The effect of short-term acidification during spring snovvmelt on selected Mollusca in south-central Ontario

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Abstract
Limestone and sulfuric acid were used to manipulate the pH of water in three artificial channels in the outflow of Plastic Lake, south-central Ontario, during the spring of 1982. Using artificial channels allowed the manipulation of pH during a natural pH depression (i.e., spring snowmelt) while minimizing confounding factors such as mobilization of metals from aquatic sediments. Addition of sulfuric acid extended and exaggerated the natural pH depression (from pH 5.8 to 4.8) to as low as pH 3.5 over 5 days, while addition of limestone prevented depression of pH below 6.4. Survival and reproduction of the pisidiid clams Pisidium equilaterale Prime and Pisidium casertanum (Poli) and the hydrobiid snail Amnicola limosa Say held in artificial channels were not significantly different (p > 0.05) among treatments. The survival and reproduction of A. limosa was also not affected by exposure to short-term pH depressions (e.g., 5.8 to 4.8; 4.8 to 4.3) in three south-central Ontario streams during spring snowmelt. For various life stages of both P. equilaterale and A. limosa, 96-h LC50 values were below pH 4.0, which was well below the pH observed in any stream in this study. These results suggest that recruitment failure and elimination of A. limosa from acidifying lakes noted in other studies was not a direct result of short-term pH depression during snowmelt.