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Numerous small alpine glaciers occupy the high elevation regions of the central and southern Sierra Nevada, California. An inventory based on 1∶24,000 topographic maps revealed 1719 glaciers and perennial snowfields for a total area of 39.15 ± 0.13 km2. The number of ‘true’ glaciers, versus non-moving ice, is estimated to be 122 covering 14.89 ± 0.08 km2 or 38% of the ice-covered area. Historic photographs, geologic evidence, and field mapping were used to determine the magnitude of area change over the past century at 14 glaciers. The area change between 1903 and 2004 ranged from −31% to −78%, averaging −55%. Based on these values rough estimates of volume change suggest an ice volume loss from 1903 (1.09 km3) to 2004 (0.43 km3) of 0.66 km3 (0.59 km3 water). Rapid retreat occurred over the first half of the 20th century beginning in the 1920s and continued through the 1960s after which recession ceased by the early 1980s and some glaciers advanced. Since the late 1980s glaciers resumed retreat with a rapid acceleration starting in the early 2000s. The relatively uniform timing of area changes in the study glaciers is a response to regional climate whereas the magnitude of change is influenced by local topographic effects. Area changes correlate significantly with changes in summer and winter air temperatures. Warmer winter temperatures warm the snowpack lengthening the summer melt season. Spring air temperatures and precipitation may also play an important role. The occurrence of spring snowfall can delay the onset of melt due to the increased surface albedo. Examining the influence of topographic variables we only found headwall height at the top of the glacier to show an influence on glacier change. Higher headwalls shadow the glacier from solar radiation reducing melt and enhancing snow accumulation via avalanching. If the glaciers continue to shrink at current (1972–2004) rates, most will disappear in 50–250 years.
The distribution of alpine tundra in the Adirondack Mountains of New York was investigated through a combination of field mapping and GIS analysis. Alpine tundra vegetation covers 26.3 ha (65 acres). Tundra patches are rare below an elevation of 1350 m although significant differences exist in mean tundra elevation between summits reflecting overall summit morphology. Tundra is generally more abundant, and extends to lower elevations on windward slopes with northerly and northwesterly aspects. Tundra patches on leeward slopes are found at higher elevations and are considerably larger, reflecting increased fragmentation on windward slopes and development of snowbank communities on leeward slopes. At a regional scale, the percentage of high-elevation land covered by tundra decreases from the northwest to southeast across the study area, suggesting that mountains upwind along the prevailing winter wind vector shield downwind summits, underscoring the role of exposure in limiting the upward growth of trees. Because exposure exerts a fundamental control over patch boundaries, shifts in the balance between arboreal and non-arboreal vegetation over time could be expected if changes occur in the frequency of icing events, the severity of winter storms, temperature, cloudiness, or prevailing wind directions.
Melilotus albus (white sweetclover) has invaded Alaskan glacial river floodplains. We measured cover and density of plant species and environmental variables along transects perpendicular to the Nenana, Matanuska, and Stikine Rivers to study interactions between M. albus and other plant species and to characterize the environment where it establishes. Melilotus albus was a pioneer species on recently disturbed sites and did not persist into closed canopy forests. The relationships between M. albus cover and density and other species were site-specific. Melilotus albus was negatively correlated with native species Elaeagnus commutata at the Nenana River, but not at the Matanuska River. Melilotus albus was positively correlated with the exotic species Crepis tectorum and Taraxacum officinale at the Matanuska River and T. officinale on the upper Stikine River. However, the high density of M. albus at a lower Stikine River site was negatively correlated with T. officinale and several native species including Lathyrus japonicus var. maritimus and Salix alaxensis. Glacial river floodplains in Alaska are highly disturbed and are corridors for exotic plant species movement. Melilotus albus at moderate to low densities may facilitate establishment of exotic species, but at high densities can reduce the cover and density of both exotic and native species.
In situ observations show increases in shrub cover in different arctic regions in recent decades and have been cited to explain the increases in arctic vegetation productivity revealed by satellite remote sensing. A widespread increase in shrub cover, particularly tall shrub cover, is likely to profoundly alter the tundra biome because of its influence on biogeochemical cycling and feedbacks to climate. To monitor changes in shrub cover, aid field studies, and inform ecosystem models, we mapped shrub cover across the North Slope of Alaska. First, images from the IKONOS and SPOT satellite sensors were used to detect tall (>1 m) and short shrub presence at high resolution (<5 m grid cells) in different parts of the domain. The resulting maps were then used to train a Random Forest regression algorithm that mapped total and tall shrub cover, expressed as a percent of the total surface area, at 30 m resolution from a mosaic of Landsat scenes. The final shrub cover maps correspond well with field measurements (r2 = 0.7, root mean square error = 17%, N = 24) and compared well with the existing vegetation type maps of the study area and a gridded temperature data set not used in the map generation.
Subsurface flow pathways of groundwater-fed streams were characterized on a floodplain terrace of the Toklat River, Alaska, in summer 2008, to establish the influence of local physicochemical variability upon macroinvertebrate communities. Streams proximal to the valley side (A sites) and to the main meltwater channel (B sites) were studied. Chloride and natural isotopic tracers (δ18O and δ2H) were used to identify water sources and flow pathways. Results indicated that flow in B sites was dominated by seepage of glacial meltwater through the alluvial aquifer. Streamflow at sites situated at higher elevations was ephemeral, and commenced with the seasonal rise in the groundwater table. In contrast, the physicochemistry of A sites was characteristic of seepage from valley-side debris fans, which maintained perennial flow to streams at lower elevations. Macroinvertebrate diversity was lower in ephemeral streams, likely due to colonization constraints. In June macroinvertebrate abundance was significantly positively correlated with the percentage contribution to streamflow from debris-fan seepage (p < 0.05) and with fine particulate organic matter concentration (FPOM) (p < 0.05); FPOM was correlated with debris fan seepage (p < 0.05). These relationships were not evident in July and August, when organic matter availability increased. Our study demonstrates that flow pathways and organic matter availability significantly influence macroinvertebrate communities in these groundwater-fed streams.
Previous research has indicated that modeling evapotranspiration (ET) in the Arctic Coastal Plain is challenging due to unique ecosystem conditions which include mosses, permafrost, and standing dead vegetation. A new version of the commonly used Biome–BGC (Biogeochemical Cycles) model (Arctic Biome–BGC) was developed that included: (1) a water storage and vertical drainage/infiltration routine that accounts for permafrost and mosses, (2) a modified representation of energy available at the surface which includes ground heat flux and simulates interception of incoming radiation by standing dead vegetation, and (3) a background evaporation routine that allows for moss and open water evaporation. In this study we investigated the sensitivity of model predictions to variations in parameter values, and to provide a conceptual validation of Arctic Biome–BGC. Using the generalized sensitivity analysis methodology, 13 parameters were evaluated. Results indicate that the model was sensitive to 8 of the 13 parameters. Seven of these parameters were introduced in the development of Arctic Biome–BGC and related to both energy reaching the ground surface and the amount of water stored within the soil and moss layers. The remaining sensitive parameter modulates the rate of snowmelt. These results validate the conceptual modifications included in the Arctic Biome–BGC model for estimating ET.
Environmental conditions associated with climate change, such as earlier snowmelt, warmer spring temperatures, and increased soil mineralization, have resulted in shifts in the timing of plant phenological events. We assessed the effects of fertilizer and herbivory on the phenology of 7 plant species from a boreal forest understory using long-term experimental plots in the southwest Yukon. Fertilizer and fencing treatments were initiated in 1990, and discontinued in half of each plot in 2000. There were few effects on phenology of either fertilizer or fencing. In some species, fertilizer affected the final phenological stage reached, but the presence and direction of the effect was species-dependent. Epilobium angustifolium was the only species where the timing of phenological stages responded to fertilization; early phenological stages were advanced with fertilizer. First leaf expansion for Arctostaphylos uva-ursi occurred earlier in fenced plots, although this effect disappeared in plots where the fencing treatment had been discontinued. We conclude that previously observed changes in species abundance with fertilizer treatments are likely not caused by changes in the phenology of these species, and are more likely due to fertilization imposed changes in vegetative growth.
The melting of glaciers in the European Alps has exposed new terrain in the last decades. Ground beetles (Carabidae, Coleoptera) are among the first colonizers of this new alpine land. Since 1999, we have studied the ground beetle assemblages of the recently deglaciated areas in the Hornkees glacier foreland (Zillertal Alps, Austria). Data were collected in July 1999, 2001, 2007, and 2009. Two species of Carabidae, Nebria jockischii and Nebria germari, were dominant in the areas immediately below the glacier in all sampling periods. The occurrence of Nebria jockischii larvae very close to the edge of the glacier strongly suggests that reproduction occurred in the area which had been ice-free for only one year. Comparison of the carabid beetle assemblages from the recently deglaciated areas with those from neighboring and longer exposed areas indicates that the first colonizers continuously expanded their range following the path of the glacial retreat. We hypothesize that Nebria jockischii populated the new alpine terrain by initial migration from the banks of the glacial stream, whereas Nebria germari probably colonized the recently deglaciated area by migration from the lateral moraines. These carabid beetles represent the first predatory insects in the initial phase of colonization of the Hornkees foreland.
While there has been a general trend of climate warming in the Arctic causing early snowmelt and prolonged growing season, climate change models for some areas in the High Arctic suggest increased snow accumulation, delayed spring melt, and consequently shorter growing season. We tested the vegetative and reproductive responses of Cassiope tetragona, an arctic shrub, to increased snow depth and delayed snowmelt using a snow fence experiment in Adventdalen, Norway (78°54′N, 18°01′E). We recorded seasonal shoot length, number of leaves, and capsules per shoot for three summers (2005–2007): two prior and one after the treatment began. Phenological events were recorded in 2007. The number of seeds per capsule was counted and seed germination was tested. Phenological development was significantly delayed behind fences, with lower shoot length, number of leaves, capsules, and seeds per shoot segment (16, 20, 54 and 11%, respectively) compared to controls, but there was no difference in these parameters between plots prior to fence establishment. Seed viability was unaffected by treatment. A delay in start of growing season due to delayed snowmelt decreased vegetative and reproductive performance of C. tetragona; earlier melt may therefore improve performance. This may lead to floral composition change in some high arctic locations.
The blue-white gentian, Gentiana leucomelaena (Gentianaceae), bears two colors of flowers (blue and white) within populations and on individual plants. We tested the hypothesis that these flower morphs have different mating systems associated with differences in pollinator species and visitation rates. This hypothesis was driven by the fact that colorful flowers are often more likely to be pollinated by diverse animal pollinators, and by the observation that white G. leucomelaena flowers always blossom earlier than blue ones in early spring, when few pollinators are available. This hypothesis was investigated by determining the pollination success, daily duration of flower opening, flower life span, the number of pollen grains and ovules per flower, pollinator visitation rates, and seed output for both color morphs during the flowering season of 2009. Hand-pollination and pollinator-exclusion experiments were also conducted to determine whether the two color morphs differed in their ability to self-pollinate. In general, blue flowers were found to have a trait combination that favors a significantly higher degree of pollinator specificity and cross fertilization, whereas white flowers were characterized as pollinator generalists and self-fertilizing. We speculate that the difference in the floral structure and function between blue and white flowers and their coexistence are likely adaptive in unpredictable and often pollinator-limited environments such as those found in the alpine meadows of the Qinghai-Tibet Plateau.
The diversity and distribution of aquatic benthic invertebrate communities of 17 lakes and 3 shallow ponds near Iqaluit and Rankin Inlet, Nunavut, Canada, were examined to assess patterns with respect to environmental gradients. Macroinvertebrates were collected using 500 µm mesh D-nets, and collected specimens were identified and enumerated; a total of 40 taxa were identified. Multivariate analyses (Redundancy Analysis) of relative abundance (%) data identified habitat (dominant substrate type), water chemistry, nutrients, and food/productivity (total phosphorus, total nitrogen, sulfate, dissolved oxygen, chlorophyll a), physical characteristics (maximum depth), catchment-related properties (lake elevation), and climate-related properties as significant environmental gradients influencing community composition. Ecosystem-scale lake characteristics had the greatest influence on benthic communities, followed by substrate type; however, there were substantive amounts of community variation influenced by the interaction between lake characteristics, substrate type, and regional differences. A number of environmental variables may have been significant due to differences in their values when comparing Rankin Inlet region sites versus Iqaluit region sites. The results agree with other studies indicating that benthic invertebrate communities are influenced by environmental gradients acting at different scales ranging from local, within-lake scales to large, regional scales.
We used a regionally modified global vegetation model (BIOME4-Tibet) to simulate biome distribution on the Tibetan Plateau under current climate conditions derived from regional meteorological observations. The bioclimatic limits (mean temperatures of the coldest and warmest months, minimum temperature, growing degree-days on 5 °C and 0 °C bases) for some key alpine plant functional types (temperate deciduous and conifer trees, boreal deciduous and conifer trees, desert woody plants, tundra shrubs, cold herbaceous plants, and lichens/forbs) were redefined based on regional vegetation-climate relationships. Modern vegetation maps confirmed that the BIOME4-Tibet model does a better job of simulating biome patterns on the plateau (gridcell agreement 52%) than the original BIOME4 model (35%). This improved model enhanced our ability to simulate temperate conifer forest, cool conifer and mixed forest, evergreen taiga, temperate xerophytic shrubland, temperate grassland and desert, and steppe and shrub tundra biomes, but made a negligible or reduced difference to the prediction of temperate deciduous forest, warm-temperate mixed forest, and three tundra biomes (erect dwarf-shrub tundra, prostrate dwarf-shrub tundra, and cushion forb, lichen, and moss tundra). Future modification of the vegetation model, by increasing the number of shrub and herb plant functional types, re-parameterization of more precise bioclimatic constraints, and improved representation of soil, permafrost, and snow processes, will be needed to better characterize the distribution of alpine vegetation on the Tibetan Plateau.
Substantial climate warming is predicted for high latitude regions and may have large impacts on tundra communities. As part of the International Tundra Experiment, this study characterized plant responses to natural and experimental variations in temperature at a subarctic, alpine tundra site. Non-destructive measures of plant reproduction and growth were monitored annually for four target species (Dryas octopetala, Lupinus arcticus, Polygonum viviparum, and Salix arctica) from 1999 to 2008. Plants were exposed to 8 years of an experimental warming treatment using open-topped chambers (OTCs). Temperatures in OTCs tended to be warmer at midday but cooler at night, with little net daily warming. OTCs had relatively little effect on plant responses, except for positive effects on reproductive characteristics of D. octopetala and P. viviparum. All target species except L. arcticus showed significant annual variations in vegetative and reproductive characteristics. Non-destructive measures used to monitor plant performance were significantly related to actual growth and reproductive output in most cases. Plant community composition did not show experimental effects nor were there consistent trends in composition over the 10 years of the study. Results of the study highlight individualistic species responses and the resilience of the plant community to observed temperature variations at this site.
Snowmelt is considered to affect growth of the boreal forest. So, we tested the hypothesis that late snowmelts delay the onset of xylogenesis and reduce xylem production in trees. Timings of xylem formation were compared to the dates of complete snowmelt combining a 7-year monitoring of cambial activity with meteorological records in four plots of Picea mariana in Quebec, Canada. The spatial and temporal variability in snowfall was analyzed separately, so taking into account both the long- and short-term effects. Snowfall occurred from October to May, with a snow cover lasting 173–199 days. Overall, xylogenesis lasted 99–117 days, with onsets ranging from late May to mid-June. The highest cell productions were observed in the warmest site, where the longest periods of growth were observed. Although at long-term the effects of snowmelt were significant for both onset and duration of xylogenesis and cell production, at short-term only the relationship between the onset of xylogenesis and the date of complete snowmelt was significant. The initial hypothesis could be confirmed only partially. The different responses to the long- and short-term analyses demonstrate the multi-scale influence of snowfall on tree growth and the determinant role of nutrient cycling in the productivity of boreal ecosystems.
At a high mountain lake in catchments of mica schist and gneiss rock in the European Alps, substantial increases in solute concentrations of sulfate, magnesium, calcium, silica, manganese, and nickel were observed over the past two decades. We hypothesized that microbial interactions with rock in the catchment of the lake might play an important role. We studied the chemolithotrophic activities resulting in the production of metal mobilizing metabolites (mineral acids). The potential of nitrifying and sulfur-oxidizing cultures derived from rock to mobilize elements from this rock when augmented with ammonium and thiosulfate was investigated in a 35 day laboratory study. Bacterial species prevailing in the indigenous nitrifying and sulfur-oxidizing mixed cultures were determined by 16S rRNA gene sequence based analysis. The average mineralogical composition of the rock sample was quartz (50%), feldspar (27%), muscovite (15%), chlorite (6%), and dolomite (2%). The increase of each soluble element in the presence of cultures relative to the conditions without microbes was related to the total element in the rock sample (leaching efficiency in percent). After 35 days, leaching efficiency was 7% (Ca), 2.4% (Mg), and 6.3% (Mn) in the presence of the nitrifying culture. In the presence of the sulfur-oxidizing culture, leaching efficiency was 13% (Ca), 5.7% (Mg), 5.4% (Mn), 1.3% (Zn), 0.2% (Fe), and 0.1% (Al). The results suggest that under conditions of abundant substrate availability, chemolithotrophic activity on catchment rock can contribute to the increase in soluble Ca, Mg, and Mn in lake water.
Coastal erosion rates locally exceeding 30 m y−1 have been documented along Alaska's Beaufort Sea coastline, and a number of studies suggest that these erosion rates have accelerated as a result of climate change. However, a lack of direct observational evidence has limited our progress in quantifying the specific processes that connect climate change to coastal erosion rates in the Arctic. In particular, while longer ice-free periods are likely to lead to both warmer surface waters and longer fetch, the relative roles of thermal and mechanical (wave) erosion in driving coastal retreat have not been comprehensively quantified. We focus on a permafrost coastline in the northern National Petroleum Reserve–Alaska (NPR-A), where coastal erosion rates have averaged 10–15 m y−1 over two years of direct monitoring. We take advantage of these extraordinary rates of coastal erosion to observe and quantify coastal erosion directly via time-lapse photography in combination with meteorological observations. Our observations indicate that the erosion of these bluffs is largely thermally driven, but that surface winds play a crucial role in exposing the frozen bluffs to the radiatively warmed seawater that drives melting of interstitial ice. To first order, erosion in this setting can be modeled using formulations developed to describe iceberg deterioration in the open ocean. These simple models provide a conceptual framework for evaluating how climate-induced changes in thermal and wave energy might influence future erosion rates in this setting.