MERCURY ACCUMULATION IN DEVILS LAKE, NORTH DAKOTA – EFFECTS OF ENVIRONMENTAL VARIATION IN CLOSED-BASIN LAKES ON MERCURY CHRONOLOGIES

Sediment cores were collected from lakes in the Devils Lake Basin in North Dakota to determine if mercury (Hg) accumulation chronologies from sediment-core data are good indicators of variations in Hg accumulation rates in saline lakes. Sediment cores from Creel Bay and Main Bay, Devils Lake were selected for detailed analysis and interpretation. The maximum Hg concentration in the Creel Bay core was 0.15 micrograms per gram at 8 to 9 centimeters. The maximum Hg concentration in the Main Bay core was 0.07 micrograms per gram at 5 to 7 centimeters. The general decreases in Hg concentrations with depth are attributed to historic variations in atmospheric Hg deposition rate. Hg stratigraphies combined with210 Pb and 137Cs dating analyses yield Hg chronologies that indicate a general increase in Hg accumulation rates in Devils Lake since the middle of the 19th century.