Sulfate - Understanding Lake Data

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Sulfate in lake water is primarily related to the types of minerals found in the watershed and to acid rain. Industries and utilities that burn coal release sulfur compounds into the atmosphere that are carried into lakes by rainfall. In Wisconsin, the highest lake sulfate levels are found in the southeast portion of the state (Figure 8), where mineral sources and acid rain are more common.

FIGURE 8. Generalized distribution gradients of sulfate in the surface waters of Wisconsin lakes. (Adapted from Lillie and Mason, 1983(Exit DNR).

Map of Wisconsin showing how sulfate concentration changes

In water depleted of oxygen (anaerobic water), sulfate can be reduced to hydrogen sulfide (H2S). Hydrogen sulfide gas smells like rotten eggs and is toxic to aquatic organisms.

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The sulfide ion (S--) produced under these conditions can also affect the amount of metal ions in the lake since most metals, including iron and mercury, form insoluble sulfide precipitates. As a result of the high sulfate content (Figure 8), iron often exists in lower concentrations in southern lakes because it precipitates and settles out in sediments as iron sulfide.

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For more information on this topic, contact:

James Vennie
Watershed Management
(608) 266-2212


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Last Revised: Thursday January 25 2007