinal gradient and during the period of study. In contrast, no considerable changes were observed in the macrozoobenthos composition of the Lake Čertovo outflow, presumably because its chemistry was harmful for acidosensitive taxa such as Ephemeroptera and Trichoptera. Plecoptera and Chironomidae were the most numerous groups in this stream. The biological recovery of both streams will depend on further chemical improvement in their catchments as well as on the dispersal ability of benthic organisms.
Acknowledgements
This study was partly supported by the following projects: CSF 206/07/1200, MSM 6007665801, GAJU 143/2010/P and AVZ60170517. We wish to express our gratitude to Pavel Chvojka, Peter Bitušík, Tomáš Soldán, Jindřiška Bojková, Michal Straka, Vendula Křoupalová, and Petr Pařil for help with the determination of benthic macroinvertebrates, and to chemists at the Institute of Hydrobiology for their analyses.