Liming in Ontario: Short-term biological and chemical changes

The short-term results of a 5-yr experimental lake neutralization program involving whole-lake liming of Trout and Bowland Lakes are reviewed. Whole-lake liming did not prevent spring melt pulses of acid and Al in a zone situated under the ice nearshore. Liming did improve whole-lake water quality in a previously acidified lake (Bowland Lake) so that lake trout (Salvelinus namaycush) could be restocked successfully. In situ bioassays showed a statistically significant improvement in survival of overwintering lake trout eggs after liming. Lake trout fry exposed during spring melt also showed increased survival rates after liming except at one site in Trout Lake where liming did not prevent the occurrence of 100% mortality. The resident yellow perch (Perca flavescens) population in Bowland Lake exhibited short-term increases in survival and in recruitment the first year following neutralization. Growth rate responses differed among age cohorts. A preliminary shoal liming experiment in Laundrie Lake suggested that nearshore spawning shoals which are not necessarily protected by whole-lake liming may be protected by treatment with fine calcite gravel.