Alpine ecosystems are particularly susceptible to disturbance due to their short growing seasons, sparse vegetation and thin soils. Increased nitrogen deposition in wetfall and changes in climate currently affect Green Lakes Valley within the Colorado Front Range. Research conducted within the alpine links chronic nitrogen inputs to a suite of ecological impacts, resulting in increased nitrate export. The atmospheric nitrogen flux decreased by 0.56 kg ha -1 year -1 between 2000 and 2009, due to decreased precipitation; however alpine nitrate yields increased by 40 % relative to the previous decade (1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999). Long term trends indicate that weathering products such as sulfate, calcium, and silica have also increased over the same period. The geochemical composition of thawing permafrost, as indicated by rock glacial and blockfield meltwater, suggests it is the source of these weathering products. Furthermore, mass balance models indicate the high ammonium loads within glacial meltwater are rapidly nitrified, contributing *0.5-1.4 kg N ha -1 to the growing season nitrate flux from the alpine watershed. The sustained export of these solutes during dry, summer months is likely facilitated by thawing cryosphere providing hydraulic connectivity late into the growing season. This mechanism is further supported by the lack of upward weathering or nitrogen solute trends in a neighboring catchment which lacks permafrost and glacial features. These findings suggest that reductions of atmospheric nitrogen deposition alone may not improve water quality, as cryospheric thaw exposes soils to biological and geochemical processes that may affect alpine nitrate concentrations as much as atmospheric deposition trends.

Small changes in the fl ux of energy, chemicals, and water to mountain catchments may invoke large changes in the local climate, ecosystem dynamics, and water quanti ty and quality. The Landscape Conti nuum Model (LCM) was developed in part to improve our understanding of how high-elevati on ecosystems might respond to future perturbati ons. We sampled water chemistry along the main stem of Boulder Creek in the Colorado Front Range from the foothills to the Conti nental Divide, along with four headwater catchments, to address two questi ons: (i) Is there value in extending the LCM concept to lower-elevati on headwater catchments? (ii) Is a "space-for-ti me" substi tuti on along an elevati onal gradient appropriate when there are changes in ecosystem type? Our results show that the hydrochemistry of headwater catchments along the elevati onal gradient of Boulder Creek was diff erent when compared to the main stem. Headwater catchments amplifi ed the fl uxes of inorganic and organic solutes when compared with sites at similar elevati ons along the main stem of Boulder Creek, consistent with the LCM. Our results also suggest a space-for-ti me substi tuti on along an elevati onal gradient is warranted for at least some biogeochemical processes when there is a switch from the snow to rain transiti on in annual precipitati on. For example, the high concentrati ons of base cati ons and dissolved organic carbon in the foothills catchment when compared with higher elevati on catchments is consistent with increased rates of biogeochemical cycling with increasing air temperature at lower elevati ons. However, the low-elevati on catchment had a lower specifi c discharge than other catchments with similar annual precipitati on, but higher percentages as snowfall, resulti ng in decreased fl uxes of these products.

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