Lake Sediment Core Records of Sulphur Accumulation and Sulphur Isotopic Composition in Central Ontario, Canada Lakes

Stable isotopic compositions and concentrations of total sedimentary sulphur (S) were determined in coresfrom 6 lakes in the acid-sensitive Muskoka-Haliburton region of south-central Ontario. The isotopiccomposition of S in deep sediment (> 20 cm) was approximately constant in all lakes, and indicated a preindustriald34S value between +4.0 and +5.3&, which is similar to current bulk deposition. Similarly, totalS concentrations in deep sediment were relatively low (1.95 mg S g 1 dwt) and approximately constantwith depth within cores. All lakes exhibited up-core increases in total S and decreases in d34S at a depthcorresponding to the beginning of industrialization in the Great Lakes region ( 1900), resulting in agenerally reciprocal depth pattern between total S concentration and d34S ratios. While initial shifts in totalS and d34S were likely due to enhanced SO4 reduction of newly available anthropogenic SO4, both themagnitude and pattern of up-core S enrichment and shifts in d34S varied greatly among lakes, and did notmatch changes in S deposition post 1900. Differences between lakes in total S and d34S were not related toany single hydrologic (e.g., residence time) or physical (e.g., catchment-area-to-lake area ratio) lakecharacteristic. This work indicates that sediment cores do not provide consistent records of changes in postindustrialS deposition in this region, likely due to redox-related mobility of S in upper sediment.