Advancements in modeling mercury transport and fate in a dynamic fluvial system

摘要

The U.S. EPA designated the Carson River as part of a Superfund site in 1991 due to contamination by mercury. Liquid mercury was used in the amalgamation process to extract gold and silver from the Comstock Load during the later portion of the 19~(th) century. It is estimated that approximately 6.36 X 10~6 Kg (7,000 tons) of residual mercury is now distributed throughout the river's bank sediments and floodplain deposits (MILLEP, 1997; SMITH & TINGLEY, 1998). On average, these bank concentrations are very high (64,242 mu g/Kg). Water column total mercury concentrations are also extremely high. The U.S.G.S reports water column concentrations reaching 28,000 ng/L (HOFFMAN & TAYLOR, 1998). This concentration approaches toxicity levels that are 5 times greater than the U.S. EPA maximum concentration limit for freshwater systems (MILLS et al., 1985). It was also discovered that more than 95 percent of the mercury transported in the Carson River is affiliated with particulate matter (BONZONGO et al., 1996). Therefore, to understand mercury transport and fate it is necessary to accurately describe bank erosion and sediment transport processes.