The Impact of Simulated Acid Rain on Soil Leachate and Xylem Chemistry in a Jack Pine (Pinus Banksiana Lamb.) Stand in Northern Ontario, Canada

Abstract

The impact of simulated acid rain on soil leachate and xylem chemistry in a young Jack pine (Pinus banksiana Lamb.) stand in the boreal forest of northern Ontario was evaluated. Permanent plots (5 × 2 m) were established in 1981 which were sprayed twice monthly with simulated acid rain, adjusted to pH 5.6, 4.0, 3.5, 3.0 or 2.5 with a 2:1 molar ratio of sulphuric (H2SO4) to nitric acid (HNO3) in addition to ambient rainfall. Sprays were applied between June and September for 5 yr. Unsprayed plots were also monitored. The pH of soil leachate collected between 1981–1985 was reduced significantly by the acid sprays and concentrations of sulphate (SO42-), nitrate (NO3-), calcium (Ca), magnesium (Mg), aluminium (Al), manganese (Mn), and zinc (Zn) increased in the A, B and C horizons. The soil recovered rapidly from the spray treatments, although residual effects were found in soil leachate samples collected during 1986–1987, particularly in the C horizon. Trees receiving spray acidified to pH 2.5 had higher concentrations of Ca, Mn, Cd and Rb in tree-rings formed between 1981–1985 compared to trees receiving spray acidified to pH 4.0 or to trees receiving ambient rainfall alone. Some of the changes in soil chemistry resulting from the application of acidic sprays are reflected in the chemistry of Jack pine tree rings and these chemical signals in tree rings may be used as indicators of soil acidification.