In the Rocky Mountains, the association of increases in acidic deposition w
ith increased atmospheric loading of sulfate and direct changes in surface
water chemistry has been well established. The importance, though, of incre
ased nitrogen (N) deposition in the episodic acidification of alpine lakes
and N saturation in alpine ecosystems is only beginning to be documented. I
n alpine areas of the Colorado Front Range, modest loadings of N in deposit
ion have been associated with leakage of N to surface waters. On the Colora
do western slope, however, no leakage of N to surface waters has been repor
ted. A 1995 study that included early season under-ice water samples that w
ere not available in earlier studies showed that there is, in fact, N leaka
ge to surface waters in some western slope basins. Under-ice nitrate (NO3-)
concentrations were as high as 10.5 mu eq L-1, and only decreased to detec
tion limits in September Landscape type appears to be important in leakage
of N to surface waters, which is associated with basins having steep slopes
, thin soils, and large amounts of exposed bedrock. NO3- leakage compounds
the existing sensitivity to episodic acidification from low acid neutralizi
ng capacity (ANC), which is less than 40 mu eq L-1 in those basins.