Comparative impacts of forest harvest and acid precipitation on soil and streamwater acidity

Abstract

Annual H + budgets were calculated for a catchment with a 65-year-old spruce-fir forest, and for an adjacent catchment at three years after a whole-tree harvest. In the harvested catchment sinks for H + due to weathering and mineralization reactions were 85% greater, and sources of H + due to biomass uptake were 60% greater than in the undisturbed catchment. There was an overall net consumption of 550 eq H + ha −1 year −1 at year 3 after harvest compared to a net generation of 520 eq H + ha −1 year −1 for the 65-year-old forest. Soil pH increased by 0·2–0·4 units soon after harvest, but there was little change in pH of streamwater from the harvested watershed. The whole-tree harvest resulted in a total production of about 30 000 eq H + ha −1 due to biomass removal. In contrast, wet and dry deposition at rates measured in this study could add more than 50 000 eq H + ha −1 in the 65-year period before the next harvest. Reducing the intensity of harvest may lessen long-term impacts of these sources of H + on acidification of soils and streams.