Mercury contamination of remote lakes has been attributed to increasing deposition of atmospheric mercury, yet historic deposition rates and inputs from terrestrial sources are essentially unknown. Sediments of seven headwater lakes in Minnesota and Wisconsin were used to reconstruct regional modern and preindustrial deposition rates of mercury. Whole-basin mercury fluxes, determined from lake-wide arrays of dated cores, indicate that the annual deposition of atmospheric mercury has increased from 3.7 to 12.5 micrograms per square meter since 1850 and that 25 percent of atmospheric mercury deposition to the terrestrial catchment is exported to the lake. The deposition increase is similar among sites, implying regional or global sources for the mercury entering these lakes.

The importance of the principal natural scavenging agents for hydroxyl radicals (•OH) was evaluated, and a general framework was developed to predict the significance of nitrate-induced, •OH-mediated degradation of aquatic contaminants. Rate constants for •OH scavenging by dissolved organic matter (DOM) from five surface water sources were in a narrow range (2.3 ± 0.77 × 104 (mg of C/L)-1 s-1), which is similar to previously reported values and suggests that the importance of DOM as a •OH sink can be estimated simply from the dissolved organic carbon (DOC) concentration of a water. Scavenging of •OH by carbonate and bicarbonate is generally less important, but these ions can be the major cause of •OH scavenging in low DOC, high alkalinity waters. Use of the framework is illustrated by predicting levels of •OH and half-lives of the corn herbicide acetochlor in waters ranging from pristine to highly influenced by agricultural activities.

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