Snowpack controls on nitrogen cycling and export in seasonally snow-covered catchments

Hen we provide an overview of current research activities on nitrogen (N) c ycling in high-elevation catchments of the Colorado Front Range. We then us e this information to develop a conceptual model of how snow cover controls subnivial (below snowpack) microbial processes and N leachate from the sno w-soil interface to surface waters. This model is based on research that id entifies subnivial processes as a major control on the leaching loss of N f rom soil during snowmelt. These subnivial soil processes are controlled by the development of the seasonal snow pack that insulates soil from cold air temperatures and allows heterotrophic microbial activity in the soil to im mobilize N. In this model the duration of snow-cover is divided into four s nowpack regimes zone I is characterized by shallow-short duration snowpacks , zone II is characterized by high interannual variability in snow depth an d duration, zone III is characterized by early developing, continuous snow cover, and zone IV is characterized by deep, long-duration snow cover vergi ng on perennial snowpacks. In zone I, soils remain frozen and there is litt le microbial activity and N leachate is high. In zone II, total microbial a ctivity is highly variable and the amount of N leachate is highly variable. In zone III, total microbial activity is high and there is little N leacha te. In zone IV, microbial activity is reduced because of carbon limitation and N leachate is high. This model suggests that a portion of the spatial a nd temporal variability observed in N export from these seasonally snow-cov ered systems is due to variability in winter snow cover across landscape ty pes and inter-annually within a landscape type. Copyright (C) 1999 John Wil ey & Sons, Ltd.