Nitrogen fluxes in a high elevation Colorado Rocky Mountain basin

Abstract

Measured, calculated and simulated values were combined to develop an annual nitrogen budget for Loch Vale Watershed (LVWS) in the Colorado Front Range. Nine-year average wet nitrogen deposition values were 1·6 ( s =0·36) kg NO 3 -N ha −1 , and 1·0 ( s =0·3) kg NH 4 -N ha −1 . Assuming dry nitrogen deposition to be half that of measured wet deposition, this high elevation watershed receives 3·9 kg N ha −1 . Although deposition values fluctuated with precipitation, measured stream nitrogen outputs were less variable. Of the total N input to the watershed (3·9 kg N ha −1 wet plus dry deposition), 49% of the total N input was immobilized. Stream losses were 2·0 kg N ha −1 (1125 kg measured dissolved inorganic N in 1992, 1–2 kg calculated dissolved organic N, plus an average of 203 kg algal N from the entire 660 ha watershed). Tundra and aquatic algae were the largest reservoirs for incoming N, at approximately 18% and 15% of the total 2574 kg N deposition, respectively. Rocky areas and forest stored the remaining 11% and 5%, respectively. Fully 80% of N losses from the watershed came from the 68% of LVWS that is alpine. © 1997 John Wiley & Sons, Ltd.