Neutralization and Fertilization of Acidified Lakes Near Sudbury, Ontario

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Abstract
Investigations into the consequences of neutralizing acidic lakes, establishing buffer systems and reducing heavy metal levels by additions of Ca(OH)2 and CaCO3 are described. Two pairs of lakes in the immediate vicinity of Sudbury, Ontario, were chosen for study commencing in June 1973. Prior to treatment, all lakes could be described as soft (hardness 21–47 mg/l as CaCO3), poorly buffered (alkalinity 0.4–2.6 mg/l as CaCO3) with low pH values (4.4–4.5). Sulphate was the dominant ionic constituent in the lakes (26–55 mg/l). Copper and nickel levels were among the highest recorded in the Sudbury region. The low HPC: aciduric ratio (total heterotrophic plate count: acid-tolerant plate count) demonstrates the atypical bacterial composition of the lake waters. The standing stocks of phytoplankton, Zooplankton and zoobenthos were somewhat lower and taxonomic composition abnormal as compared to “typical” oligotrophic lakes on the Canadian Shield as studied in the Experimental Lakes Area of Ontario. The two downstream lakes were treated in the fall of 1973, one with Ca(OH)2 only; the other with a combination of Ca(OH)2 and CaCO3. The upstream lakes were monitored as controls. Both treated lakes showed an increase in pH to about 7.0 and reductions in total Cu, Ni and Zn levels of 13–83%. The combination treatment proved superior in that a more stable buffer system was established and pH remained near neutrality for the duration of the study. The rapid pH change (three units in a matter of weeks) caused an initial decline in the standing stock of phytoplankton, Zooplankton and zoobenthos. The bacteria were the first to show a positive response to the altered water chemistry; the HPC: aciduric ratio increasing immediately following treatment. The phytoplanktonic standing stock increased and the taxonomic composition changed the summer following treatment. Numbers of Zooplankton and zoobenthos did not increase the year following treatment, probably because of the relative difficulty in recolonization and their slower reproductive rate. In an effort to increase biological standing stock, Middle Lake was fertilized with phosphorus 1½ years after neutralization. Numbers of phytoplankton and Zooplankton increased and taxonomic composition shifted.

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