Regional patterns of wet mercury deposition.

Most of the mercury contamination in lakes and streams of nonindustrialized regions of the United States and Canada is derived from atmospheric deposition. In order to determine the regional patterns of these inputs, seven mercury-in-precipitation monitoring sites were established in Minnesota, North Dakota, and Michigan. A 3-year study showed that the magnitude of mercury deposition was dominated by the quantity of precipitation. Regional variations of mercury concentrations in precipitation were mostly explained by precipitation rate with higher concentrations occurring in the summer. Statewide (Minnesota) annual mercury emission estimates exceeded depositions for 1990, 1991, and 1992 by a factor of approximately 2 and indicated long-range transport of mercury. Significant correlations were observed between concentrations of mercury and other ions in precipitation.