Sulfur impacts on forest health in west-central Alberta

The processing of sour natural gas results in the emission of sulfur dioxide (502) and elemental sulfur (50). An assessment was carried out in 1991 to compare soil and foliar chemical properties originally measured in 1981 and 1985 in forests near two sour gas processing plants in west-central Alberta. This study was expanded to evaluate forest health and tree growth in relation to sulfur (5) deposition in mature and immature lodgepole pine (Pinus contorta Doug!. vaL latifolia Engelm.) and mature trembling aspen (Populus tremuloides Michx.). Ten (50 x2 m) plots were established in 30 mature lodgepole pine sites, in 6 young lodgepole pine sites, and in 3 trembling aspen·dominated sites. The mature pine sites were classified into 3 deposition classes: high, medium, and low. The distribution of measurable So deposition increased from 2 km to 4-6 km from the SO load-out areas; however, SO concentration in the LFH near the gas plants has decreased since 1981. The medium deposition class sites had 5 concentrations in the LFH and foliage 6-20% higher than the low deposition class sites. Calcium (Ca) and magnesium (Mg) concentra· tions and pH were about 10% less in the medium deposition class sites than in the low depOSition class sites. It was, however, not possible to determine a cause and effect relationship between higher 5 in these sites and lower pH, Ca and Mg. A greater proportion of recently dead trees was found in high deposition class sites, but no difference was seen between the other two deposition classes. There was no increase in insectand disease-caused damage with increased 5 depOSition in the pine stands. Trembling aspen appeared to be affected by SO depOSition with in­ creased proportions of dead and declining trees and increased incidences of Armil· laria root rot and Hypoxylon canker in SO·dusted areas. There were no differences among depOSition classes on radial increments at dbh. Armual volume increments were depressed in high SO deposition sites; however, speCific volume increment was depressed in both the medium and high deposition classes indicating a possible physiological impact historically. Elevated 5 concentrations in the LFH and foliage and a depression in the annual volume increments were the only indicators of 5 impacts in lodgepole pine forests near the two sour gas processing plants. There was no apparent widespread forest decline outside of areas dusted with so.