Effects of Experimental Acidification on Phyto‐, Bacterio‐and Zooplankton in Enclosures of a Highly Humic Lake

In situ enclosure experiments were performed in a highly humic lake to examine the effects of acidification on phyto‐, bacterio‐ and zooplankton. The acidity of three enclosures was adjusted with H2SO4 to pH 3.5, 4 and 5 and one enclosure and the lake served as controls. The diversity of plankton as well as the mean concentration of chlorophyll α, primary production and respiration of plankton decreased with increasing acidity. Bacterial density was slightly lower in the pH 3.5 enclosure than in the other enclosures and in the lake, but there were no differences in the morphological type or mean volume of the cells between different treatments. In the acidified enclosures Cryptomonas ovata and Chlamydomonas spp. were the dominant phytoplankters, while Dinobryon and Mallomonas species seemed to be most sensitive to acidity. Keratella cochlearis, Kellicottia longispina and Bosmina longispina were the most tolerant zooplankton to acidity.