ANTHROPOGENIC INVENTORIES AND HISTORICAL AND PRESENT ACCUMULATION RATES OF COPPER IN GREAT-LAKES SEDIMENTS

Sediment cores were collected from depositional basins in lakes Michig an, Ontario and Superior to assess spatial and temporal variations in Cu accumulation rates and inventories. Sediment chronologies were dete rmined via Pb-210 dating. and Pb-210 inventories were used to correct for the effects of sediment focusing. Among the lakes studied, Cu load ing histories generally decrease to the present, signifying a regional reduction in the anthropogenic release of Cu to the environment. Focu sing-corrected Cu accumulation rates in surficial sediments vary signi ficantly within lakes Michigan and Ontario, suggesting that recent inp uts of Cu to these 2 lakes may have been dominated by localized source s. Variations in Cu accumulation rates within Lake Superior are interp reted to be insignificant, suggesting either that Lake Superior is wel l-mixed with respect to copper inputs or that the lake is dominated by a single source for Cu. Recent measurements of atmospheric fluxes of Cu within the Great Lakes region generally indicate that the atmospher e accounts for less than 50% of the Cu accumulating in surficial sedim ents. Historical Cu accumulation rates from Lake Superior are poorly c orrelated with Cu production associated with local smelters, but agree favorably with national production rates. Trends in historical Cu acc umulation rates within all 3 lakes may indicate that recent declines i n Cu loading can be attributed to the enactment of stricter environmen tal regulations as well as changes in the use of Cu. Focusing-correcte d Cu inventories in lakes Michigan, Ontario, and Superior are generall y invariant within a given lake, indicating that, historically, these lakes have been dominated either by a single source or were well-mixed with respect to Cu inputs. The disparity between the results from rec ent accumulation rates and historical inventories may reflect differen ces in how the Great Lakes respond to contaminant loading on short (e. g. years) versus long (e.g. decades) timescales. (C) 1998 Elsevier Sci ence Ltd. All rights reserved.