The Effects of pH on Lake Water Chemistry and Phytoplankton in a LaCloche Mountain Lake

Abstract

Abstract Some LaCloche Mountain Lakes and other soft water Shield lakes in the vicinity of Killarney Provincial Park (some 50–310 km south west of Sudbury, Ontario) have for the last decade been the subject of research on lake acidification. Acid precipitation (mainly from sulphur oxides) and lake waters of low buffering capacity apparently compound the problem. Typical pH values for such lakes range from 6.0–6.5, but pH values over the range 3.8–5.0 are not now uncommon. Loss of fish populations especially as a result of reproductive failure and changes in Zooplankton species composition have accompanied the lowering of pH which has occurred rapidly over the last two decades. The present study was on Carlyle Lake (Killarney Provincial Park) during the spring, summer, fall and winter of 1974–75. The pH values of water in cylinders floating in the lake were maintained at 4.0, 5.0, 6.0 and 6.5 respectively, for periods of six weeks, by additions of sulphuric acid or sodium hydroxide. Phytoplankton biomass was estimated by utermöhl technique, species identified and quantified at regular intervals during experiments. Maximum algal biomass in the cylinders occurred at pH 5.0 (close to the present pH of the lake). All major taxa had biomass maxima close to pH 5.0, with the exception of Cryptomonas ovata Ehrenberg, Chroomonas caudata Geit and Peridinium limbatum (Stokes) Lemm. which had maxima at pH 4.0. A preliminary comparison between the species composition and diversity of phytoplankton populations in LaCloche Lakes and in recently acidified lakes in similar geological rock basins in Western Europe is made.