Estimation of Temporal Acidification of Central Ontario Lakes

The Wright–Henriksen model was used to estimate chemical changes in 255 central Ontario lakes attributable to strong acid loading. Background SO 4 2− in precipitation, 14.5 μeq∙L −1 , was estimated by analysis of "clean" events in contemporary data and used to determine background SO 4 2− in lakes, which averaged 26 μeq∙L −1 . Net (excess) SO 4 2− averaged approximately 100 μeq∙L −1 . An empirical function was used to calculate ANC 0 (at historical t 0 ) and ANC loss from net SO 4 2− . Then, pH 0 was estimated from ANC 0 , obtained with empirical and theoretical relationships of contemporary pH c and ANC c . Almost all of ANC 0 of 125 μeq∙L −1 on average was lost in one group of lakes near Sudbury. Associated mean pH decrease was 0.8–1.4 depending on the model used. Approximately 60–70% of ANC 0 of 110 μeq∙L −1 was lost, with a pH decrease of 0.3–0.8, in lakes of two groups near Parry Sound. Only 20–30% of ANC 0 of 160 μeq∙L −1 had been lost, with little pH change, in a group of lakes closer to Sault Ste. Marie. Such estimates are required for a rational interpretation of data on the distribution of fish species in Ontario lakes and estimation of losses of fish.