Trace-element enrichment in streambed sediment and crayfish, Carson and Truckee rivers, Nevada and California, September 1992

Abstract

The Carson and Truckee River Basins in Nevada and California are part of the U.S. Geological Survey National Water-Quality Assessment Program. This program is designed to determine the status and trends of water quality in the United States. Concentrations of aluminum, arsenic, chromium, copper, lead, mercury, nickel, selenium, silver, vanadium, and zinc in streambed sediments and in samples of the western crayfish (Pacifastacus leniusculus) are summarized and compared. The samples were collected in September 1992 from 11 sites on the Carson and Truckee Rivers.Past mining and ore-milling practices have enriched the Carson River bed sediments and crayfish with several trace elements. Enriched concentrations of aluminum, arsenic, chromium, copper, lead, mercury, nickel, and selenium were measured in streambed sediment collected at the East Fork Carson River near Gardnerville, Nev. Possible sources of these trace elements include natural mineral deposits and areas affected by human activity. Mercury and silver were enriched in streambed sediment downstream from Carson City, Nev., as a result of historical ore milling during the Comstock era. Crayfish downstream from the East Fork Carson River near Gardnerville were moderately to highly enriched with aluminum, arsenic, mercury, and nickel. Arsenic concentrations were significantly higher in the Carson River bed-sediment samples than in the Truckee River bedsediment samples. Urban activity may be the primary source of trace-element enrichment in Truckee River bed-sediment and crayfish samples. However, agricultural activity, historical ore milling, and geothermal discharge also may contribute trace elements to the river. Bed sediment and crayfish from the Truckee River at Reno and downstream were enriched with arsenic, lead, mercury, and silver.Statistically significant relations were measured between arsenic, mercury, and silver concentrations in bed-sediment and crayfish samples from the Carson and Truckee Rivers. These relations indicate that arsenic, mercury, and silver were bioavailable and were bioaccumulated in crayfish, especially in the Carson River. _^_ ___ feasin and Range Study Unit. NatlorralWater-Qyality Assessment Program* Kick sampling for crayfish in the Truckee River at Lockwood,