Dry Andes Research Articles

Glaciers and rock glaciers’ distribution at 28° SL, Dry Andes of Argentina, and some considerations about their hydrological significance

The area studied includes a little-known portion on the Dry Andes of the San Juan Frontal Cordillera, Argentina, where the hydrological significance of glaciers and rock glaciers was earlier never studied. The surveyed sector includes Cerro El Potro (5,870 m ASL) and nearby mountain chains (28°S). The predominant landforms in these areas were shaped in a periglacial environment superimposed on an earlier glacial landscape. These regions comprise abundant rock glaciers, a noteworthy rock glacier zone in the world, of which little is known in South America. This work employs geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude, aspect and slope using optical remote sensing techniques with GIS. Statistical estimation techniques were used based on a Digital Elevation Model (DEM) and aerial photos and Spot images interpretation. The specific density of rock glaciers’ estimation in the surveyed area (Argentine border) is 1.56% with corresponds to 38 rock glaciers with an area of 5.86 km2 and 0.12 km3 of water equivalent. Furthermore, the analytical results show that elevations >4,270 m ASL, a southeast-facing aspect, and slope between 2° and 40° favor the existence of rock glaciers, Finally, a comparison with glacier water equivalent, which covers an area of ~16 km2 and 0.9 km3 of water equivalent, shows that glaciers are the main stores of water at 28°S (Cerro El Potro Glacier). However, the importance of rock glaciers as water reserves in this portion of Argentina should not be underestimated.

The significance of rock glaciers in the dry Andes - reply to L. Arenson and M. Jakob

The significance of rock glaciers in the dry Andes - reply to L. Arenson and M. Jakob

The significance of rock glaciers in the dry Andes – A discussion of Azócar and Brenning (2010) and Brenning and Azócar (2010)

The significance of rock glaciers in the dry Andes – A discussion of Azócar and Brenning (2010) and Brenning and Azócar (2010)

Status and evolution of the cryosphere in the Andes of Santiago (Chile, 33.5°S.)

In the context of a general retreat of glaciers in the dry Andes, this study focuses on the state and recent evolution of debris-covered glaciers and permafrost-related landforms, especially rock glaciers, in the semiarid to semihumid Laguna Negra catchment, a part of the Andes of central Chile at 33.5°S, that is a key contributor of drinking water for the city of Santiago. We conducted catchment-scale geomorphological mapping, diachronic analysis of 1955 and 1996 orthophotographs and digital elevation models (DEMs), and the analysis of ground temperatures and their sensitivity to climate variation. Rock glaciers dominate spatially and in terms of water storage over glaciers (area ratio: 1.7:1; ratio of water equivalents: 1.5:1). An intense downwasting has affected both debris-covered and exposed glacier components in the Punta Negra subcatchment, a process that is associated with the growth of numerous thermokarst depressions. The altitudinal transect of ground temperature suggest that permafrost is widespread above ∼ 4000 m asl, although it can also occur at lower elevations on sheltered footslopes and within rock glaciers. The sensitivity analysis indicates that the near-surface ground thermal regime at high altitudes is strongly influenced by the snow cover disappearance date, which may therefore constitute an important control on the effect of climatic warming.

Hydrological and geomorphological significance of rock glaciers in the dry Andes, Chile (27°–33°S)

AbstractThe latitudinal‐altitudinal distribution of rock glaciers in the dry Chilean Andes between 27° and 33°S was analysed and their hydrological and geomorphological significance evaluated. Statistical estimation techniques were used based on digital elevation models and air photo interpretation, and sediment budget models were applied to assess surface‐lowering rates. The estimated specific density of rock glaciers in the study area is 1.4 per cent, which corresponds to 147.5 km2 and a water equivalent of 2.37 km3. A comparison with glacier water equivalents derived from revised glacier inventory data shows that rock glaciers are more significant stores of frozen water than glaciers between 29° and 32°S. The latitudinal‐altitudinal distribution of rock glacier limits roughly follows the mean annual air 0°C isotherm, but in the southern part of the study area it extends into elevations where modern regional mean annual air temperatures exceed 0°C. High Andean surface‐lowering rates inferred from rock glacier sediment budget models are in the order of 0.6–0.7 mm yr−1, which is comparable to previous results from the dry Chilean Andes, but lower than in the more humid Andes further south. Copyright © 2009 John Wiley & Sons, Ltd.

Statistical analysis of topographic and climatic controls and multispectral signatures of rock glaciers in the dry Andes, Chile (27°–33°S)

AbstractThe dual nature of rock glaciers as ice‐rich mountain permafrost and sediment storage systems results in a combination of geomorphic processes and energy balance components controlling their distribution. We use the generalised additive model (GAM), a semi‐parametric nonlinear method, to empirically analyse environmental controls and spectral characteristics of rock glaciers in the dry Andes of Chile based on presence/absence data at random point locations and predictor variables derived from digital elevation models and Landsat data. A combination of nonlinearly transformed local and catchment‐related terrain attributes (especially local and catchment slope and potential incoming solar radiation, PISR) characterises the geomorphic and climatic niche of rock glaciers. The influence of (latitude adjusted) relative PISR varies with mean annual air temperature (MAAT): high‐PISR sites are favourable for rock glacier development at lower MAATs and low‐PISR sites at higher MAATs. TM/ETM+ band 6 (thermal infrared) is an additional nonlinear predictor. The combination of topographic, climatic and multispectral data in a GAM achieves an excellent general discrimination (area under the ROC curve 0.87 on the model domain and 0.94 overall). In automatic rock glacier detection at a sensitivity of 70 per cent, this model achieves a false‐positive rate (FPR) of 6.0 per cent overall and 12.8 per cent on the model domain (bootstrap estimates: 7.9% and 16.8%). Dropping the multispectral data significantly increases the bootstrapped FPR by 36 per cent. Thus, the fusion of multisource data using modern nonlinear classification techniques is a promising step towards automatic rock glacier detection. Copyright © 2009 John Wiley & Sons, Ltd.

To what extent do natural disturbances contribute to Andean plant diversity? A theoretical outline from the wettest and driest parts of the tropical Andes

Abstract. This paper deals with natural disturbances and their impact on vascular plant enrichment at two climatically contrasting Andean ranges, i.e. the perhumid Cordillera Real in southern Ecuador and the arid Cordillera de Atacama in northern Chile. In the first case, main triggers for an additional input of pioneer species during succession stages initiated by perturbations are landslides, mudflows, and, to a lesser extent, cohort mortality, floods, and wildlife damages. Droughts and wind are stressors, which reduce plant growth but hardly plant diversity, in contrast to enhanced UV radiation with its mutagen effect. Though stress effects are similar in the Atacama, disturbance regimes differ considerably in this dry mountain environment. Here, most perturbations are of small dimension such as nitrogen inputs by feces of Lamoids and burrow activities of tuco-tuco mice, both of them fostering nitrophilous plant communities. Flooding, gelifluction, and other denudation processes such as sheet wash occur too, however, do not charge species enrichment in the dry Andes. Although the perhumid study site represents one of the world's plant diversity "hotspots" and, by contrast, the arid one a comparatively "coldspot", pioneer species during successive stages after natural disturbances contribute in a similar percentage to the total plant inventories (appr. 10% of the species numbers). Relatively seen, natural disturbances are most important for species enrichment in the Atacama (200–500 species per 10 000 km2), while most other ecological factors delimit plant survival. Instead, plant life at the Ecuadorian study area benefits from many climatic and edaphic site conditions, and consequently, disturbances are considered only one of many driving forces for its hotspot status (>5000 species per 10 000 km2).

THE ANDES: A GEOLOGICAL OVERVIEW FROM A BIOLOGICAL PERSPECTIVE

Abstract Geological events of biological importance in the history of the Andes include their impact on global climates through an influence on atmospheric circulation, rainfall patterns, and the atmospheric concentration of CO2; habitat diversification from lowlands through paramo to glaciated peaks; and migratory pathways ranging from discontinuous (mesic elements), highly discontinuous (paramo elements), barriers (to east-west migrations), to selective pathways (via the dry Andean valleys). The timing of these effects is a function of the uplift history of three (to nine) morphotectonic segments of the Andes resulting in (1) mostly lowland swamp and fluvial environments in the Cretaceous and Paleocene, (2) moderate uplands beginning in the Late Eocene (ca. 40 million years ago [Ma]), (3) appression of an offshore volcanic chain (the proto–Cordillera Occidental) in the Oligocene (ca. 30 Ma), (4) uplift of the proto–Cordillera Oriental and the Altiplano to about half their present altitude by the Middle ...

Application of frequency ratio and logistic regression to active rock glacier occurrence in the Andes of San Juan, Argentina

This study employs statistical modeling techniques and geomorphological mapping to analyze the distribution of active rock glaciers in relation to altitude, aspect, slope, lithology and solar radiation using optical remote sensing techniques with GIS. The study area includes a portion of the Dry Andes of the Cordillera Frontal of San Juan around 30°S latitude, where few geomorphological studies have been conducted. Over 155 rock glaciers have been identified, and 85 are considered active. The relationship between the variables and the rock glaciers distribution was analyzed using the frequency ratio method and logistic regression models. The analytical results show that elevations > 3824 m a.s.l., a south-facing or east-facing aspect, areas with relatively low solar radiation, and slope between 2° and 20° favor the existence of the rock glaciers, and demonstrate that lithology and slope exert major influences.

Bartonellosis

Bartonella spp are fastidious bacteria that occur in the blood of man and mammals; they are usually vector borne but can also be transmitted by animal scratches and bites. The bartonelloses of medical importance comprise Carrión's disease, trench fever, cat-scratch disease, bacillary angiomatosis, and peliosis hepatis. Carrión's disease, known as Oroya fever in the acute phase and verruga peruana (Peruvian wart) in its chronic form, has curious manifestations that, until recently, have been restricted in their geographic distribution to dwellers of the high, dry Andean valleys, but new sites of disease are emerging. Trench fever is associated with louse-borne disease and homelessness. Cat-scratch disease, bacillary angiomatosis, and peliosis hepatis are increasingly being recognized as causes of human disease, especially in susceptible population groups such as HIV-infected persons. The Bartonella spp are considered emerging human pathogens. The clinical manifestations, differential diagnosis, laboratory diagnosis, and treatment of these conditions are discussed.

The role of dispersal ability, climate and spatial separation in shaping biogeographical patterns of phylogenetically distant plant groups in seasonally dry Andean forests of Bolivia

AbstractAim To assess biogeographical patterns of Acanthaceae, Bromeliaceae, Cactaceae and Pteridophyta in Bolivian Andean seasonally dry forest islands and to explain current floristic differences between these islands by means of extrinsic (precipitation, elevation) and intrinsic (dispersal ability) factors.Location Ten isolated and disjunct seasonally dry forest areas in the Bolivian Andes and the adjacent seasonal forest areas of the Chiquitanía and Chaco regions.Methods We collated species data from recently updated and revised taxonomic treatments and herbarium collections for Acanthaceae, Bromeliaceae, Cactaceae and Pteridophyta, constructed floristic distance matrices to estimate beta diversity at the study sites and subjected them to Mantel correlation analyses. Multiple regressions on distance matrices allowed us to test the influence of geographical distance and environmental (elevation and precipitation) differences on floristic differentiation.Results Acanthaceae and Bromeliaceae, and to a lesser extent Cactaceae, showed coincident biogeographical patterns and suggested the presence of two seasonally dry forest groups in Andean Bolivia: one including all small isolated northern dry valleys and another including all southern valleys with connections to the lowland seasonal forests of the Chiquitanía and the Chaco. Most of the variation in the floristic distance matrices in these plant groups, with seed dispersal typically restricted to short distances, was explained by spatial separation between habitat islands. In contrast, pteridophytes showed a different biogeographical pattern. Their floristic differences between sites were determined by the environmental variables. The anemochorous and spore‐based dispersal system of this plant group seems to be a highly effective mechanism allowing pteridophytes to easily reach even the isolated dry valleys in inter‐Andean Bolivia.Main conclusions Current biogeographical patterns in dry Andean habitat islands can provide insights into the factors that control the processes of community assembly. We show that differences in community composition of phylogenetically distant plant groups in the understorey of seasonally dry forest islands can be explained by a combination of the habitat characteristics where the group is present (either precipitation, elevation or both) and, more interestingly, by group specific dispersal limitation (as inferred by geographical distance between island habitats).

On the role of subsurface heat conduction in glacier energy-balance modelling

AbstractWe discuss the inclusion of the subsurface heat-conduction flux into the calculation of the energy balance and ablation at the glacier–atmosphere interface. Data from automatic weather stations are used to force an energy-balance model at several locations on alpine glaciers and at one site in the dry Andes of central Chile. The heat-conduction flux is computed using a two-layer scheme, assuming that 36% of the net shortwave radiation is absorbed by the surface layer and that the rest penetrates into the snowpack. We compare simulations conducted with and without subsurface heat flux. Results show that assuming a surface temperature of zero degrees leads to a larger overestimation of melt at the sites in the accumulation area (10.4–13.3%) than in the ablation area (0.5–2.8%), due to lower air temperatures and the presence of snow. The difference between simulations with and without heat conduction is also high at the beginning and end of the ablation season (up to 29% for the first 15 days of the season), when air temperatures are lower and snow covers the glacier surface, while they are of little importance during periods of sustained melt at all the locations investigated.

Indicators of present global warming through changes in active layer-thickness, estimation of thermal diffusivity and geomorphological observations in the Morenas Coloradas rockglacier, Central Andes of Mendoza, Argentina

Abstract Temperature profiles from the active layer have been analysed for 2 sites on the composed rockglacier Morenas Coloradas, Cordon del Plata, Mendoza, Argentina, using monitoring data collected between 1989 and 2008 in order to characterize the impact of global warming in the cryolithozone of the Dry Andes at these latitudes (32°–33° S). A significant change in the active layer and suprapermafrost of this rockglacier of the Cordon del Plata is registered at the monitoring sites. The observed changes imply direct consequences for the cryogenic environment and the Andean creeping permafrost . The nose of the Morenas Coloradas rockglacier for example (Balcon I, 3560 m a.s.l.), already expresses inactivity; the permafrost table is found at great depth (7.5–9 m). Data collected at Balcon I and II allow to estimate the theoretical thermal diffusivity α at the active layer of Morenas Coloradas. Thermal diffusivity may be decisive for the study of cryogenic dynamics at other altitudes and latitudes in the region where data are still scarce. Low α values ( − 6 m 2 /s) correlate with occurrence of freezing and ice at low altitudes. While the glaciers are turning into small insignificant bodies in the high mountains, the periglacial level with creeping permafrost and linked with rockglaciers is expanding altitudinally, passing a transitional “rooting” area which is indirectly feeding the rockglaciers with their covered or “dead ice”. The ice of glacigenic origin contributes to the genesis of this type of permafrost. As the permafrost table is found at greater depths, the rockglaciers need to be monitored in order to define a balance between the upper periglacial level (in terms of altitude) with mountain continuous–quasi continuous permafrost and the lower periglacial level to where the lowest fronts of creeping permafrost are reaching. The variations of the cryogenic structure of the rockglaciers of the Cordon del Plata caused by warming processes, will have direct consequences for the volume of frozen sediments and therefore for the hydrology of the entire region, a fact that has to be taken into account for future socio-economic programs of the respective provincial governments.

A preliminary inventory of rock glaciers at 30°S latitude, Cordillera Frontal of San Juan, Argentina

The Dry Andes of the Cordillera Frontal of San Juan (30°S latitude) is characterized by high relief with peaks up to 5000 m a.s.l. This geological province is mainly made up of a suite of Triassic to Miocene volcanic rocks. Modern ice glaciers are small and few in number, and persistent snow fields are similarly small and scattered. The predominant landforms in these areas have been shaped in a periglacial environment superimposed on an earlier glacial landscape. A preliminary inventory map of rock glaciers was constructed using optical remote sensing techniques, digital topographic analysis and aerial photograph data organized in a geographic information system (GIS). Over 140 rock glaciers have been identified: 90% are active or inactive and the rest are fossil. A total of 88 rock glaciers are considered active. The most common periglacial features recognized in the area are talus glaciers, and only 23% are tongue-shaped glaciers.

Mitochondrial phylogeography and demographic history of the Vicuña: implications for conservation

The vicuña (Vicugna vicugna; Miller, 1924) is a conservation success story, having recovered from near extinction in the 1960s to current population levels estimated at 275,000. However, lack of information about its demographic history and genetic diversity has limited both our understanding of its recovery and the development of science-based conservation measures. To examine the evolution and recent demographic history of the vicuña across its current range and to assess its genetic variation and population structure, we sequenced mitochondrial DNA from the control region (CR) for 261 individuals from 29 populations across Peru, Chile and Argentina. Our results suggest that populations currently designated as Vicugna vicugna vicugna and Vicugna vicugna mensalis comprise separate mitochondrial lineages. The current population distribution appears to be the result of a recent demographic expansion associated with the last major glacial event of the Pleistocene in the northern (18 to 22 degrees S) dry Andes 14-12,000 years ago and the establishment of an extremely arid belt known as the 'Dry Diagonal' to 29 degrees S. Within the Dry Diagonal, small populations of V. v. vicugna appear to have survived showing the genetic signature of demographic isolation, whereas to the north V. v. mensalis populations underwent a rapid demographic expansion before recent anthropogenic impacts.

Response of some Andean cultivars of quinoa ( Chenopodium quinoa Willd.) to temperature: Effects on germination, phenology, growth and freezing

This article presents various experiments conducted under semi-controlled conditions to determine the effects of temperature on germination, phenology, growth and freezing in Chenopodium quinoa, a pseudocereal originating from the cold and dry Andean altiplano. Traditional landraces and recently released cultivars from distinct geographical origins were compared in order to look for local adaptation or breeding improvement with respect to low temperatures. Germination was evaluated in 10 cultivars at temperatures between 2 and 20 °C. Plant growth and development were examined in three cultivars over the growing cycle, under minimum temperature between 8 and 13 °C and maximum temperature between 20 and 28 °C. The thermal time concept was used to compare the various treatments and estimate the phyllochron, as well as the base temperature and optimum temperature for leaf appearance, time to flowering and leaf width growth. Two cultivars at the vegetative stage were compared for night freezing tolerance down to −6 °C, registering leaf exotherms and plant survival rate. The influence of plant water status and the possible protective or detrimental role of leaf epidermal vesicles were also examined. Low temperatures down to 2 °C delayed germination without impeding it totally. Base temperature for germination varied between −1.9 and +0.2 °C, with negative values in 9 cultivars out of 10. Thermal sensitivity in germination was not related to the geographic origin of the cultivars. Leaf appearance and time to flowering showed similar base temperatures near 1 °C. Phyllochron varied from 12.9 to 17.2 °C d with lower values in the two recently released varieties than in the traditional landrace. Leaf width increased from a base temperature around 6 °C up to an optimum temperature between 20 and 22.5 °C. Freezing experiments showed that no plant could survive after 4 h at −6 °C, while no serious effect was noted down to −3 °C. Leaf exotherms confirmed that ice nucleation occurred between −5 and −6 °C in most of the plants, the traditional landrace showing a lower freezing tolerance than the selected line. Low leaf water status delayed the freezing process, while leaf vesicles did not seem to play any protective or detrimental role towards leaf freezing. Implications of these results for quinoa crop adaptation to the Andean environment are discussed.

Successional Position of Dry Andean Dwarf Forest Species as a Basis for Restoration Trials

The successional affinity of nine woody species was inferred from the structure, diversity and disturbance history of the vegetation where these occurred. This was done in order to obtain a basis for a restoration experiment, currently in execution, in the dry Andean dwarf forest zone on the edge of the High Plain of Bogota (Colombia), at 2600–2950 m.a.s.l. We laid out 101 relevees in grassland and shrubland types in different stages of recovery, and in relatively little disturbed endemic Condalia thomasiana dwarf forest. The disturbance history of sites over the last ~60 years was inferred from aerial photograph series (1941–1991). CCA and logistic regression were applied to relate species composition to diversity, environment and disturbance history. All species showed a preference for certain structural groups. Also, a clear relation between species occurrence and vegetation diversity was found. Baccharis macrantha, and Dalea coerulea appeared relatively tolerant to grazing, while the remaining seven species reacted negatively. Soil clay content, base availability and organic carbon content was also an important factor for occurrence of each species. Invasion of grasslands by woody species is pioneered by Baccharis macrantha and followed by Dodonaea viscosa. Dalea coerulea was predominantly found on truncated clayey soils, which will probably not support Condalia dwarf forest. The hypothesized classification of the nine planted species to either pioneers or late-successional was fine-tuned. This exploratory study will be of use in the set-up of future succession-based restoration experiments, and for converting exotics afforestations to natural vegetation.

Mitochondrial Variation in Bolivian Populations of the Variable Antshrike (Thamnophilus Caerulescens)

AbstractThe Variable Antshrike (Thamnophilus caerulescens) is arguably the most polytypic thamnophilid, with males ranging from almost entirely jet black to nearly white. The four subspecies that occur in Bolivia are strikingly divergent in male plumage: T. c. aspersiventer (black with white-barred belly), T. c. connectens (black back and bib with white belly), T. c. dinellii (gray throat and back with rufous belly), and T. c. paraguayensis (light gray with white belly). To assess the genetic structure of those taxa in Bolivia, sequence variation at the mitochondrial cytochrome-b gene was screened in 126 individuals collected across transects spanning the plumage and vocal variation in the four forms. A 95-km-wide cline in haplotype frequencies from T. c. aspersiventer to T. c. dinellii was centered in the Serrania Cochabamba across an ecotone from humid to dry Andean foothill habitats. Thamnophilus caerulescens connectens is not a valid taxon, instead representing an introgressed population near the dinellii tail of the T. c. aspersiventer-T. c. dinellii hybrid zone. Although direct contact between T. c. dinellii and T. c. paraguayensis remains undocumented, the mitochondrial data were consistent with introgression along a broad cline extending across most of southern Bolivia. Overall, the transitions in mitochondrial frequencies were remarkably concordant with clinal changes in vocalizations among those same populations (Isler et al. 2005). Both studies highlight the need for increased sampling, in both the geographic extent and number of individuals per population, to address adequately the potential for clinal variation between populations that are not isolated geographically. A more restricted sampling design in the present study might have led to the erroneous conclusion that T. c. aspersiventer, T. c. dinellii, and T. c. paraguayensis have reciprocally monphyletic mitochondrial lineages, making them full species according to some species concepts.

05/00552 Wind tunnel study of coal dust release from train wagons

In the context of a general retreat of glaciers in the dry Andes, this study focuses on the state and recent evolution of debris-covered glaciers and permafrost-related landforms, especially rock glaciers, in the semiarid to semihumid Laguna Negra catchment, a part of the Andes of central Chile at 33.5°S, that is a key contributor of drinking water for the city of Santiago. We conducted catchment-scale geomorphological mapping, diachronic analysis of 1955 and 1996 orthophotographs and digital elevation models (DEMs), and the analysis of ground temperatures and their sensitivity to climate variation. Rock glaciers dominate spatially and in terms of water storage over glaciers (area ratio: 1.7:1; ratio of water equivalents: 1.5:1). An intense downwasting has affected both debris-covered and exposed glacier components in the Punta Negra subcatchment, a process that is associated with the growth of numerous thermokarst depressions. The altitudinal transect of ground temperature suggest that permafrost is widespread above ∼ 4000 m asl, although it can also occur at lower elevations on sheltered footslopes and within rock glaciers. The sensitivity analysis indicates that the near-surface ground thermal regime at high altitudes is strongly influenced by the snow cover disappearance date, which may therefore constitute an important control on the effect of climatic warming.

MITOCHONDRIAL VARIATION IN BOLIVIAN POPULATIONS OF THE VARIABLE ANTSHRIKE (THAMNOPHILUS CAERULESCENS)

Abstract The Variable Antshrike (Thamnophilus caerulescens) is arguably the most polytypic thamnophilid, with males ranging from almost entirely jet black to nearly white. The four subspecies that occur in Bolivia are strikingly divergent in male plumage: T. c. aspersiventer (black with white-barred belly), T. c. connectens (black back and bib with white belly), T. c. dinellii (gray throat and back with rufous belly), and T. c. paraguayensis (light gray with white belly). To assess the genetic structure of those taxa in Bolivia, sequence variation at the mitochondrial cytochrome-b gene was screened in 126 individuals collected across transects spanning the plumage and vocal variation in the four forms. A 95-km-wide cline in haplotype frequencies from T. c. aspersiventer to T. c. dinellii was centered in the Serrania Cochabamba across an ecotone from humid to dry Andean foothill habitats. Thamnophilus caerulescens connectens is not a valid taxon, instead representing an introgressed population near the din...