Sulfate Fertilization and Changes in Stable Sulfur Isotopic Compositions of Lake Sediments

Abstract

Stable isotopes can record the origins and fates of anthropogenic pollutant sulfur in three ways. First, if pollutant sulfur has a distinctive isotopic composition, deposition and mixing of this sulfur will change isotopic compositions of natural waters and soils (Nriagu and Coker 1978; Krouse 1980). Unfortunately, isotopic compositions of pollutant sulfur are often similar to those present in the environment so that isotopic changes are small and accurate tracing of sulfur plumes is difficult. A second, more subtle effect involves isotopic changes that occur during metabolic adjustment to stress. For example, release of ³⁴S-depleted hydrogen sulfide by plants can be induced by high sulfur loading (Winner et al. 1981) with the result that residual plant sulfur becomes enriched in ³⁴S. Such stress effects may be common but are likely small and demand comparison to rigorously chosen controls. A third effect can be thought of as sulfur fertilization. Simply increasing the concentration of sulfur in the environment can lead to marked changes in isotopic compositions if processes are stimulated that result in isotopic fractionation. This review summarizes studies of sulfur storage in lake sediments, focusing on how increased sulfate deposition from the atmosphere alters natural isotopic compositions due to a sulfur fertilization effect.