Recent Temporal Patterns in the Chemistry of Small, Acid-sensitive Lakes in Central Ontario, Canada

We monitored the chemistry of 603 small water bodies in three acid-sensitive regions of central Ontario, Canada (Algoma n=235, Muskoka n=216, Sudbury n=152) between 1988-1996 to determine whether they have responded to recent SO2 emission reductions, and whether any chemical changes were related to lake characteristics. During the study, 27-56% of lakes declined in SO42- concentrations, 41-57% declined in base cation concentrations, but only 26-28% increased in pH or ANC (acidity status). Increases in pH were greatest in lakes with low ANC, but had weak relationships to lake color or volume. No consistent trends were observed for DOC, NO3- or TP concentrations. Clearly, the long-term biological recovery of these sensitive aquatic ecosystems will depend on interactions among several environmental stressors, including acidification.