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Results for “Arctic Antarctic and Alpine Research”

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At least 19 recordsLinked to original sources
USGS2007

Development of a spatial analysis method using ground-based repeat photography to detect changes in the alpine treeline ecotone, Glacier National Park, Montana, U.S.A.

Repeat photography is a powerful tool for detection of landscape change over decadal timescales. Here a novel method is presented that applies spatial analysis software to digital photo-pairs, allowing vegetation change to be categorized and quantified. This method is applied to 12 sites within the alpine treeline ecotone of Glacier National Park, Montana, and is used to examine vegetation changes over timescales ranging from 71 to 93 years. Tree cover at the treeline ecotone increased in 10 out of the 12 photo-pairs (mean increase of 60%). Establishment occurred at all sites, infilling occurred at 11 sites. To demonstrate the utility of this method, patterns of tree establishment at treeline are described and the possible causes of changes within the treeline ecotone are discussed. Local factors undoubtedly affect the magnitude and type of the observed changes, however the ubiquity of the increase in tree cover implies a common forcing mechanism. Mean minimum summer temperatures have increased by 1.5??C over the past century and, coupled with variations in the amount of early spring snow water equivalent, likely account for much of the increase in tree cover at the treeline ecotone. Lastly, shortcomings of this method are presented along with possible solutions and areas for future research. ?? 2007 Regents of the University of Colorado.

Montana↗
USGS2018

Mountain treelines: A roadmap for research orientation

For over 100 years, mountain treelines have been the subject of varied research endeavors and remain a strong area of investigation. The purpose of this paper is to examine aspects of the epistemology of mountain treeline research-that is, to investigate how knowledge on treelines has been acquired and the changes in knowledge acquisition over time, through a review of fundamental questions and approaches. The questions treeline researchers have raised and continue to raise have undoubtedly directed the current state of knowledge. A continuing, fundamental emphasis has centered on seeking the general cause of mountain treelines, thus seeking an answer to the question, "What causes treeline?" with a primary emphasis on searching for ecophysiological mechanisms of low-temperature limitation for tree growth and regeneration. However, treeline research today also includes a rich literature that seeks local, landscape-scale causes of treelines and reasons why treelines vary so widely in three-dimensional patterns from one location to the next, and this approach and some of its consequences are elaborated here. In recent years, both lines of research have been motivated greatly by global climate change. Given the current state of knowledge, we propose that future research directions focused on a spatial approach should specifically address cross-scale hypotheses using statistics and simulations designed for nested hierarchies; these analyses will benefit from geographic extension of treeline research.

Arctic, Antarctic, and Alpine Research↗
USGS2018

Variation in soil carbon dioxide efflux at two spatial scales in a topographically complex boreal forest

Carbon dynamics of high-latitude regions are an important and highly uncertain component of global carbon budgets, and efforts to constrain estimates of soil-atmosphere carbon exchange in these regions are contingent on accurate representations of spatial and temporal variability in carbon fluxes. This study explores spatial and temporal variability in soilatmosphere carbon dynamics at both fine and coarse spatial scales in a high-elevation, permafrost-dominated boreal black spruce forest. We evaluate the importance of landscape-level investigations of soil-atmosphere carbon dynamics by characterizing seasonal trends in soil-atmosphere carbon exchange, describing soil temperature-moisture-respiration relations, and quantifying temporal and spatial variability at two spatial scales: the plot scale (0–5 m) and the landscape scale (500–1000 m). Plot-scale spatial variability (average variation on a given measurement day) in soil CO 2 efflux ranged from a coefficient of variation (CV) of 0.25 to 0.69, and plot-scale temporal variability (average variation of plots across measurement days) in efflux ranged from a CV of 0.19 to 0.36. Landscape-scale spatial and temporal variability in efflux was represented by a CV of 0.40 and 0.31, respectively, indicating that plot-scale spatial variability in soil respiration is as great as landscape-scale spatial variability at this site. While soil respiration was related to soil temperature at both the plot- and landscape scale, landscape-level descriptions of soil moisture were necessary to define soil respiration-moisture relations. Soil moisture variability was also integral to explaining temporal variability in soil respiration. Our results have important implications for research efforts in high-latitude regions where remote study sites make landscape-scale field campaigns challenging.

Arctic, Antarctic, and Alpine Research↗
USGS2018

Deglaciation and postglacial vegetation history of the West Mountains, west-central Idaho, U.S.A.

The West Mountains, west-central Idaho, were deglaciated before ca. 11,500 BP, as indicated by radiocarbon ages and Glacier Peak tephra, at several sites in cirques. Pollen analysis of a sediment core, and plant macrofossils from sediments recovered from the cirque at the head of Van Wyck Creek, indicate that a closed spruce-pine forest surrounded the site from ca. 11,500 to 9800 BP. Early in this period, spruce (probably krummholz) was already growing near the present-day altitudinal limit of large upright spruce. Hence, the climate during this period was significantly warmer than before 11,500 BP. Between ca. 9800 and 3200 BP the climate was warmer and drier than present. Pollen data indicate that from ca. 9300 to the time of Mazama tephra deposition (ca. 6700 BP), the climate was warmer and drier than at any time since 11,500 BP. From ca. 6700 to 3200 BP there was a small decrease in temperature with a minor increase in effective moisture. Beginning ca. 3200 BP, the climate was characterized by cooler temperatures and more mesic conditions. Modern plant communities were established by ca. 1500 BP.

Idaho↗
USGS2018

Variability in winter mass balance of Northern Hemisphere glaciers and relations with atmospheric circulation

An analysis of variability in the winter mass balance (WMB) of 22 glaciers in the Northern Hemisphere indicates two primary modes of variability that explain 46% of the variability among all glaciers. The first mode of variability characterizes WMB variability in Northern and Central Europe and the second mode primarily represents WMB variability in northwestern North America, but also is related to variability in WMB of one glacier in Europe and one in Central Asia. These two modes of WMB variability are explained by variations in mesoscale atmospheric circulation which are driving forces of variations in surface temperature and precipitation. The first mode is highly correlated with the Arctic Oscillation Index, whereas the second mode is highly correlated with the Southern Oscillation Index. In addition, the second mode of WMB variability is highly correlated with variability in global winter temperatures. This result suggests some connection between global temperature trends and WMB for some glaciers.

Arctic, Antarctic, and Alpine Research↗
USGS2018

Periphyton dynamics in a subalpine mountain stream during winter

We conducted two experiments to determine the activity of and factors which control periphyton during winter in Stevensville Brook, Vermont. The first experiment during winter/spring 1994 examined the effect of a 300 to 450% difference in light and doubling of flow (low and high light, slow and fast flow) on periphyton chlorophyll a (chl a ) and ash-free dry mass (AFDM) from stream rocks and artificial substrata. A second experiment was performed to determine whether periphyton was nitrogen or phosphorus limited. In addition, stream water was sampled during fall/winter 1994/95 for nitrate (NO 3 ), ammonia (NH 4 ), soluble reactive phosphorus (SRP), and total phosphorus (TP) to determine the availability of nutrients in Stevensville Brook. Increases of up to 250% for AFDM and 600% for chl a during the first study indicated robust activity throughout the winter despite low temperatures and light. Flow had a negative effect and sampling date was found to have a significant effect on periphyton biomass (chl a and AFDM) while light was found to influence increases in AFDM on clay tiles only. Water analyses showed that SRP was less than 0.001 mg L −1 , NH 4 and TP were low and often undetectable, and NO 3 remained at about 0.20 mg L −1 . Results from the nutrient enrichment experiment showed a significant response of chl a to P but not N and no response of AFDM to enrichment with either N or P. In Stevensville Brook during winter, the algal community, as represented by the chl a concentration, is predominantly controlled by phosphorus concentrations and is influenced to a lesser extent by flow; the periphyton community as a whole, represented by AFDM, is controlled mostly by stream flow and light.

Vermont↗
USGS2018

Post-breeding movement and habitat use by wood frogs along an Arctic–Subarctic ecotone

By altering essential micro- and macrohabitat conditions for many organisms, climate change is already causing disproportionately greater impacts on Arctic and Subarctic ecosystems. Yet there is a lack of basic information about many species in northern latitudes, including amphibians. We used radio telemetry to study the post-breeding movements and habitat use of wood frogs ( Rana [= Lithobates ] sylvatica ) in the Hudson Bay Lowlands near Churchill, Manitoba, Canada. We tracked fifty-seven frogs (thirty-five males, twenty-two females; mean duration = 16.8 d) from three wetlands during the summers of 2015 and 2016. The three wetlands were representative of the Arctic–Subarctic ecotone, with each wetland surrounded by different proportions of boreal forest and tundra. Our results indicate that at the landscape scale, movement distances increased with temperature, and all frogs spent more time in the tundra habitat than in boreal forests, relative to the availability of each habitat type. At the microhabitat scale (1 m 2 plots), frogs selected areas with greater amounts of standing water, sedge, and shrubs. These results provide information on terrestrial movement patterns and critical habitat data for northern populations of wood frogs in a Subarctic environment, which will aid in understanding how climate change will affect amphibians in this rapidly changing ecosystem.

Manitoba↗
USGS2018

Lake levels in a discontinuous permafrost landscape: Late Holocene variations inferred from sediment oxygen isotopes, Yukon Flats, Alaska

During recent decades, lake levels in the Yukon Flats region of interior Alaska have fluctuated dramatically. However, prior to recorded observations, no data are available to indicate if similar or more extreme variations occurred during past centuries and millennia. This study explores the history of Yukon Flats lake origins and lake levels for the past approximately 5,500 years from sediment analyses guided by previous work on permafrost extent, thermokarst, and modern isotope hydrology. Sediments dated by 210 Pb and AMS radiocarbon indicate stable chronologies following initial lake initiation. Subsequent lithology is autochthonous, and oxygen isotope ratios of endogenic carbonate reflect lake level change at multiple time scales. Sediment results indicate high lake levels between approximately 4000 and 1850 cal yr BP, which is interpreted to reflect wetter-than-modern conditions. Lower lake levels with short-lived high stands during the past approximately 800 years reflect generally arid conditions with brief wet intervals similar to the region’s moisture regime today. The millennial trend is one of increasing aridity and corresponds closely with fire reconstructions and regional paleoclimatic trends. We conclude that high-magnitude lake-level fluctuations and decadal scale trends occurred before the observational period and are persistent hydroclimatic features of the Yukon Flats region.

Alaska↗
USGS2019

Glacier recession since the Little Ice Age: Implications for water storage in a Rocky Mountain landscape

Glacial ice is a significant influence on local climate, hydrology, vegetation, and wildlife. We mapped a complete set of glacier areas from the Little Ice Age (LIA) using very high-resolution satellite imagery (30-cm) within Glacier National Park, a region that encompasses over 400,000 hectares. We measured glacier change across the park using LIA glacier area as a baseline and used this to estimate change in glacier area and volume over time. An estimated 146 glaciers existed within the current boundaries of Glacier National Park during the LIA. By 2005, only 51 (35%) persisted. Nearly 90% of LIA glaciers had lost 50% of their area by 2005. This decrease in glacier area equates to an estimated loss of ice volume of 1.52 km3, or 1.37 km3 of water storage, roughly equivalent to 40% of Lake McDonald, the largest lake in the park. Understanding rates of deglaciation and implications for water storage and use can assist local resource managers and downstream communities in planning for change.

Montana↗
USGS2019

Potential shifts in zooplankton community structure in response to changing ice regimes and hydrologic connectivity

Changing Arctic climate may alter freshwater ecosystems as a result of warmer surface waters, longer open-water periods, reduced wintertime lake ice growth, and altered hydrologic connectivity. This study aims to characterize zooplankton community composition and size structure in the context of hydrologic connectivity and ice regimes in Arctic lakes. Between 2011 and 2016, we sampled the phytoplankton, zooplankton, and fish communities from a set of representative lakes on the Arctic Coastal Plain (ACP) of northern Alaska to determine potential food web responses to changing Arctic ecosystems. Multivariate analyses showed that time from ice-out had a strong influence on zooplankton community structure and that seasonal succession of zooplankton differed between lakes with varying hydrologic connectivity. Trends were observed suggesting that large-bodied zooplankton ( Daphnia , calanoid copepods) may be more prevalent in poorly connected lakes with low fish diversity. Large-bodied zooplankton displayed higher biomass in lakes with high occurrences of bedfast ice, while small-bodied zooplankton ( Bosmina , rotifers) displayed highest biomass in deeper lakes with low occurrences of bedfast ice. Our results contribute to limited knowledge of zooplankton in remote lakes of the ACP and suggest that the anticipated changes to aquatic ecosystems in the Arctic may include energetically less efficient plankton food webs.

Alaska↗
USGS2020

Alpine plant community diversity in species-area relations at fine scale

Observations of diversity in alpine vegetation appear to be scale dependent. The relations of plant species richness with surface processes and geomorphology have been studied, but patterns of beta diversity are less known. In Glacier National Park, Montana, diversity has been examined within 1 m 2 plots and for 16 m 2 plots across two ranges, with within-plot and across-range explanatory factors, respectively. The slopes of species–area equations for nested 4, 8, 12, and 16 m 2 plots were used as an indicator of beta diversity in Glacier National Park, where smaller and larger scales have been examined. The slopes were negatively related to a field assessment of surface stability and positively to the presence of talus—two sides of the same coin. A positive relationship with bedrock outcrops may be due to a misrepresentation of area for plants. The relationship of species–area slopes to plot-level gamma diversity was negative, weak, and marginally significant, and this variable did not enter the general linear model (GLM). Beyond simple differences in diversity with differences in environment, examination of beta diversity at a scale between that of earlier studies revealed surface processes and geomorphology as drivers that were also at a scale between those previously reported.

Arctic, Antarctic, and Alpine Research↗
USGS2021

Arctic insect emergence timing and composition differs across thaw ponds of varying morphology

Freshwater ponds provide habitats for aquatic insects that emerge and subsidize consumers in terrestrial ecosystems. In the Arctic, insects provide an important seasonal source of energy to birds that breed and rear young on the tundra. The abundance and timing of insect emergence from arctic thaw ponds is poorly understood, but understanding these fluxes is important, given the role of insects in food webs and current rates of environmental change at high latitudes. We aimed to evaluate emerging insect communities from thaw ponds with different morphologies, identify environmental covariates influencing insect composition, and describe temporal changes in insect abundance. We collected environmental information and insects that emerged over two growing seasons and examined the phenology and taxonomic composition of insects arising from different pond classes: low centered polygon, small coalescent, large coalescent, and trough ponds. Our findings indicated no differences in the timing of total emergence across ponds of varying morphology. Community dissimilarity was primarily associated with center or margin habitat and variables that differed strongly among pond classes. These insects, which provide important provisions for various species of birds, are likely to experience changes in emergence phenology and composition due to ongoing, rapid warming in the region.

Alaska↗
USGS2021

Evidence of glacial activity during MIS 4 in the Rocky Mountains, Colorado, USA

The Ziegler Reservoir fossil site near Snowmass Village, Colorado, provides a rare opportunity to examine environmental conditions in the Rocky Mountains during marine isotope stage (MIS) 4 (71–57 ka). Although recognized as a global-scale cold event, MIS 4 is typically absent from Rocky Mountain glacial chronologies because the geologic evidence was covered or destroyed during the subsequent, and more extensive, MIS 2 (Pinedale; 29–14 ka) glaciation. Ziegler Reservoir lies beyond the Pinedale glacial extent, which allowed for the preservation of a long-lived sequence of eolian sediments deposited in a lacustrine environment that spans from late MIS 6 (ca. 140 ka) through early MIS 3 (ca. 55 ka). Sediments dating to MIS 4 exhibit a significant increase in clay-sized particles, suggesting that the source areas, most likely nearby glacio-fluvial deposits, were enriched with fine-grained material at that time. We hypothesize that the elevated clay content was the result of rock flour production by nearby valley glaciers that were active in the Rocky Mountains during MIS 4. The results of our study illustrate how recognizing indirect evidence of glacial activity can result in a more complete record of past climate conditions than what could be achieved by the study of moraines alone.

Colorado↗
USGS2022

Mass balance of two perennial snowfields: Niwot Ridge, Colorado and the Ulaan Taiga, Mongolia.

Perennial snowfields are generally receding worldwide, though the precise mechanisms causing recessions are not always well understood. Here we apply a numerical snowpack model to identify the leading factors controlling the mass balance of two perennial snowfields that have significant human interest: Arapaho glacier, located at Niwot Ridge in the Colorado Rocky Mountains (United States), and a snowfield located in the Ulaan Taiga (Mongolia). The two locations were chosen because they differ in elevation, slope and aspect. However, both have sub-arctic climates and are located within semi-arid regions. We show that for these two locations the snowfield mass balance is primarily sensitive to air temperature and wind speed, followed by precipitation and dust deposition amounts. We find that the sensitivities are similar for the center of the snowfield as well as the margins.

Colorado↗
USGS2024

Climatic variability as a principal driver of primary production in the southernmost subalpine Rocky Mountain lake

Mountain lakes are sensitive indicators of anthropogenically driven global change, with lake sediment records documenting increased primary production during the twentieth century. Atmospheric nutrient deposition and warming have been attributed to changes in other Western mountain lakes, however, the intensity of these drivers varies. We analyzed a sediment core representing a 270-year record from Santa Fe Lake, New Mexico, to constrain the southern margin of Rocky Mountain lakes and quantify patterns of change in lake biogeochemistry, production, and diatoms since 1750. Lake sediments were dated using 210 Pb and analyzed for carbon (C), nitrogen (N), stable isotopes (δ 13 C, δ 15 N), diatoms, and phototrophic pigments. The abundance of cyanobacteria, purple sulfur-reducing bacteria, and diatom pigments were elevated during the stable conditions of the Little Ice Age; these phototrophic groups declined in the late 1800s and reached a minimum by 1950. From 1950 to 2020, sediments recorded an increased abundance of cryptophyte, diatom, and chlorophyte groups. The C and N (percentage dry mass) increased after 1950, whereas δ 15 N and δ 13 C values declined. Changes since the mid-twentieth century are contemporaneous with warming trends in the Southwest and modest deposition of atmospheric N. Our findings highlight the geographic variability of mountain lake responses to changing environmental conditions.

New Mexico↗
USGS2024

Characterizing vegetation and return periods in avalanche paths using lidar and aerial imagery

Snow avalanches are a hazard and ecological disturbance across mountain landscapes worldwide. Understanding how avalanche frequency affects forests and vegetation improves infrastructure planning, risk management, and avalanche forecasting. We implemented a novel approach using lidar, aerial imagery, and a random forest model to classify imagery-observed vegetation within avalanche paths in southern Glacier National Park, Montana, USA. We calculated spatially explicit avalanche return periods using a physically based spatial interpolation method and characterized the vegetation within those return period zones. The automated vegetation classification model differed slightly between avalanche paths, but the combination of lidar and spectral signature metrics provided the best accuracy (88–92 percent) for predicting vegetation classes within complex avalanche terrain rather than lidar or spectral signature metrics alone. The highest frequency avalanche return periods were broadly characterized by grassland and shrubland, but the influence of topography greatly influences the vegetation classes as well as the return periods. Furthermore, statistically significant differences in lidar-derived vegetation canopy height exist between categorical return periods. The ability to characterize vegetation within various avalanche return periods using remote sensing data provides land use planners and avalanche forecasters a tool for assessing the spatial extent of large-magnitude avalanches in individual avalanche paths.

Montana↗
USGS2025

Climate change impacts and adaptation in U.S. Rocky Mountain high-elevation ecosystems

From a resource management perspective, climate change is considered to be one of the main threats to high-elevation ecosystems. However, these valuable ecosystems present unique challenges to climate change adaptation (actions in response to environmental change and its effects in a way that seeks to reduce harm) due to their rugged and remote characteristics. Within this context, we summarized literature on climate change impacts and adaptation actions across U.S. Rocky Mountain high-elevation ecosystems to address the important question: What are the knowledge gaps for climate change responses within this ecosystem that limit the ability of natural resource managers to perform successful climate change adaptation? In addressing this question, we focus specifically on the U.S. Rocky Mountains but also place regional conclusions for climate change adaptation in high-elevation ecosystems into a broader context. Overall, we found that the complex topography and temporally variable climate of mountains promote potential refugia that may buffer alpine obligate species in the near-term but also challenge resource managers to consider biological lags within this ecosystem.

Colorado, Idaho, Montana, New Mexico, Wyoming↗