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

Abstract

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 leq 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.

Fluxes and chemistry of nitrogen oxides in the Niwot Ridge, Colorado, snowpack

“…Nitrate levels in the NWT snow average at *11 lL l -1 (Williams et al 2009), *4 times higher than the 2.9 lM mean snow nitrate concentration at Summit (Burkhart et al 2004). The annual nitrate loading in the snowpack at the Soddie site in 2006 was 1.4 kg N ha -1 (Williams et al 2009).…”

“…The annual nitrate loading in the snowpack at the Soddie site in 2006 was 1.4 kg N ha -1 (Williams et al 2009). Conversion of this amount of nitrate to gaseous (NO ?…”

“…NO 2 ), an interesting question warranting further investigation is whether these gases may potentially be a secondary source for snowpack NO 2 -and NO 3 -via R2-R5? Nitrogen cycling in the NWT snowpack was further evaluated by Williams et al (2009) using data from the Soddie site. They compared the volume-weighted mean (VWM) concentrations of nitrate for the winter and spring seasons at the NWT Saddle national atmospheric deposition program (NADP) site, which were 14 lM l -1 in 2006 and 16.5 lM l -1 in 2007; almost exactly the same as for the NADP site at the lower elevation C1 site.…”

Atmospheric deposition as a source of carbon and nutrients to an alpine catchment of the Colorado Rocky Mountains

“…Physical and chemical properties of snow are measured on a weekly basis at the Saddle and Soddie sites on Niwot Ridge; detailed sampling protocols have been presented in Williams et al (1999Williams et al ( , 2009). Precipitation quantity is measured as part of the NWT LTER program.…”

Winter and summer nitrous oxide and nitrogen oxides fluxes from a seasonally snow-covered subalpine meadow at Niwot Ridge, Colorado

“…Nitrate and ammonium are released from the seasonal snowpack in the form of an ionic pulse (Williams and Melack 1991;Williams et al 1996). Williams et al (2009) computed the total NO 3 --N loading in the snowpack at this site for both years at 1.4-1.7 kg N ha -1 , a range that exceeds the N lost as N 2 O by a factor of 5-8. In addition, the over-winter nitrate production rate through nitrification is considerably high at this site .…”