IMPROVEMENTS IN BROWN TROUT AND INVERTEBRATE POPULATIONS IN THE ARKANSAS RIVER DURING RECLAMATION EFFORTS ON CALIFORNIA GULCH

Aquatic biological data have been collected from the upper Arkansas River since 1994 to monitor aquatic biological conditions in the river relative to historic mining and recent remediation activities in the California Gulch drainage. California Gulch flows directly into the Arkansas River and has historically contained elevated levels of several metals. Reclamation efforts (capping of waste rock piles, interception and treatment of adit water, etc.) have eliminated surge flows from the adits and lowered concentrations of metals entering the Arkansas River. Monitoring of brown trout populations has shown increasing trends in both density and biomass since 1994. Brown trout density and biomass were historically low downstream of California Gulch. However, trout density and biomass have been comparable or better than the reference condition upstream of California Gulch since 2002. Numbers of young-of-year brown trout have also improved. For macroinvertebrates, density, total number of taxa, number of mayfly taxa, and number of metal intolerant taxa have shown increasing trends downstream of California Gulch since 1994. The percent of total density as heptageniid mayflies is still somewhat lower than the reference sites, indicating some residual effects of California Gulch are still occurring. These data indicate reclamation efforts have improved conditions for the aquatic biota in the Arkansas River downstream of California Gulch. Additional