Stable sulfur isotope analysis of SO₂ pollution impact on vegetation

The δ³⁴S value of SO₂ emitted by natural gas refineries is about +25, which is higher than that for non-industrial sulfur sources in our study areas. Terrestrial mosses absorb SO₂ from the atmosphere and have a δ³⁴S value which is directly related to the degree of SO₂ stress to which they are subjected. The δ³⁴S values for conifer needles are lower than for mosses at the same collection site, which indicates that trees obtain sulfur from both atmospheric and soil sources.Potted conifers were transferred to sites differing in their degree of SO₂ stress. This difference is reflected by the change of δ³⁴S values of their needles. SO₂ absorbant pot covers, such as charcoal and moss, reduce the amount of airborne sulfur which is available to tress. Moss also may reduce SO₂ absorbed by soils in forest stands. We have used analysis of δ³⁴S values to (1) help define SO₂ dispersion patterns; (2) reveal the rates at which plants accumulate this pollutant; and (3) associate suspected SO₂ injury more closely to an emission source.