Estimation of Temporal Acidification of Central Ontario Lakes

Abstract

The Wright–Henriksen model was used to estimate chemical changes in 255 central Ontario lakes attributable to strong acid loading. Background SO42− in precipitation, 14.5 μeq∙L−1, was estimated by analysis of "clean" events in contemporary data and used to determine background SO42− in lakes, which averaged 26 μeq∙L−1. Net (excess) SO42− averaged approximately 100 μeq∙L−1. An empirical function was used to calculate ANC0 (at historical t0) and ANC loss from net SO42−. Then, pH0 was estimated from ANC0, obtained with empirical and theoretical relationships of contemporary pHc and ANCc. Almost all of ANC0 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 ANC0 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 ANC0 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.