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Alpine areas are vulnerable to nitrogen (N) deposition because of low N-buffering capacity and limited ability to resist change. The objective of the study was to assess if >30 years of N deposition have resulted in a decline in exchangeable base cations (CB) coupled with an increase of exchangeable aluminum (Al). We used soil and stream data sampled between 1982 and 2015 at Green Lakes Valley, Colorado Front Range to evaluate the change in an alpine catena. The CB in the surface horizons of the summit position decreased significantly from 45 cmolc kg−1 in 1982 to 2.3 cmolc kg−1 in 2015, while the exchangeable Al increased from 0.09 cmolc kg−1 to 0.7 cmolc kg−1 in the summit and from 8.9 cmolc kg−1 to 10.5 cmolc kg−1 in the toeslope. Spatiotemporal distribution of soil moisture along the catena exhibited the lowest values during the winter months because the temperature was below freezing. The soil moisture increased in early spring as soil-temperature rose. A Seasonal Kendall test (SK) showed that the soil moisture decreased along the catena by −0.007 m3 m−3 yr−1(P

High-elevation aquatic ecosystems are highly vulnerable to climate change, yet relatively few records are available to characterize shifts in ecosystem structure or their underlying mechanisms. Using a long-term data set on seven alpine lakes (3126 to 3620 m) in Colorado, USA, we show that ice-off dates have shifted 7 days earlier over the past 33 years and that spring weather conditions—especially snowfall—drive yearly variation in ice-off timing. In the most well studied lake, earlier ice-off associated with increases in water residence times, thermal stratification, ion concentrations, dissolved nitrogen, pH, and chlorophyll a. Mechanistically, low spring snowfall and warm temperatures reduce summer stream flow (increasing lake residence times) but enhance melting of glacial and permafrost ice (increasing lake solute inputs). The observed links among hydrological, chemical, and biological responses to climate factors highlight the potential for major shifts in the functioning of alpine lakes due to forecasted climate change.

Alpine ecosystems are particularly sus- ceptible to disturbance due to their short growing seasons, sparse vegetation and thin soils. Increased nitrogen deposition in wetfall and changes in climate currently affect Green Lakes Valley within the Col- orado Front Range. Research conducted within the alpine links chronic nitrogen inputs to a suite of ecological impacts, resulting in increased nitrate export. The atmospheric nitrogen flux decreased by 0.56 kg ha -1 year -1 between 2000 and 2009, due to decreased precipitation; however alpine nitrate yields increased by 40 % relative to the previous decade (1990-1999). Long term trends indicate that weath- ering products such as sulfate, calcium, and silica have also increased over the same period. The geochemical composition of thawing permafrost, as indicated by rock glacial and blockfield meltwater, suggests it is the source of these weathering products. Furthermore, mass balance models indicate the high ammonium loads within glacial meltwater are rapidly nitrified, contributing *0.5-1.4 kg N ha -1 to the growing season nitrate flux from the alpine watershed. The sustained export of these solutes during dry, summer months is likely facilitated by thawing cryosphere providing hydraulic connectivity late into the growing season. This mechanism is further supported by the lack of upward weathering or nitrogen solute trends in a neighboring catchment which lacks permafrost and glacial features. These findings suggest that reductions of atmospheric nitrogen deposition alone may not improve water quality, as cryospheric thaw exposes soils to biological and geochemical processes that may affect alpine nitrate concentrations as much as atmo- spheric deposition trends.

Hydrologic and hydrochemical studies have been conducted in Green Lakes Valley, Colorado Front Range, USA, above 3550 m since 1982. They show a classic seasonal hydrograph dominated by snowmelt and an earlier date for the start of spring flow and for peak flow over the period of record. This is consistent with patterns found at lower elevations in Colorado and throughout western North America. They also show an increasing trend in flows in September and October of 2.6 ±0.7 mm a−1 which is not found elsewhere and cannot be accounted for by increased autumn precipitation and the melting of surface ice. Because this late-season increase is not found at the highest elevations or in basins in which there is no evidence of permafrost, it seems best explained by the thawing of alpine permafrost at intermediate elevations. This is corroborated by an increase in the concentration of base cations and silica, and particularly in Ca2+ and SO4–, in the stream discharge starting in 2000. As with the physical hydrology, the geochemical signals have not been detected at the higher elevations in the basin, though they have previously been associated with streamflow from a small rock glacier in the valley. The combined evidence suggests the degradation of ice-rich permafrost on the north-facing slopes of the valley below 3700 m, where it has been detected at 3 m depth by geophysical surveys.

Shallow seismic refraction (SSR) and ground penetrating radar (GPR) are non-invasive geophysical techniques that enhance studies of the shallow subsurface deposits which control many geomorphic and biogeochemical processes. These techniques permit measuring the thickness and material properties of these deposits in sensitive alpine areas without using extensive pits and trenches that can impact current biogeospheric processes or distort them for future research. Application of GPR and SSR along 1.5 km of geophysical lines shows that layers of fine to coarse, blocky deposits of periglacial origin underlie alpine slopes in the vicinity of Niwot Ridge, Colorado Front Range. Interpretation of geophysical and drilling data shows that depth to bedrock ranges from 4 to >10 m and is not simply related to local slope. Our measurements suggest that ice lenses form seasonally beneath solifluction lobes; ice was not present in adjacent areas. Ice lenses are associated with local ponded water and saturated se...

We characterize the seasonal variation in the geochemical and isotopic content of the outflow of the Green Lake 5 rock glacier (RG5), located in the Green Lakes Valley of the Colorado Front Range, USA. Between June and August, the geochemical content of rock glacier outflow does not appear to differ substantially from that of other surface waters in the Green Lakes Valley. Thus, for this alpine ecosystem at this time of year there does not appear to be large differences in water quality among rock glacier outflow, glacier and blockslope discharge, and discharge from small alpine catchments. However, in September concentrations of Mg2+ in the outflow of the rock glacier increased to more than 900 µeq L−1 compared to values of less than 40 µeq L−1 at all the other sites, concentrations of Ca2+ were greater than 4,000 µeq L−1 compared to maximum values of less than 200 µeq L−1 at all other sites, and concentrations of SO reached 7,000 µeq L−1, compared to maximum concentrations below 120 µeq L−1 at the other sites. Inverse geochemical modelling suggests that dissolution of pyrite, epidote, chlorite and minor calcite as well as the precipitation of silica and goethite best explain these elevated concentrations of solutes in the outflow of the rock glacier. Three component hydrograph separation using end–member mixing analysis shows that melted snow comprised an average of 30% of RG5 outflow, soil water 32%, and base flow 38%. Snow was the dominant source water in June, soil water was the dominant water source in July, and base flow was the dominant source in September. Enrichment of δ18O from −10‰ in the outflow of the rock glacier compared to −20‰ in snow and enrichment of deuterium excess from + 17.5‰ in rock glacier outflow compared to + 11‰ in snow, suggests that melt of internal ice that had undergone multiple melt/freeze episodes was the dominant source of base flow. Copyright © 2005 John Wiley & Sons, Ltd.

Here we report on 3 years (1996 -1998) of measurements of organic and inorganic nitrogen (N) fluxes to and from Green Lakes Valley, a high-elevation ecosystem in the Colorado Front Range of the Rocky Mountains. Nitrate-N (NO3-N) was the dominant form of N in both precipitation and stream water. Annual precipitation contained 52% NO3-N, 32% ammonium-N (NH4-N), 9% dissolved organic N (DON), and 7% particulate organic N (PON). Annual export of N in streamflow was composed of 70% NO3-N, 4% NH4-N, 14% DON, and 12% PON. Thus the percentage of organic N increased from 16% of total N in precipitation to 26% of total N in streamflow. Subtracting inputs from outputs, Green Lakes Valley always shows net retention of inorganic N. The only form of N that showed net export was DON. DON export was low (0.18 to 0.13 kg ha 1 yr 1 ), with net export recorded in 2 years and basin retention recorded in 1 year. There was a seasonal pattern in the concentrations of inorganic N (NO3-N NH4-N) and organic N (DON PON). Concentrations of inorganic N were 15-25 mol L 1 during base flow, increased to 30 mol L 1 on the rising limb of the hydrograph during snowmelt runoff, then decreased to 5 mol L 1 on the recession limb of late summer, with a return to base flow values in the autumn. In contrast, organic N was 7-15 mol L 1 during base flow and decreased to near or below detection limits on the rising limb of the hydrograph, with a gradual but consistent increase on the recession limb and on into the autumn. The amount of N in dissolved organic matter changed over time, with the dissolved organic carbon (DOC):DON ratio decreasing from 45 on the rising limb of the hydrograph to 20 in the autumn. Spatially, there was a striking difference in the ratios of NO3-N and DON between talus and tundra areas. Nitrate concentrations in surface water draining talus areas were always greater than DON. In contrast, DON concentrations in surface water draining tundra areas were always greater than NO3-N. Concentrations of DON were not significantly correlated with DOC (R 2 0.04, p 0.05), indicating that controls on DON export may be different than controls on DOC export. Our results suggest that the ratio of the annual mass flux of inorganic N to organic N in stream waters may provide a novel index to evaluate the N status of terrestrial ecosystems from various biomes.

(2000). The Distant and Unsurveyed Country: A Woman's Winter at Baffin Island, 1857–58, Polar and Alpine Tundra, Eva Interglaciation Forest Bed, Unglaciated East-Central Alaska: Global Warming 125,000 Years Ago, Molluscan Palaeontology of the Pliocene-Pleistocene Kap Kobenhavn Formation, North Greenland, Etude de la Cryoclastie et de l'Haloclastie par Methode dilatometrique. Arctic, Antarctic, and Alpine Research: Vol. 32, No. 1, pp. 107-110.

Although limnologists have long been interested in regional patterns in lake attributes, only recently have they considered lakes connected and organized across the landscape, rather than as spatially independent entities. Here we explore the spatial organization of lake districts through the concept of landscape position, a concept that considers lakes longitudinally along gradients of geomorphology and hydrology. We analyzed long-term chemical and biological data from nine lake chains (lakes in a series connected through surface or groundwater flow) from seven lake districts of diverse hydrologic and geomorphic settings across North America. Spatial patterns in lake variables driven by landscape position were surprisingly common across lake districts and across a wide range of variables. On the other hand, temporal patterns of lake variables, quantified using synchrony, the degree to which pairs of lakes exhibit similar dynamics through time, related to landscape position only for lake chains with lake water residence times that spanned a wide range and were generally long (close to or greater than 1 year). Highest synchrony of lakes within a lake chain occurred when lakes had short water residence times. Our results from both the spatial and temporal analyses suggest that certain features of the landscape position concept are robust enough to span a wide range of seemingly disparate lake types. The strong spatial patterns observed in this analysis, and some unexplained patterns, suggest the need to further study these scales and to continue to view lake ecosystems spatially, longitudinally, and broadly across the landscape.

A continuous climate record since 195 1 at Niwot Ridge in the Colorado Front Range shows a decline in mean annual temperature, an increase in annual precipitation amount, and a decrease in mean daily solar radiation for the summer months. The increase in precipitation amount explains about half of the 200% increase in annual wet deposition of NO,- to Niwot Ridge over the last decade. Differences in climate parameters between 1994 and 1995 (increased snow depth and decreased net energy flux to the snowpack) resulted in a 4-5-fold increase in the magnitude of solute release from the snowpack in the form of an ionic pulse. In turn, the high chemical loading of strong acid anions in the seasonal snowpack and release of these solutes from the seasonal snowpack in the form of an ionic pulse is causing episodic acidification (ANC < 0 peq liter-l) in headwater catchments at present deposition levels. Small changes in climate parameters may cause large changes in the hydrochemistry of alpine streams. The changes in climate at Niwot Ridge are not in synchrony with lowland warming in the Great Plains to the east and serve as a reminder that climate in alpine areas is driven by local conditions and may be asynchronous with regional and global climate trends.

(2001). Short Reviews and Books Received. Arctic, Antarctic, and Alpine Research: Vol. 33, No. 3, pp. 380-382.

Seven years of discharge and water quality records define temporal and spatial patterns of solute movement in a Colorado alpine stream system. Dissolved solids concentrations are low, generally less than 30 mg 1−1 and occasionally less than 3 mg 1−1 at the highest elevations. Calcium is the dominant cation and bicarbonate and sulfate are the main anions. Temporal changes in solute concentrations are dominated by an annual cycle with high values in late winter and spring that decrease rapidly during early summer and then return more slowly through fall. This pattern corresponds to the seasonal streamflow regime and reflects differential elution of the snowpack by meltwater and changing proportions of surface and subsurface water in the streamflow. The amplitude of the annual cycle of solute concentration is reduced with increasing catchment area and where the groundwater contribution to flow is relatively high. In general, solute concentrations increase down valley but this trend is reversed in the case of biologically important solutes, such as nitrate and potassium. Rates of geochemical denudation are dominated by the volume of water discharge and thus are highest in the parts of the basin that accumulate the greatest depths of winter snow. They vary between 5 and 26 g m−2 yr−1 for different parts of the catchment and average less than 9 g m−2 yr−1. These rates are low compared to those from high-elevation catchments elsewhere but are an order of magnitude higher than rates of sediment removal from the basin.

[1] Source waters and flow paths of streamflow draining high-elevation catchments of the Colorado Rocky Mountains were determined using isotopic and geochemical tracers during the 1996 snowmelt runoff season at two subcatchments of the Green Lakes Valley, Colorado Front Range. A two-component hydrograph separation using δ18O indicates that new water dominated (82 ± 6%) streamflow at the 8-ha Martinelli catchment and old water dominated (64 ± 2%) at the 225-ha Green Lake 4 (GL4) catchment. Snowmelt became isotopically enriched as the melt season progressed, complicating the interpretation of source water models. Thus old water may be underestimated if the temporal variation in δ18O of snowmelt is ignored or extrapolated from point measurements to the catchment. Two-component hydrograph separations for unreacted and reacted waters using a single geochemical tracer were not always meaningful. Three-component hydrograph separations using end-member mixing analysis indicated that subsurface flow contributed more than two thirds to the streamflow at both catchments. Talus fields contributed more than 40% of the total discharge during summer at the GL4 catchment. A conceptual model was established for flow generation based on these results. It is suggested that surface water and groundwater interactions are much more important to the quantity and quality of surface water in high-elevation catchments than previously thought.

A biography of Benjamin Leigh Smith (1828–1913) is probably about a century overdue. It would never have been an autobiography given his diffidence and his refusal to seek personal publicity for th...

Permafrost landforms and regional reconstructions periglacial landforms glacial and fluviglacial landforms marine and lacustrine landforms polygenetic landforms cold climate slopes rock glaciers.

In the alpine catchment of Green Lakes Valley, the great variability in snow distribution is an important influence on environmental conditions. The snow cover has relatively little direct effect on geomorphic processes: avalanches of wet snow in Spring transport small volumes of debris to the valley floor and boulders are shifted locally in small sub-nival pavements. Indirectly, the influence of snow patterns on erosion is much greater. By changing the surface topography, it facilitates sediment transport across the tundra; through its control of hydrologic responses, its meltwater mediates sediment and solute movement; and by controlling the biota, it defines the source areas from which most sediments and solutes are derived.

Green Lakes Valley is a high (3500 m elevation), mid-continental drainage at relatively low latitude (40°N) which appears to have been influenced by a variety of environmental changes in the past h...

U nderstanding the form, behavior, and historical context of landscapes is crucial to understanding ecosystems on several temporal and spatial scales. Landforms, such as floodplains and alluvial fans, and geomorphic processes, such as stream erosion and deposition, are important parts of the setting in which ecosystems develop and material and energy flows take place. Over the long term, geomorphic processes create landforms; over a shorter term, landforms are boundary conditions controlling the spatial arrangement and rates of geomorphic processes. Ecosystems respond to both landforms and geomorphic processes. The history of geomorphic processes may be expressed directly in the composition and structure of vegetation, where geomorphic events and vegetation develop together. Geomorphic processes operating before the establishment of existing vegetation, or those subtly coexisting with the vegetation, may have their greatest influence on vegetation through controlling patterns of soil properties across a landscape, as in toposequences

This paper presents the model around which a geomorphic study of the impact of artificially augmented snowfall on alpine terrain has been designed. It consists of a two-order hierarchy which can be...

As part of a hazard mapping and evaluation study of the Kathmandu-Kakani area in the Middle Hills, Nepal, conducted as a United Nations/Unesco project, channel conditions at 43 stations on Thulo Khola and Ghatte Khola have been measured and peak discharges for the 1979 monsoon (a season of approximately normal precipitation) have been estimated. The results show that variations in the channels and the flows they carry in this tropical, high-relief area conform to the patterns established by other studies. This should allow hydrologic concepts and models that are derived from the long records and widespread studies of mid-latitude regions to be used in tropical mountains, where there are few direct observations. Flood hazards in the Kathmandu-Kakani area appear to be limited to those riparian zones which consist of constructed agricultural terraces. Damage to these terraces by channel expansion could provide a large influx of sediment to the fluvial system with consequent downstream siltation.

A century of study suggests many common characteristics in the geomorphic nature of high mountain areas. These include important structural influences in the landscape, usually on a variety of spatial scales, and contrasting climatic conditions (often confounded with vegetation distributions) which also exhibit a wide spatial variability. Most high mountain terrain also shows evidence of ancient erosion surfaces as well as that of past glacial action and other, less direct, consequences of late-Pleistocene environmental changes. The resulting landscape is one of high relief and highly variable potential energy. This is reflected in a history of recent erosion by large catastrophic events and a high potential for accelerated erosion where mountain terrain is impacted by man's activity. Such common characteristics suggest that mountain geomorphology be considered as a "regional" component within geomorphology.

Published records of the rainfall intensities and durations associated with shallow landsliding and debris flow activity suggests a limiting threshold for this type of slope instability. The limit ...

Precipitation acidity was monitored continuously from July to September 1983 at a well-instrumented research site located near the Continental Divide in central Colorado. Rainfall amount, temperature, pH, and specific conductance were determined using a prototype device consisting of a modified wet-only precipitation collector with appropriate sensors. Data were recorded automatically with microprocessor control by preset time intervals. Weekly wet-only composite precipitation samples were also collected. Precipitation totaled 190 mm during the period, all as rain. Sixty-five percent of the continuous pH measurements were between 3.40 and 4.10, with an average of pH 3.80. Values of pH greater than 5.00 were rare. Composite samples were significantly less acidic, and averaged pH 4.36. Precipitation pH typically decreased rapidly as a storm began, was lowest near or slightly after the time of maximum rainfall intensity, then increased slightly. Paradoxical low pH and low specific conductance were recorded, and it is possible that some initial continuous pH measurements were too low. Acid loading varied widely among storms, and may have resulted largely from short bursts of high-intensity, low-pH rainfall.