Storage and release of solutes from a subalpine seasonal snowpack: soil and stream water response, Niwot Ridge, Colorado

Much of the research on the chemistry of snow and surface waters of the western US, Europe, and Asia has been conducted in high-elevation catchments above treeline. Here we provide information on the solute content of the seasonal snowpack at the Soddie site on Niwot Ridge, Colorado, a subalpine site near treeline. We focus on the storage and release of both inorganic and organic solutes to the soils underneath the snowpack, and subsequent effects on the chemical and nutrient content of the underlying soil solution and the adjacent headwater stream. The concentration of inorganic nitrogen (N) stored in the seasonal snowpack at the Soddie site of about 11 μeq L⁻¹ was on the upper end of values reported for the northern hemisphere when compared to most areas of the Alps, Himalayas, and Tien Shan mountain ranges, but consistent with other reports of snowpacks in the Rocky Mountains. The storage of inorganic N in the snowpack at maximum accumulation averaged about 17 meq m⁻², or 170 eq ha⁻¹ (on the order of 2 kg-N ha⁻¹). Solutes were released from storage in the form of an ionic pulse, with a maximum concentration factor of about four. In contrast to the seasonal snowpack, the dominant form of N in the soil solution was dissolved organic N. Thus, soils underlying the seasonal snowpack appear to assimilate inorganic N released from storage in the snowpack and convert it to organic N. A two component mixing model suggests that the majority of streamflow was this year’s snowmelt that had infiltrated the subsurface and undergone subsequent biological and geochemical reactions. The inorganic N in surface waters at the headwaters of Como creek were always near or below detection limits, suggesting that this area at treeline is still N-limited.