The rate of acidification of aquatic ecosystems in Ontario, Canada

Abstract

Although the acidification of lakes and streams in several parts of the world as a consequence of the emission and deposition of S and N oxides is well-documented^1–4, no direct measurement by continuous monitoring of acidification rate of any lake has been reported. In many cases, historical data have been compared to recent data and acidification of aquatic systems, generally over periods of decades, demonstrated. But methodological changes have always compromised the results. In other cases, historical chemical conditions of lakes and streams have been inferred from either geochemical relationships⁵ or from palaeolimnological records^6,7 and compared to current conditions. Here we present the first direct observations of the acidification rate of a lake that has undergone extensive damage to its aquatic biota as the result of deposition of acids of anthropogenic origin. A threefold decrease in alkalinity and a decrease of 0.2 pH units occurred in the lake despite a reduction in the deposition rate of strong acids over the period of study. Acidification was accompanied by a decrease in base cation content in the lake but not an increase in strong acid anion (SO^2–₄) concentration, indicating that there has probably been a depletion of available cations in the lake's catchment.