Mineral nitrogen transformations in and under seasonal snow in a high‐elevation catchment in the Rocky Mountains, United States

Williams, Mark W.; Brooks, P. D.; Mosier, A. R.; Tonnessen, Kathy A.

doi:10.1029/96wr02240

Cited by 116 publications

(106 citation statements)

References 32 publications

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“…These findings are consistent with those reported by Williams et al (1996) for an alpine location near the Saddle NADP site. This study also evaluated potential transformations of dissolved inorganic nitrate by adding isotopically-labeled ammonium and nitrate to separate snowpack plots, and reported no evidence for nitrification of ammonium or reduction of nitrate.…”

Section: Resultssupporting

confidence: 93%

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

et al. 2009

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The effect of snow cover on surfaceatmosphere exchanges of nitrogen oxides (nitrogen oxide (NO) ? nitrogen dioxide (NO 2 ); note, here 'NO 2 ' is used as surrogate for a series of oxidized nitrogen gases that were detected by the used monitor in this analysis mode) was investigated at the high elevation, subalpine (3,340 m asl) Soddie site, at Niwot Ridge, Colorado. Vertical (NO ? NO 2 ) concentration gradient measurements in interstitial air in the deep (up to *2.5 m) snowpack were conducted with an automated sampling and analysis system that allowed for continuous observations throughout the snow-covered season. These measurements revealed sustained, highly elevated (NO ? NO 2 ) mixing ratios inside the snow. Nitrogen oxide concentrations were highest at the bottom of the snowpack, reaching levels of up to 15 ppbv during mid-winter. Decreasing mixing ratios with increasing distance from the soilsnow interface were indicative of an upwards flux of NO from the soil through the snowpack, and out of the snow into the atmosphere, and imply that biogeochemical processes in the subnival soil are the predominant NO source. Nitrogen dioxide reached maximum levels of *3 ppbv in the upper layers of the snowpack, i.e., *20-40 cm below the surface. This behavior suggests that a significant fraction of NO is converted to NO 2 during its diffusive transport through the snowpack. Ozone showed the opposite behavior, with rapidly declining levels below the snow surface. The mirroring of vertical profiles of ozone and the NO 2 /(NO ? NO 2 ) ratio suggest that titration of ozone by NO in the snowpack contributes to the ozone reaction in the snow and to the ozone surface deposition flux. However, this surface efflux of (NO ? NO 2 ) can only account for a minor fraction of ozone deposition flux over snow that has been reported at other mid-latitude sites. Neither (NO ? NO 2 ) nor ozone levels in the interstitial air showed a clear dependence on incident solar irradiance, much in contrast to observations in polar snow. Comparisons with findings from polar snow studies reveal a much different (NO ? NO 2 ) and ozone snow chemistry in this alpine environment. Snowpack concentration gradients and diffusion theory were applied to estimate an average, wintertime (NO ? NO 2 ) flux of 0.005-0.008 nmol m -2 s -1 , which is of similar magnitude as reported (NO ? NO 2 ) fluxes

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Section: Resultssupporting

confidence: 93%

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

et al. 2009

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“…The average nitrate content of 1.3 mg N kg dry soil -1 and average ammonium content of *14 mg N kg dry soil -1 are similar to those reported by Williams et al (1996) and Neff et al (1994) for the growing season at a nearby dry alpine meadow at Niwot Ridge. Compared to a subalpine meadow soil (Cryorthent) in the European Alps (Freppaz et al 2007), ammonium content at NWT is similar and nitrate is one order of magnitude lower.…”

Section: Soil Nitrogen Poolssupporting

confidence: 83%

“…Snow density was measured at 10-cm height intervals in the snowpack *bi-weekly by digging a snowpit about *30 m away from the snow flux tower at a location with similar vegetation and slope characteristics, following the protocol of Williams et al (1996). During the 2-year experiment, corrected D N 2 O values ranged between 0.072 9 10 -4 and 0.140 9 10 -4 m 2 s -1 .…”

Section: Winter Flux Measurements and Calculationsmentioning

confidence: 99%

“…Lipson et al (2000) have shown that the decline in microbial biomass of soils reported during the snowmelt period (e.g., Brooks et al 1998;Brooks and Williams 1999;Williams et al 1996) may be caused by carbon limitation. In particular, longduration, early developing snowpacks such as at our site may promote conditions where the otherwise common pulse of available carbon substrate during snowmelt is reduced (Brooks et al 1997).…”

Section: Comparison With Other Ecosystemsmentioning

confidence: 99%

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

et al. 2009

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The soil emission rates (fluxes) of nitrous oxide (N 2 O) and nitrogen oxides (NO ? NO 2 = NO x ) through a seasonal snowpack were determined by a flux gradient method from near-continuous 2-year measurements using an automated system for sampling interstitial air at various heights within the snowpack from a subalpine site at Niwot Ridge, . During spring N 2 O emissions first peaked and then dropped sharply as the soil water content increased from the release of snowpack meltwater, while other gases, including NO x and CO 2 did not show this behavior. To compare and contrast the winter fluxes with snow-free conditions, N 2 O fluxes were also measured at the same site in the summers of 2006 and 2007 using a closed soil chamber method. Summer N 2 O fluxes followed a decreasing trend during the dry-out period after snowmelt, interrupted by higher values related to precipitation events. These peaks were up to 2-3 times higher than the background summer levels. The integrated N 2 O-N loss over the summer period was calculated to be 1.1-2.4 kg N ha -1 , compared to *0.24-0.34 kg N ha -1 for the winter season. These wintertime N 2 O fluxes from subniveal soil are generally higher than the few previously published data. These results are of the same order of magnitude as data from more productive ecosystems such as fertilized grasslands and high-N-cycling forests, most likely because of a combination of the relatively welldeveloped soils and the fact that subnivean biogeochemical processes are promoted by the deep, insulating snowpack. Hence, microbially mediated oxidized nitrogen emissions occurring during the winter can be a significant part of the N-cycle in seasonally snow-covered subalpine ecosystems.

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“…The decoupling of nutrient dynamics from the elution of other snowpack solutes during melt may infer the importance of the snowpack biota in nitrogen budgets (Hodson, 2006), but amendment experiments in alpine environments (Williams et al, 1996) fail to support this contention. The particular influence of total nitrogen and ammonium concentrations collinear with bacterial carbon production rates is apparent in all CCA models of snowpack bacterial communities reported here.…”

Section: Discussionmentioning

confidence: 99%

The dynamic bacterial communities of a melting High Arctic glacier snowpack

et al. 2013

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Snow environments can occupy over a third of land surface area, but little is known about the dynamics of snowpack bacteria. The effect of snow melt on bacterial community structure and diversity of surface environments of a Svalbard glacier was examined using analyses of 16S rRNA genes via T-RFLP, qPCR and 454 pyrosequencing. Distinct community structures were found in different habitat types, with changes over 1 week apparent, in particular for the dominant bacterial class present, Betaproteobacteria. The differences observed were consistent with influences from depositional mode (snowfall vs aeolian dusts), contrasting snow with dust-rich snow layers and near-surface ice. Contrary to that, slush as the decompositional product of snow harboured distinct lineages of bacteria, further implying post-depositional changes in community structure. Taxa affiliated to the betaproteobacterial genus Polaromonas were particularly dynamic, and evidence for the presence of betaproteobacterial ammonia-oxidizing bacteria was uncovered, inviting the prospect that the dynamic bacterial communities associated with snowpacks may be active in supraglacial nitrogen cycling and capable of rapid responses to changes induced by snowmelt. Furthermore the potential of supraglacial snowpack ecosystems to respond to transient yet spatially extensive melting episodes such as that observed across most of Greenland's ice sheet in 2012 merits further investigation.

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Mineral nitrogen transformations in and under seasonal snow in a high‐elevation catchment in the Rocky Mountains, United States

Cited by 116 publications

References 32 publications

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

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

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

The dynamic bacterial communities of a melting High Arctic glacier snowpack

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