Recovery from acidification in Nova Scotia: temporal trends and critical loads for 20 headwater lakes

The chemical response of 20 headwater lakes in Nova Scotia to reduced acid deposition was investigatedusing trend analysis, and the need for further reductions was assessed using two steady-state, critical load models.Significant decreases were observed in the concentration of nonmarine sulphate (SO42) and hydrogen (H+) at four wetdeposition monitoring stations across Atlantic Canada since 1984. Dominant trends in surface water were decreasingSO42 concentrations, with little improvement in alkalinity and H+. Based on the Steady State Water Chemistry(SSWC) and First-order Acidity Balance (FAB) models, and using a critical chemical limit for acid-neutralizing capacityof 20