Trends in Mercury Accumulation in Lake Sediments across the Upper Midwest, U.S.A

摘要

Statistically significant west-east trends of increasing surficial Hg concentrations and enrichment factors (EF) were found in sediments from 20 lakes across a 600 km transect in the Upper Midwest region of the United States. Location along the transect explained 21 percent of the variability in maximum surficial concentrations and 15 percent of the variability in sediment EF; there was no west-east trend in Hg concentrations for pre-industrial sediments. The average Fig enrichment factor in the eastern subregion was approx 1.0 greater than in the western subregion (an increase of-50 percent). Fig enrichment in the sediments decreased on average by approx 25 percent in the last 40 years, but the regional nature of enrichment has remained relatively constant. The results support the conclusion that atmospheric Hg deposition in this region is influenced by both continental or hemispheric-scale transport and regional-scale transport.