CHANGES IN CLIMATE AND HYDROCHEMICAL RESPONSES IN A HIGH-ELEVATION CATCHMENT IN THE ROCKY-MOUNTAINS, USA

A continuous climate record since 1951 at Niwot Ridge in the Colorado Front Range shows a decline in mean annual temperature, an increase in annual precipitation amount, and a decrease in mean daily solar radia tion for the summer months. The increase in precipitation amount expla ins about half of the 200% increase in annual wet deposition of NO3- t o Niwot Ridge over the last decade. Differences in climate parameters between 1994 and 1995 (increased snow depth and decreased net energy f lux to the snowpack) resulted in a 4-5-fold increase in the magnitude of solute release from the snowpack in the form of an ionic pulse. In turn, the high chemical loading of strong acid anions in the seasonal snowpack and release of these solutes from the seasonal snowpack in th e form of an ionic pulse is causing episodic acidification (ANC < 0 mu eq liter(-1)) in headwater catchments at present deposition levels. S mall changes in climate parameters may cause large changes in the hydr ochemistry of alpine streams. The changes in climate at Niwot Ridge ar e not in synchrony with lowland warming in the Great Plains to the eas t and serve as a reminder that climate in alpine areas is driven by lo cal conditions and may be asynchronous with regional and global climat e trends.