Abstracts
Vol. 31, No. 4, November 1999
Mass Balance Features Derived from a Firn Core at Hielo Patagónico Norte, South America (pp 330-340)
Kenichi Matsuoka and Renji Naruse
Glaciological research was carried out in November and December 1996 in the accumulation area of Glaciar Nef, an eastward-facing glacier from Hielo Patagónico Norte (Northern Patagonia Icefield), South America. A 14.5-m-deep firn core (9.7 m water equivalent: w.e.) was obtained at 1500 m a.s.l., and air temperature and melting rate were also measured. Values of δ18O of 1- or 2-cm-thick samples in the upper 6 m of the firn fluctuated from -16 to -10‰, which are explained by variations in δ18O of precipitation. Below 6 m in the firn, δ18O was almost constant, due to percolation of large amounts of meltwater. It was considered that the upper 6 m was deposited during the prior winter; thus winter balance in 1996 was derived as +3.5 m w.e. Based on the measurement results and climatic data, winter and summer ablations were estimated at 0.0 and 3.4 m w.e., respectively, and summer accumulation at 2.1 m w.e. Then, net balance in the calendar year 1996 was estimated at about +2.2 m w.e. Comparison with previous studies and candidate drilling sites are also discussed.
The Decrease in Summer Surface Water Temperature with Altitude in Swiss Alpine Lakes: A Comparison with Air Temperature Lapse Rates (pp 341-352)
David M. Livingstone, André F. Lotter, and Ian R. Walker
Using miniature thermistors with integrated data loggers, the decrease in summer lake surface water temperature (LSWT) with increasing altitude a.s.l. was investigated in 10 Swiss Alpine lakes located between 613 m a.s.l. and 2339 m a.s.l. The LSWTs exhibit essentially the same short-term structure as regional air temperature, but are about 3 to 5°C higher than the air temperature at the altitude of the lake. LSWTs decrease approximately linearly with increasing altitude at a rate slightly greater than the surface air temperature lapse rate. Diel variations in LSWT are large, implying that single water temperature measurements are unlikely to be representative of the mean. Local factors will affect LSWT more than they affect air temperature, possibly resulting in severe distortion of the empirical relationship between the two. Several implications for paleoclimate reconstruction studies result. (1) Paleolimnologically reconstructed LSWTs are likely to be higher than the air temperatures prevailing at the altitude of the lake. (2) Lakes used for paleoclimate reconstruction should be selected to minimize local effects on LSWT. (3) The calibration of organism-specific quantitative paleotemperature inference models should not be based on single water temperature measurements. (4) Consideration should be given to calibrating such models directly against air temperature rather than water temperature. (5) The primary climate effect on the aquatic biota of high?altitude lakes may be mediated by the timing of the ice cover.
Diatom-based Transfer Functions for Inferring Past Climatic and Environmental Changes in Alaska, U.S.A. (pp 353-365)
Irene Gregory-Eaves, John P. Smol, Bruce P. Finney, and Mary E. Edwards
Surface sediment diatom assemblages from 51 Alaskan lakes, distributed along a north-south transect, were enumerated in order to develop transfer functions that could be used to make inferences of past climatic and environmental change. Environmental variables that were found to be the strongest predictors of the diatom assemblages, identified through Canonical Correspondence Analyses, were ionic and nutrient concentrations, as well as lake depth. A number of weighted-averaging (WA) regression-calibration techniques were employed to develop transfer functions for lake water conductivity, total phosphorus concentration, and lake depth, but simple WA with classical deshrinking produced the most robust models for all variables. The strength of these models (r2boot ranged between 0.52 and 0.53) is comparable to those generated from other northern calibration studies. Application of our models to fossil diatom assemblages could provide information on the magnitude of past environmental change, and may serve as a basis for assessing anthropogenically induced impacts.
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.
Late Wisconsin and Holocene Subalpine Forests of the Markagunt Plateau of Utah, Southwestern Colorado Plateau, U.S.A. (pp 366-378)
R. Scott Anderson, Jim Hasbargen, Peter A. Koehler, and Eric J. Feiler
The vegetation and climatic history of subalpine forests on the Colorado Plateau is documented from Lowder Creek Bog and Alpine Pond on the Markagunt Plateau. Pollen and macrofossil data demonstrate substantial changes at sites above 3150 m elevation during the last ca. 13,000 yr. During and after Late Wisconsin deglaciation, subalpine tree species (Picea engelmannii and Abies lasiocarpa) were rare or absent near Lowder Creek Bog site, but nonarboreal species predominated. P. engelmannii--A. lasiocarpa forest became well established there between 11,000 and 9800 yr BP and subalpine trees dominated this elevation throughout the Holocene. By ca. 8500 yr BP, however, Picea declined somewhat, with minimal pollen and macrofossil deposition occurring between ca. 8500 and 6400 yr BP. Picea trees may have thinned during this time or Picea may have expanded to higher elevations during this part of the Holocene, while Pinus ponderosa expanded at lower elevations. These changes were probably driven by warmer conditions with variable precipitation. Alternative explanations include hydroseral changes within the bog, or insect infestation on Picea. After ca. 6400 yr BP, more consistent Picea pollen influx suggests renewed importance around the bog, which has been maintained until the present. Abies lasiocarpa became more important after ca. 2700 yr ago. The pollen sequence supports an interpretation of high effective precipitation during the early Holocene, followed by warmer temperatures and somewhat variable precipitation after ca. 8500 yr BP. This sequence is most similar to other sites on and near the western, southern, and northeastern Colorado Plateau, where the maximum influence of monsoon activity may have declined by the end of the early Holocene. Declines in summer insolation probably contributed to Late Holocene cooling, with increasing effective precipitation at most sites, including Lowder Creek Bog.
Microscale Patterns of Tree Establishment near Upper Treeline, Snowy Range, Wyoming, U.S.A. (pp 379-388)
W. H. Moir, Shannon G. Rochelle, and A. W. Schoettle
We report tree seedling (mostly Picea engelmannii, some Abies lasiocarpa, very infrequent Pinus contorta) invasion into meadows at upper treeline in the Snowy Range, Wyoming, from 1994 to 1996. We used gradient analysis to relate this to environmental patterns, particularly plant community structure (as aggregates of plant life-forms) and persistence of snowpack in 1995 and 1996. Tree seedlings established best at sites where snow melted earliest; the site with the shortest growing season had fewest seedlings. Microsites dominated by vascular plants admitted few or no seedlings; seedlings were most likely to be found where cryptogams dominated. These findings have implications for forest advance under some climate scenarios and successional hypotheses.
Comparative Ordination of Low Arctic Vegetation Recovering from Disturbance: Reconciling Two Contrasting Approaches for Field Data Collection (pp 389-399)
Bruce C. Forbes and Olga I. Sumina
Multivariate statistics are applied to data on low arctic flora and vegetation in an effort to compare and interpret information derived from contrasting field methods normally considered to be incompatible. Data were collected using two of the most widespread field techniques currently in use in the circumpolar North: (1) standardized sampling, using a point frame-based protocol; and (2) more traditional phytosociological methods. The comparison is based on simultaneous objective (quantitative) and subjective (qualitative) sampling of identical stands of vegetation at and north of the latitudinal treeline in the Yamal Region of Northwest Siberia. The species composition of vegetation on anthropogenic primary surfaces is emphasized, but undisturbed tundra was also sampled. One hundred and sixty-five quadrats (1 x 1 m) were analyzed together with 33 relevés (5 x 5 m) using detrended correspondence analysis (DCA). The ordination results revealed very good correlation within anthropogenic vegetation stands. However, in ordination diagrams derived from samples within undisturbed tundra, samples were clearly separated based on quadrat size because many nonvascular taxa were missed in the large quadrats.
Occurrence of Alnus-Infective Frankia and Trifolium-Infective Rhizobium in Circumpolar Soils (pp 400-406)
Kerstin Huss-Danell, Halldor Sverrisson, Ann-Sofi Hahlin, and Kjell Danell
A survey was made of the occurrence of Frankia, infective on Alnus, in some 40 soils from the whole circumpolar area. Some of these soils were also tested for the occurrence of Rhizobium infective on Trifolium pratense. Infectivity tests were performed by growing test seedlings in soil or soil suspensions. Frankia was detected only in very few soils, in spite of extended experimental periods. When nodulation took place, nodulation was observed in few test plants. Several of nodulated test seedlings never turned green, suggesting that Frankia was ineffective in N2 fixation. An exception was soil from a site in the Faeroe Islands where nodulated Alnus had been introduced. This soil showed high nodulation ability and N2 fixation was likely. It is suggested that lack of infective Frankia in the circumpolar soils studied may be because Frankia had not been spread to these sites, but does not necessarily mean that soil conditions are negative for Frankia. Infective Rhizobium was rare in the soils studied. Lack of infective root nodule bacteria in potential sites for soil reclamation calls for the need to inoculate the plants and also provides the opportunity for introduction of selected bacterial strains without competition from an endogeneous soil microflora.
Movement of Seeds by the Burrowing Activity of Mole-Voles on Disturbed Soil Mounds in the Spanish Pyrenees (pp 407-411)
Daniel Gomez-García, S. M. Giannoni, Ramon Reiné, and Carlos E. Borghi
Three species of Microtus (voles) living in Pyrenean subalpine pastures brought seeds to the surface on vole mounds. This activity was studied to learn about the voles' influence on seed composition and vegetation gap colonization. Twenty-two plant species germinated from seed in the soil mounds. The plant composition of pastures was dominated by graminoids-hemicryptophytes. Nearly half of the seeds that occurred in mounds are of annual dicots able to quickly colonize the gaps and complete their vegetative cycle before the entry of perennial plants. Mound revegetation occurs chiefly by means of vegetative reproduction strategies. Nevertheless germination of seed brought to the surface can be important at the early stages of colonization after soil disturbance. Thus, such disturbances increase short-term plant diversity and patch heterogeneity.
Wind and Water Erosion of a Peat and Sand Area on Subantarctic Macquarie Island (pp 412-420)
J. M. Selkirk and L. J. Saffigna
This study presents rates of geomorphic processes on subantarctic Macquarie Island (54°30'S, 155°55'E) over a 3.3-yr period associated with erosion of a mixed sand and peat substrate at a site 180 m above sea level. Erosion pins were used to measure lowering of up to 43 mm yr-1 in the northern section of the site and accretion of 28 mm yr-1 in the southern section of the site. The present area of exposed sand and peat was compared with that in 1976 from aerial photography, which revealed the influence of the prevailing wind direction and the slope of the site. A thermoluminescence date of 22,100 ± 2800 yr BP (W2193) from sand and a radiocarbon date from peat of 1530 ± 30 yr BP (ß-94180) allowed partial reconstruction of environmental conditions at the site during the last 22,000 yr.
Alpine Debris-flows in Leirdalen, Jotunheimen, Norway, with Particular Reference to Distal Fans, Intermediate-type Deposits, and Flow Types (pp 421-435)
John A. Matthews, Richard A. Shakesby, Lindsey J. McEwen, Mark S. Berrisford, Geraint Owen, and Philip Bevan
The landforms and deposits associated with AD 1996 debris-flows at three sites in the low-alpine zone, Jotunheimen, southern Norway, are described and analyzed. Parallel levées, composed of diamicton, occur on the valley-side slopes but distinct frontal lobes are absent: instead, low-angle fans, up to about 50 m wide and ca. 500 m long have overridden vegetation in the footslope zone and in the valley bottom. Five facies are recognized in the fans: (1) cobble-rich diamicton, up to 50 cm thick; (2) pebble-rich diamicton, typically up to 30 cm thick; (3) pebbly sand lenses, up to about 15 cm thick; (4) massive silty sand or sandy silt (intermediate-type deposits) of thickness 5-15 cm; and (5) laminated fine sands and silts (typically a few cm thick). These succeed one another in a vertical and lateral sense. The landform-sediment assemblage and proximal-distal trends are explained by a four-stage model of an integrated debris-flow event in which (1) slope failure and sediment disaggregation are followed sequentially by (2) debris flow sensu stricto (cohesive debris flow), (3) wet mudflow or hyperconcentrated flow, and (4) water flow. Debris flow sensu stricto accounts for an estimated 48 to 51%, wet mudflow/hyperconcentrated flow 21 to 26%, and water flow 24 to 31%, by volume of material mobilized during each debris-flow event at two of the sites. Results highlight the potential complexity of debris-flow events and the importance of the associated relatively fine-grained intermediate-type deposits with little or no structure, which are attributed here to wet mudflow and/or hyperconcentrated flow. Water-lain deposits, also integral to the debris-flow event, tend to be thinner and finer, better sorted, and distinctly laminated.
Animals as Erosion Agents in the Alpine Zone: Some Data and Observations from Canada, Lesotho, and Tibet (pp 436-466)
Kevin Hall, Jan Boelhouwers, and Kevin Driscoll
Animals can exert a very strong impact on erosion and sediment transport in the alpine zone. Although the alpine zone is recognized for its abundance of animals, animal-soil erosion interactions have been poorly studied. Animals exert a direct influence through their burrowing and digging for food and also indirectly by opening the ground to climatic and geomorphic influences, e.g., rain splash, needle ice, and wind erosion. It is this synergy that is important for alpine erosion. Because the alpine zone is subject to freezing, frost action, and snow melt, exposed sediments and/or the availability of drainage through burrows can have a marked effect on sediment transport and slopes. On the steeper, less stable alpine slopes, the effects of loading can cause failure that produces arcuate slip scars, the exposed faces of which can also be exploited by geomorphic processes. In an attempt to study the effect of animals in the alpine zone, measurements of burrowing and digging based on quadrats (5m x 5m) along several transects were made in the alpine zone of the Rocky Mountains of Canada. Results indicated an average of 0.0243 m3 25 m-2 sediment displaced due to digging by rodents and a conservative estimation of sediment removal by rodents varying between 600 and 0.6408 m3 km-2 yr-1. Grizzly bears exerted the greatest erosional impact with as much as 0.4958 m3 25 m-2 being measured. Observations (and limited measurements) relating to the impact of animals on the landscape were also obtained from Lesotho and Tibet. These preliminary findings are presented in an attempt to exemplify the various and interrelated effects of animals, climate, and geomorphic process for the alpine zone. It is suggested that significantly more studies are urgently needed as the situation may be exacerbated by climatic warming and/or by the expansion of pastoralism resulting from attempts at sustainable development in developing nations. The impact of animals is an unquantified factor in many development studies, in geomorphic studies in polar or high-altitude environments, and in management plans for national parks or the exploitation of natural resources (e.g., through logging).
