Warmer air temperatures may explain increases in zinc and other metal concentrations of ecological concern in a Rocky Mountain watershed, a report says. Researchers at the University of Colorado at Boulder report temperature increases since the 1980s causing falling water tables, melting permafrost and accelerating mineral weathering rates have led to a fourfold increase in dissolved zinc in the upper Snake River just west of the Continental Divide near Keystone, Colo. Working in collaboration with the U.S. Geological Survey, researchers say there is concern over possible comparable increases in metals in similar Western watersheds that could have impacts on water resources, fisheries and stream ecosystems. Much of the metal making its way into watersheds is from acid rock drainage, or ARD, a natural process of weathering of pyrite and other metal-rich sulfide minerals in the bedrock, researches say. \"Acid rock drainage is a significant water quality problem facing much of the western United States,\" USGS research biologist Andrew Todd said. \"It is now clear that we need to better understand the relationship between climate and ARD as we consider the management of these watersheds moving forward.\" The problem is compounded by metal from past and current mining activities in a phenomenon known as acid mine drainage, or AMD, researchers said, and the study has important implications in mine cleanup efforts because it suggests establishing attainable cleanup objectives could be difficult if natural background metal concentrations from ARD are a \"moving target.\"