Nitrogen dynamics in two high elevation catchments during spring snowmelt 1996, Rocky Mountains, Colorado

Heuer, Kristi; Brooks, P. D.; Tonnessen, Kathy A.

doi:10.1002/(sici)1099-1085(199910)13:14/15<2203::aid-hyp859>3.0.co;2-k

Cited by 22 publications

(17 citation statements)

References 32 publications

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“…Niwot Ridge (40°03′N, 105°35′W; 3,500 m), a Long-Term Ecological Research site and UNESCO Biosphere Reserve, and Summit (39°31′N, 105°50′W; 3,750 m) are characterized by a low mean annual temperature (-3°C), a springtime precipitation maximum (mean 900-1,000 mm), most of which falls as snow, and a short (3 month) growing season. Soils at both sites are Cryocrepts underlain by granitic parent material, with high organic matter contents (13%), low N (1.0%) and mean pH of 5.5 (Theobald et al 1963;Burns 1980;Fisk and Schmidt 1995;Heuer et al 1999).…”

Section: Study Sites and Experimental Designmentioning

confidence: 99%

Variation in nitrogen-15 natural abundance and nitrogen uptake traits among co-occurring alpine species: do species partition by nitrogen form?

2002

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In the N-limited alpine tundra, plants may utilize a diversity of N sources (organic and inorganic N) in order to meet their nutritional requirements. To characterize species-level differences in traits related to N acquisition, we analyzed foliar δN, nitrate reductase activity (NRA) and mycorrhizal infection in co-occurring alpine species during the first half of the growing season and compared these traits to patterns of N uptake using a N (N-NH, N-NO) or C,N ([1]-C-N-glycine) tracer addition in the greenhouse. C enrichment in belowground tissue indicated that all species were capable of taking up labeled glycine, although only one species showed uptake of glycine potentially exceeding that of inorganic N. Species showing the most depleted foliar δN and elevated NRA in the field also tended to show relatively high rates of NO uptake in the greenhouse. Likewise, species showing the most enriched foliar δN also showed high rates of NH uptake. The ratio of NO:NH uptake rates and growth rate explained 64% and 72% of the variance in foliar δN, respectively, suggesting that species differ in the ability to take up NO and NH in the field and that such differences may enable species to partition soil N on the basis of N form.

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Section: Study Sites and Experimental Designmentioning

confidence: 99%

Variation in nitrogen-15 natural abundance and nitrogen uptake traits among co-occurring alpine species: do species partition by nitrogen form?

2002

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“…The primary connectivity between terrestrial soils and surface waters occurs during spring snowmelt in the Colorado Rocky Mountains (Baron & Campbell, 1997; Heuer et al ., 1999), but stream NO 3 − ‐N concentrations were elevated nearly year round during the 2000–2006 period. Winter temperatures are cold, and snow remains frozen until the spring thaw, thus there is little opportunity for the flushing of soil solutes during the fall and winter.…”

Section: Discussionmentioning

confidence: 99%

“…From late July to October, when stream NO 3 À -N concentrations were elevated in the post-2000 period, both forest N uptake and soil microbial activity were strongly limited by soil moisture, alleviated only by typical summer rain storms, which were rare in Colorado during this period (Monson et al, 2002;Groisman et al, 2005). The primary connectivity between terrestrial soils and surface waters occurs during spring snowmelt in the Colorado Rocky Mountains (Baron & Campbell, 1997;Heuer et al, 1999), but stream NO 3 À -N concentrations were elevated nearly year round during the 2000-2006 period. Winter temperatures are cold, and snow remains frozen until the spring thaw, thus there is little opportunity for the flushing of soil solutes during the fall and winter.…”

Section: Contribution Of Ecological Processes To Changes In N Dynamicsmentioning

confidence: 99%

Climate‐induced changes in high elevation stream nitrate dynamics

Schmidt

Hartman

2009

Global Change Biology

122

116

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Mountain terrestrial and aquatic ecosystems are responsive to external drivers of change, especially climate change and atmospheric deposition of nitrogen (N). We explored the consequences of a temperature-warming trend on stream nitrate in an alpine and subalpine watershed in the Colorado Front Range that has long been the recipient of elevated atmospheric N deposition. Mean annual stream nitrate concentrations since 2000 are higher by 50% than an earlier monitoring period of 1991-1999. Mean annual N export increased by 28% from 2.03 kg N ha À1 yr À1 before 2000 to 2.84 kg N ha À1 yr À1 in Loch Vale watershed since 2000. The substantial increase in N export comes as a surprise, since mean wet atmospheric N deposition from 1991 to 2006 (3.06 kg N ha À1 yr À1 ) did not increase. There has been a period of below average precipitation from 2000 to 2006 and a steady increase in summer and fall temperatures of 0.12 1C yr À1 in both seasons since 1991. Nitrate concentrations, as well as the weathering products calcium and sulfate, were higher for the period 2000-2006 in rock glacier meltwater at the top of the watershed above the influence of alpine and subalpine vegetation and soils. We conclude the observed recent N increases in Loch Vale are the result of warmer summer and fall mean temperatures that are melting ice in glaciers and rock glaciers. This, in turn, has exposed sediments from which N produced by nitrification can be flushed. We suggest a water quality threshold may have been crossed around 2000. The phenomenon observed in Loch Vale may be indicative of N release from ice features such as rock glaciers worldwide as mountain glaciers retreat.

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“…Soils and groundwater can regulate chemical composition of surface waters even in high elevation, complex terrain with much exposed bedrock, little soil development, and sparse vegetation Heuer et al 1999;Clow and Sueker 2000). The snowmelt chemical pulse evident in spring outflow can represent a flushing of stored groundwater in shallow subsurface reservoirs Mast et al 1995;Campbell et al 2000Campbell et al , 2002.…”

Section: Introductionmentioning

confidence: 99%

“…Nevertheless, the contribution of atmospheric deposition to export of N from high elevation ecosystems varies by geographic region depending on the different geology and watershed and landscape characteristics of the various regions. Further, during snowmelt, some alpine soils serve as nitrogen sources whereas some sub-alpine soils serve as sinks (Heuer et al 1999).…”

Section: Introductionmentioning

confidence: 99%

Water chemistry of high elevation Colorado wilderness lakes

Musselman

Slauson

2004

Biogeochemistry

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High elevation alpine and subalpine Rocky Mountain lakes in Colorado and southeastern Wyoming were examined to determine regional variability in water chemistry and their sensitivity to atmospheric deposition. Acid neutralizing capacity, pH, conductivity and concentrations of major anions and cations were compared. Regional differences in water chemistry are evident. The south-eastern most lakes have significantly higher pH, conductivity, ANC, and sums of acid and base concentrations than lakes in the other regions of the state. In contrast the northwestern most lakes are significantly more dilute than those from other regions. Despite these two regional differences, most regions are similar in having a wide range of variability in potential sensitivity of their lakes to acidification and nitrogen export. Many wilderness areas in western and eastern regions contains lakes that are extremely sensitive and other lakes not susceptible to deposition. Overall, 70% of the Colorado lakes are sensitive to acidification and 15% are extremely sensitive to acidification. All of the regions had lakes that are classified as susceptible or sensitive to acidification, with 12 of the 17 areas having all of their sampled lakes susceptible or sensitive. Generally NO 3 1À concentration in surface waters decreased from mid-season to late season; yet a large number of the lakes export NO 3 1À late in the season, suggesting nitrogen saturation. The results confirm the sensitivity of high elevation wilderness aquatic ecosystems in all regions of Colorado to acidification and nitrogen deposition.

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Nitrogen dynamics in two high elevation catchments during spring snowmelt 1996, Rocky Mountains, Colorado

Cited by 22 publications

References 32 publications

Variation in nitrogen-15 natural abundance and nitrogen uptake traits among co-occurring alpine species: do species partition by nitrogen form?

Variation in nitrogen-15 natural abundance and nitrogen uptake traits among co-occurring alpine species: do species partition by nitrogen form?

Climate‐induced changes in high elevation stream nitrate dynamics

Water chemistry of high elevation Colorado wilderness lakes

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