Arctic and Alpine Research: Abstracts Vol. 31, No. 3

Arctic and Alpine Research: An Interdisciplinary Journal

Abstracts

Vol. 31, No. 3, August 1999

AD 2002 Declared by United Nations as "International Year of The Mountains" (pp 211-213)
Jack D. Ives and Bruno Messerli
Impact of River Discharge and Regional Climatology on the Decay of Sea Ice in the Laptev Sea during Spring and Early Summer (pp 214-229)
Jsrg Bareiss, Hajo Eicken, Alfred Helbig, and Thomas Martin
Summer sea-ice conditions in the Laptev Sea are characterized by high interannual variability. The impact of Lena River discharge, one of the Arctic's major rivers discharging roughly 525 km³ annually onto the Laptev shelf, and the regional meteorological regime affect the spring and summer ice regime of the Laptev Sea. Using ground and remote-sensing data and statistical analyses, it is shown that river discharge plays an insignificant role in the large-scale decay of the Laptev Sea ice cover. Hydrological and remote sensing data for the period 1979-1990 show that discharge/sea-ice interactions are confined to the coastal regions, with Lena River water flooding a fast-ice belt, roughly 25 km wide, in early to mid-June. Sea-ice decay and summer ice extent are shown to be affected most strongly by dynamic atmospheric forcing and by opening and enlargement of coastal polynyas in early spring.
Modeling the Determinants of Species Distributions in Antarctica (pp 230-241)
Andrew D. Kennedy
Considered from a functional ecological perspective, Antarctica's present-day terrestrial biota is the product of two sets of limiting factors: the continent's isolation from sources of immigrant propagules and the severe environmental stresses to which successful immigrants are exposed. The result is a low-diversity community composed almost entirely of stress-tolerant cryptogams, microarthropods, meiofauna, and microbes. In this paper a conceptual model is proposed that reduces the action of geographical isolation and environmental factors into a series of selection filters. It is argued that the low number of parameterizations needed to represent organism-environment interactions in Antarctica renders the simulation of macroscale patterns of species distributions a tractable proposition. Significantly, biotic interactions of the type that determine community structure at lower latitudes may be discounted. However, stochastic factors represent a source of "noise" that potentially reduce the model's predictive capability.
Climatic Significance of Light Rings in Timberline Spruce, Picea abies, Austrian Alps (pp 242-246)
Wolfgang Gindl
A ring-width and light-ring chronology was built from timberline spruce [Picea abies (L.) Karst.] in the eastern Alps in Austria. Comparison of the chronology spanning the period from 1750 to 1997 with a long-term temperature record revealed a close relationship to September and October temperatures and light-ring occurrence. Tracheidogram analysis of radial tracheid diameter and cell-wall thickness of light rings formed in 1912 compared with a reference year confirmed the influence of temperatures of this period on light-ring formation. It is concluded that light rings in timberline spruce are pointers for abnormally low temperatures during the last part of the growing season.
Dissolved Organic Carbon Concentration and Phytoplankton Biomass in High-mountain Lakes of the Austrian Alps: Potential Effects of Climatic Warming (pp 247-253)
Ruben Sommaruga, Roland Psenner, Ellen Schafferer, Karin A. Koinig, and Sabine Sommaruga-Wograth
Concentrations of dissolved organic carbon (DOC) and phytoplankton biomass (chlorophyll-a and biovolume) were measured during a survey of 57 high-mountain lakes of the Austrian Alps ranging from 1970 to 2890 m a.s.l. in elevation. Glacier-fed lakes had lower DOC (mean: 0.39 mg L^-1) than lakes not fed by glaciers (mean: 0.70 mg L^-1). Concentrations of DOC decreased with lake elevation and was 64% lower in lakes located between 2600 and 2800 (mean = 0.51, median = 0.47 mg L^-1) than between 1970 and 2200 m a.s.l. (mean = 1.40, median = 1.10 mg L^-1). Chlorophyll-a concentrations ranged from 0.2 to 10.6 mg L^-1 with a typical deep water maximum found in transparent lakes and a maximum close to the surface in glacier-fed lakes. Chlorophyll-a and direct estimations of biomass were highly significant correlated among lakes (r = 0.938, P < 0.001). DOC concentrations and chlorophyll-a were not significantly correlated (P > 0.05). The potential impact of climatic warming on the underwater ultraviolet radiation (UVR) was assessed on the basis of expected changes in concentration of the two most important factors controlling the attenuation of UVR in the water column of alpine lakes not fed by glaciers, i.e. the chromophoric DOC and phytoplankton. Considering a scenario of further climatic warming in the Alps, we hypothesize that the attenuation of underwater UVR will increase mainly as a consequence of higher inputs of allochthonous DOC to surface waters of alpine lakes. Application of an empirical model based on the attenuation of underwater UVR by DOC, indicated that between 25 and 50% of the lakes studied can be considered as sensitive to UVR, i.e., the value of the 1% UV attenuation depth was higher than the lake maximum depth.
Recovery of Productivity and Species Diversity in Tussock Tundra following Disturbance (pp 254-258)
Milan C. Vavrek, Ned Fetcher, James B. McGraw, G. R. Shaver, F. Stuart Chapin III, and Brian Bovard
Tundra ecosystems appear to recover slowly from disturbance, but little long-term data concerning plant diversity has been available. We examined recovery of tundra vegetation in Alaska, U.S.A., 23 yr after fire and 24 yr after bulldozing. Primary productivity, depth of thaw, and vascular plant diversity were compared between disturbed and undisturbed tundra to determine whether recovery was complete. Productivity, species richness, and diversity did not differ between burned and unburned plots. Depth of thaw, however, remained greater in burned relative to unburned plots. In contrast, depth of thaw was the only characteristic that did not differ between bulldozed and control plots. Productivity and species richness were greater in bulldozed plots, but diversity was less than control plots. The differences between the two disturbances suggest that, ultimately, recovery depends more on the impact of disturbance on vegetation than changes in the abiotic environment. Vegetative propagules persisted in the soil after fire, but not bulldozing. Therefore, recolonization after fire included plants from the seed bank and vegetative propagules. Vegetation on bladed plots was dominated only by seed bank species. Thus, more than two decades after disturbance, recovery of tundra vegetation appeared to be a function of the nature of the disturbance.
Effects of Temperature and Natural Disturbance on Growth, Reproduction, and Population Density in the Alpine Annual Hemiparasite Euphrasia frigida (pp 259-263)
Jorun Nylehn and Orjan Totland
The effects of temperature and "natural disturbance" on growth, seed production, and population density in the facultative hemiparasitic annual Euphrasia frigida (Scrophulariaceae) were examined in the middle alpine zone at Finse, southwest Norway. Experimentally elevated temperature increased growth and seed production significantly. Higher temperatures resulted in a small decrease in population densities during three seasons. The degree of "natural disturbance" did not influence growth and seed production, but population density was highest at intermediate disturbance levels. Thus, while temperature influences the performance of E. frigida, disturbance affected the population dynamics. The effects of temperature on growth and reproduction may also be indirect on hemiparasites, through improved conditions for the host plants under elevated temperatures. It is hypothesized that the predicted global warming will result in increased seed output from E. frigida plants in the middle alpine zone. Population densities, however, are likely to decrease under elevated temperatures, due to lower disturbance levels by frost heave and increased vegetation cover.
Soil and Plant CO₂ Emission in Response to Variations in Soil Moisture and Temperature and to Amendment with Nitrogen, Phosphorus, and Carbon in Northern Scandinavia (pp 264-271)
Lotte Illeris and Sven Jonasson
High-latitude ecosystems contain large soil carbon stocks. Climate change scenarios predict higher temperatures and changed precipitation pattern in the Arctic, which is likely to alter the ecosystem carbon (C) balance. With few exceptions most stud-ies of the ecosystem C balance in the Arctic have taken place in wet ecosystems, and it has been shown that the CO₂ efflux is likely to increase if the moisture level declines. However, large areas in the Arctic contain dry tundra, which is likely to make a different contribution to the C fluxes than wet tundra. In this study we examined the seasonal variations in ecosystem CO₂ emission in a dry subarctic heath in northern Scandinavia. Soil moisture level during most of the season was below 250% dry weight of the soil, which is a moisture level below which previous research has shown that microbial activity becomes increasingly moisture limited. Along with measurements throughout the season of CO₂ emission from plants and soil, soil temperatures, and moisture levels, we added N, P, sugar, and cornstarch. Except for a strong response to sugar addition, the short-term effect of soil temperature and moisture on seasonal CO₂ emission was much stronger than the responses to the additions. A regression model showed that respiration rates also in this relatively dry tundra are strongly controlled primarily by soil moisture conditions. However, the CO₂ efflux is likely to increase with increased moisture levels and decrease with drying, which is contrary to expected responses in wet tundra.
CO₂ Flux in Arctic and Alpine Dry Tundra: Comparative Field Responses under Ambient and Experimentally Warmed Conditions (pp 272-277)
J. M. Welker, K. B. Brown, and J. T. Fahnestock
We compared growing season CO₂ flux patterns between botanically similar arctic and alpine dry tundra ecosystems in Alaska and Colorado under ambient and experimentally warmed conditions. Measurements were taken during the 1997 growing season, 3 yr after the warming treatments were begun. Under ambient weather conditions, arctic dry tundra at Toolik Lake, Alaska, was a net source (4 g CO₂-C m^-2) of CO₂ to the atmosphere, while alpine dry tundra at Niwot Ridge, Colorado, was a net CO₂ sink (7 g CO₂-C m^-2) during the growing season. Experimental warming of arctic tundra by 1 to 3¡C, resulted in a seven-fold (32 g CO₂-C m^-2) increase in this ecosystem's carbon source activity. Similar warming in alpine tundra changed this ecosystem from a net carbon sink to a net carbon source of 8 g CO₂-C m^-2 over the growing season. In the Arctic, increased CO₂ efflux with warming was largely the result of increased rates of ecosystem respiration throughout the entire growing season, while in the alpine ecosystem respiration increased only early in the growing season. Rates of photosynthesis were generally not affected by experimental warming at either site. These data suggest that global warming will accentuate the carbon source activity of dry tundra in the northern foothills of Alaska and will change the net CO₂ exchange of alpine dry tundra in the northern Rocky Mountains from a net CO₂ sink to a source.
Impact of Precipitation and Grazing on the Water Vole in the Beartooth Mountains of Montana and Wyoming, U.S.A. (pp 278-282)
Marion Klaus, Robert E. Moore, and Ernest Vyse
This paper examines the influence of increased precipitation levels and grazing on the demographics of Microtus richardsoni. Water voles were trapped and marked during the summers of 1990, 1991, and 1992 along four headwater watersheds of the Clark's Fork of the Yellowstone River in Wyoming and Montana. The summer of 1992 had more than double the precipitation of either 1990 or 1991. During the wet summer of 1992, capture success was significantly greater, as was the proportion of young voles captured. In 1992, several factors contributed to increased water vole populations. There were significantly more indications of male reproductive activity. Class I water voles (13-49 g) of both sexes showed signs of reproductive activity indicating they were reaching sexual maturity at smaller body mass. Significantly more embryos/trap-killed female were found. In 1995, the water vole was listed as a sensitive species because it is rare and requires specific alpine riparian habitat that is declining and may be damaged by poor grazing practices. Capture success was significantly greater, and there were significantly more young water voles in ungrazed drainages. Measured indicators of reproductive activity did not vary significantly between grazed and ungrazed drainages. Grazing might affect survival of young water voles and should be studied further.
Ski Slope Vegetation of Mount Hood, Oregon, U.S.A. (pp 283-292)
Jonathan H. Titus and Shiro Tsuyuzaki
Ski slope vegetation on Mount Hood, Oregon, U.S.A. was surveyed to assess vegetation that has developed under a constant disturbance regime and the environmental factors that are important in structuring the vegetation. Ski runs extend from 1200 to 2200 m on the south face of Mount Hood. TWINSPAN distinguished 17 plant communities including 4 above treeline and 13 below treeline; 3 of the latter also occur in the forest adjacent to the ski runs. Elevation, which is correlated to temperature, precipitation, depth of snowpack, and timing of snow melt, is the most important variable structuring the vegetation. Soil texture is also important. Distance to the forest boundary influences the vegetation only at lower elevations. Most of the slopes we examined were thickly vegetated, except above treeline where vegetation is typically sparse. Non-native species were detected only at the lowest elevations and were infrequently dominant. Non-native species cover and richness were correlated with percent bare area. Relative to ski runs in other areas, those on Mount Hood have little non-native species invasion, probably due to the harsh conditions prevalent on the ski runs and to a relative lack of bare areas, which occupy 17% of the runs below treeline. The relative scarcity of bare areas may be a result of the relatively great age of the ski runs (64 yr). Above treeline there was no detectable difference in vegetative composition on and off the ski run, probably due to extensive trampling of the vegetation in the summer.
Mountain and Valley Winds of Lee Vining Canyon, Sierra Nevada, California, U.S.A. (pp 293-302)
Craig B. Clements
Observations have been made in a major, eastern canyon of the Sierra Nevada, and are the first documentation of the mountain and valley wind system in this range. The topography of the "Eastside" of the Sierra Nevada is unique, producing some interesting flow patterns. Surface and upper-air data have been collected during summer and winter from 1994 through 1997. The mountain wind and similarly the valley wind have been observed as regular features of Lee Vining Canyon. However, results have shown a complex wind regime where the normal up-canyon valley wind is often replaced with a down-canyon flow by mid-afternoon. This wind, which depends on a number of mechanisms, is more common during summer than winter which suggests that it may be thermally driven. During winter, katabatic flows have been observed in the upper reaches of the canyon proper, while a distinct valley wind dominated the lower regions of the canyon.
Deglaciation and Postglacial Vegetation History of the West Mountains, West-Central Idaho, U.S.A. (pp 303-311)
James P. Doerner and Paul E. Carrara
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.
Evaluation of Topographic Models of Rockfall Travel Distance for Use in Hazard Applications (pp 312-320)
Chris Keylock and Ulrik Domaas
Characterizing rockfall travel distances over a broad scale is time-consuming and expensive if a detailed numerical model is used that must account for varying boulder size and shape. In this paper four models are developed that utilize simple terrain parameters in order to predict extreme rockfall runout distances. Of these models, three are statistical and the fourth is a simple dynamics model. The results of our model testing suggest that a statistical model is advantageous if one wishes to determine rockfall hazard over a broad area quickly and effectively. In particular, the runout ratio approach is particularly useful at low exceedance probabilities because of the positively skewed distribution used. However, this model would appear to be more sensitive to the underlying data than other techniques. Consequently, the favored model may well depend upon the amount of data available from a given region.
Radio-echo Sounding at the Mittivakkat Gletscher, Southeast Greenland (pp 321-328)
Niels Tvis Knudsen and Bent Hasholt
Profiles along sounding lines and maps are presented of the glacier surface, bottom topography and ice thickness of Mittivakkat Gletscher. The maps are the result of the use of monopulse radio-echo sounding of ice thickness in about 450 points along profiles across the glacier. The position of most points was surveyed using a theodolite together with Electrooptic Distance Measurement. The Mittivakkat Gletscher consists of several accumulation basins which combine into a single ice tongue. There is a marked relief underneath the glacier, and it is possible to identify two major subglacial depressions, which probably strongly influence the subglacial drainage of water from the glacier. The bottom topography is reflected in the surface topography and in the position of crevassed areas. The following data were extracted: area: 17.6 km²; volume: 2024 X 10⁶ m³; ice thickness, H_mean: 115 m; ice thickness, H_max: 245 m.