Organic volatile sulfur in lakes of the Canadian Shield and its loss to the atmosphere

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Abstract
Identities, concentrations, and fluxes of volatile sulfur compounds (VSCs) were determined in 11 lakes in northwestern Ontario. Carbonyl sulfide (COS: up to 1.1 nM) and dimethyl sulfide (DMS: up to 11 nM) were present in surface waters during most of the ice‐free season. Depth profiles showed accumulations below the mixed layer of methane thiol (MSH), DMS, and dimethyl disulfide (DMDS). There was no effect of low pH or increased [SO42−] (from 2.4 to 12.3 mg liter−1) on the concentrations and identities of surface‐water VSCs. Accumulation of DMS below the mixed layer was 9 × higher in an acidified system, however, when compared to an unacidified reference lake. Estimates of flux from two stratified lakes indicated that volatilization was not an important sulfur loss mechanism compared to others such as sedimentary SO42 reduction.Concentrations of MSH, DMS, and DMDS in shallow Lakes 114 and 303 were often 5–30 × higher than in any other lake studied, and the flux from Lake 114 was ∼0.96–1.6 × the estimated oceanic DMS flux per unit of area. On a regional basis, in areas where SO42− in precipitation is low, export of VSCs to the atmosphere from shallow lakes and bog pools may be significant compared to sulfur inputs through precipitation.

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