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Université de Fribourg

On source identification and alteration of single diesel and wood smoke soot particles in the atmosphere; an X-ray microspectroscopy study

Vernooij, Martine G. C. ; Mohr, M. ; Tzvetkov, G. ; Zelenay, V. ; Huthwelker, T. ; Kaegi, R. ; Gehrig, R. ; Grobéty, Bernard

In: Environmental Science and Technology, 2009, vol. 43, no. 14, p. 5339–5344

Diesel and wood combustion are major sources of carbonaceous particles in the atmosphere. It is very hard to distinguish between the two sources by looking at soot particle morphology, but clear differences in the chemical structure of single particles are revealed by C(1s) NEXAFS (near edge X-ray absorption fine structure) microspectroscopy. Soot from diesel combustion has a dominant spectral...

Université de Fribourg

Evidence of NAO control on subsurface ice accumulation in a 1200 yr old cave-ice sequence, St. Livres ice cave, Switzerland

Stoffel, Markus ; Luetscher, Marc ; Bollschweiler, Michelle ; Schlatter, Frédéric

In: Quaternary Research, 2009, vol. 72, no. 1, p. 16-26

Mid-latitude ice caves are assumed to be highly sensitive to climatic changes and thus represent a potentially interesting environmental archive. Establishing a precise chronology is, however, a prerequisite for the understanding of processes driving the cave-ice mass balance and thus allows a paleoenvironmental interpretation. At St. Livres ice cave (Jura Mountains, Switzerland), subfossil trees...

Université de Fribourg

Spatial analysis of rockfall activity, bounce heights and geomorphic changes over the last 50 years – A case study using dendrogeomorphology

Schneuwly, Dominique M. ; Stoffel, Markus

In: Geomorphology, 2008///doi:10.1016/j.geomorph.2008.05.043

Tree-ring series have been used to reconstruct 50 years of rockfall behavior on a slope near Saas Balen (Swiss Alps). A total of 796 cores and 141 cross sections from 191 severely injured conifer trees (Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra L.), combined with a series of aerial photographs, were used to investigate the evolution of the forest stand so...

Université de Fribourg

Rockfall and snow avalanche impacts leave different anatomical signatures in tree rings of juvenile Larix decidua

Stoffel, Markus ; Hitz, Oliver M.

In: Tree Physiology, 2008, vol. 28, no. 11, p. 1713-1720

Rockfall and snow avalanche events often cause injury to European larch (Larix decidua Mill.) trees, giving rise to the formation of callus tissue and tangential rows of traumatic resin ducts (TRDs). We analyzed and quantified anatomical reactions of juvenile trees injured before the start of the growing season by snow avalanches (15 trees, 324 cross sections) or rockfalls (18 trees, 270...

Université de Fribourg

Influence of canopy density on snow distribution in a temperate mountain range

López-Moreno, Juan I. ; Latron, J.

In: Hydrological Processes, 2008, vol. 22, no. 1, p. 117-126

We analyse spatial variability and different evolution patterns of snowpack in a mixed beech-fir stand in the central Pyrenees. Snow depth and density were surveyed weekly along six transects of contrasting forest cover during a complete accumulation and melting season; we also surveyed a sector unaffected by canopy cover. Forest density was measured using the sky view factor (SVF) obtained from...

Université de Fribourg

Unraveling the patterns of late Holocene debris-flow activity on a cone in the Swiss Alps: chronology, environment and implications for the future

Stoffel, Markus ; Conus, Delphine ; Grichting, Michael A. ; Lièvre, Igor ; Maître, Gilles

In: Global and Planetary Change, 2008, vol. 60, no. 3-4, p. 222-234

Debris-flow activity on the forested cone of the Ritigraben torrent (Valais, Swiss Alps) was assessed from growth disturbances in century-old trees, providing an unusually complete record of past events and deposition of material. The study of 2246 tree-ring sequences sampled from 1102 Larix decidua Mill., Picea abies (L.) Karst. and Pinus cembra ssp. sibirica trees allowed reconstruction of 123...

Université de Fribourg

Application of ash (Fraxinus excelsior L.) roots to determine erosion rates in mountain torrents

Hitz, Oliver M. ; Gärtner, Holger W. ; Heinrich, Ingo ; Monbaron, Michel

In: Catena, 2008, vol. 72, no. 2, p. 248-258

Due to the effect of global change, the potential risk of natural hazards occurring in alpine areas is expected to increase to an even higher risk-level than has been recorded during the last century. These global changes potentially also have distinct influences on fluvial processes in torrents causing erosion on slopes and riverbanks in forested areas. Dating the time of root exposure along...

Université de Fribourg

Comparison of different procedures to map reference evapotranspiration using geographical information systems and regression-based techniques

Vicente-Serrano, Sergio M. ; Lanjeri, S. ; López-Moreno, Juan I.

In: International Journal of Climatology, 2007, vol. 27, no. 8, p. 1103 - 1118

This paper compares different procedures for mapping reference evapotranspiration (ETo) by means of regression-based techniques and geographical information systems (GIS). ETo is calculated following the method of Hargreaves (HG) from a dense database of meteorological stations in the northernmost semi-arid region of Europe, the Ebro valley. The HG method requires the...

Université de Fribourg

Atmospheric circulation influence on the interannual variability of snow pack in the Spanish Pyrenees during the second half of the 20th century

López-Moreno, Juan I. ; Vicente-Serrano, Sergio M.

In: Nordic Hydrology, 2007, vol. 38, no. 1, p. 33-44

Large areas in the Spanish Pyrenees are covered by snow between December and April, especially above 1650 m a.s.l., the location of the cold season 0°C isotherm. However, a significant negative trend in Pyrenean snow pack was detected during the second half of the 20th century. This paper analyses the interannual evolution of snow accumulation in these mountains in relation to the variability of...