Changes in climate and hydrochemical responses in a high‐elevation catchment in the Rocky Mountains, USA

Abstract

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 radiation for the summer months. The increase in precipitation amount explains about half of the 200% increase in annual wet deposition of NO 3‒ to Niwot Ridge over the last decade. Differences in climate parameters between 1994 and 1995 (increased snow depth and decreased net energy flux 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 the form of an ionic pulse is causing episodic acidification (ANC < 0 µ eq liter‒1) in headwater catchments at present deposition levels. Small changes in climate parameters may cause large changes in the hydrochemistry of alpine streams. The changes in climate at Niwot Ridge are not in synchrony with lowland warming in the Great Plains to the east and serve as a reminder that climate in alpine areas is driven by local conditions and may be asynchronous with regional and global climate trends.