| 1. |
- Gottselig, N., et al.
(författare)
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Elemental Composition of Natural Nanoparticles and Fine Colloids in European Forest Stream Waters and Their Role as Phosphorus Carriers
- 2017
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Ingår i: Global Biogeochemical Cycles. - 0886-6236 .- 1944-9224. ; 31:10, s. 1592-1607
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Tidskriftsartikel (refereegranskat)abstract
- Biogeochemical cycling of elements largely occurs in dissolved state, but many elements may also be bound to natural nanoparticles (NNP, 1-100 nm) and fine colloids (100-450 nm). We examined the hypothesis that the size and composition of stream water NNP and colloids vary systematically across Europe. To test this hypothesis, 96 stream water samples were simultaneously collected in 26 forested headwater catchments along two transects across Europe. Three size fractions (~1-20 nm, >20-60 nm, and >60 nm) of NNP and fine colloids were identified with Field Flow Fractionation coupled to inductively coupled plasma mass spectrometry and an organic carbon detector. The results showed that NNP and fine colloids constituted between 2 ± 5% (Si) and 53 ± 21% (Fe; mean ± SD) of total element concentrations, indicating a substantial contribution of particles to element transport in these European streams, especially for P and Fe. The particulate contents of Fe, Al, and organic C were correlated to their total element concentrations, but those of particulate Si, Mn, P, and Ca were not. The fine colloidal fractions >60 nm were dominated by clay minerals across all sites. The resulting element patterns of NNP <60 nm changed from North to South Europe from Fe- to Ca-dominated particles, along with associated changes in acidity, forest type, and dominant lithology.
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| 2. |
- Stähli, M., et al.
(författare)
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A new in-situ sensor for large-scale snow cover monitoring
- 2004
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 38, s. 273-278
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Tidskriftsartikel (refereegranskat)abstract
- A new in situ sensor for the simultaneous measurement of snow water equivalent, snow density and liquid-water content is presented in this paper. The system consists of radio frequency transmission lines of up to 25 in length cast in a flat PVC band, which can be set up either horizontally to monitor single snow-layer properties or sloping from a mast to the soil surface to determine vertical snowpack properties. The dielectric coefficient along the flat-band cable is measured with a time-domain reflectometer at high frequencies, and with a low-frequency impedance analyzer. The performance of the sensor system was tested during two winter seasons (2001-03) at the high-alpine test site Weissfluhjoch, Davos, Switzerland. The cable suspension and set-up of the sloping cable was shown to be critical with regard to stability and the formation of unwanted air gaps along the cable. Overall, the sensing system proved quite robust and produced results in agreement with manual snowpack observations.
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| 3. |
- Lehning, Michael, et al.
(författare)
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Review of SNOWPACK and ALPINE3D applications
- 2004
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Ingår i: Snow Engineering V: Proceedings of the Fifth International Conference on Snow Engineering, 5-8 July 2004, Davos, Switzerland. - : Balkema. ; , s. 299-307
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Konferensbidrag (refereegranskat)
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| 4. |
- Lundin, Lars-Christer, et al.
(författare)
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Continuous long-term measurements of soil-plant-atmosphere variables at a forest site
- 1999
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Ingår i: Agricultural and Forest Meteorology. - 0168-1923 .- 1873-2240. ; 98-99, s. 53-73
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Tidskriftsartikel (refereegranskat)abstract
- It is a major challenge in modem science to decrease the uncertainty in predictions of global climate change. One of the largest uncertainties in present-day global climate models resides with the understanding of processes in the soil-vegetation-atmosphere-transfer (SVAT) system. Continuous, long-term data are needed in order to correctly quantify balances of water, energy and CO2 in this system and to correctly model it. It is the objective of this paper to demonstrate how a combined system of existing sensor, computer, and network technologies could be set up to provide continuous and reliable long-term SVAT-process data from a forested site under almost all environmental conditions. The Central Tower Site (CTS) system was set up in 1993-1994 in a 25 m high boreal forest growing on a highly heterogeneous till soil with a high content of stones and blocks. It has successfully monitored relevant states and fluxes in the system, such as atmospheric fluxes of momentum, heat, water vapour and CO2, atmospheric profiles of temperature, water vapour, CO2, short-and long-wave radiation, heat storage in soil and trees, sap-dow and a variety of ecophysiological properties, soil-water contents and tensions, and groundwater levels, rainfall and throughfall. System uptime has been more than 90% for most of its components during the first 5 years of operation. Results from the first 5 years of operation include e.g., budgets for energy, water and CO2, information on important but rarely occurring events such as evaporation from snow-covered canopies, and reactions of the forest to extreme drought. The carbon budget shows that the forest may be a sink of carbon although it is still growing. The completeness of the data has made it possible to test the internal consistency of SVAT models. The pioneering set-up at the CTS has been adopted by a large number of SVAT-monitoring sites around the world. Questions concerning tower maintenance, long-term calibration plans, maintenance of sensors and data-collection system, and continuous development of the computer network to keep it up to date are, however, only partly of interest as a research project in itself. It is thus difficult to get it funded from usual research-funding agencies. The full value of data generated by the CTS system can best be appreciated after a decade or more of continuous operation. Main uses of the data would be to evaluate how SVAT models handle the natural variability of climate conditions, quantification of water. carbon and energy budgets during various weather conditions, rind development of new parameterisation schemes in global and regional climate models.
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| 5. |
- Gustafsson, D., et al.
(författare)
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Multi-criteria parameterisation of a numerical forest snow processes model : analysis of parameter uncertainty and governing processes
- 2006
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Ingår i: Geophysical Research Abstracts. - : European Geosciences Union (EGU).
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Forest snow processes such as snow interception evaporation and the influence of the canopy on snow cover melt are important for the land surface water and heat balance. Difficulties to model snow interception are due to both limitation in the understanding of the governing processes and in parameter estimations. In this study we parameterise a numerical simulation model (Alpine3D) using multiple calibration variables - snow water equivalent, snowmelt, throughfall, and runoff - through a Monte-Carlo procedure, which enables parameter uncertainty estimations and identification of the sensitivity in the model to different processes. The analysis is based on a data from a sub-alpine spruce forest in Alptal, Switzerland. Results show how the multi-criteria approach is able to reduce the number of parameter combinations that fulfil the critera. Further more, it is shown that parameters governing the turbulent exchange from the canopy and the snow cover were most important for the simulation of the snow cover evolution, whereas the runoff and throughfall was more sensitive to direct throughfall and interception capacity parameterisations.
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| 6. |
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| 7. |
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| 8. |
- Keller, T, et al.
(författare)
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Impact of artificial snow and ski slope grooming on the snow pack properties and the soil thermal regime in a sub-alpine area
- 2004
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Ingår i: Annals of Glaciology. - : International Glaciological Society. - 0260-3055 .- 1727-5644. ; 38, s. 314-318
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Tidskriftsartikel (refereegranskat)abstract
- Studies have indicated that the soil on groomed ski slopes may be subjected to more pronounced cooling than the soil below a natural snowpack. We analyzed the thermal impacts of ski-slope preparation in a sub-alpine ski resort in central Switzerland (1100 in a.s.l.) where artificial snow was produced. Physical snow properties and soil temperature measurements were carried out on the ski slope and off-piste during winter 1999/2000. The numerical soil-vegetation-atmosphere transfer model COUP was run for both locations, with a new option to simulate the snowpack development on a groomed ski slope. Snow density. snow hardness and thermal conductivity were significantly higher on the ski slope than in the natural snowpack. However, these differences did rift affect the cooling of the soil, since no difference was observed between the ski slope and the natural snow cover. This might be because cold periods were rare and short and thus any snowpack could protect the soil from freezing. The major impact of the ski-slope grooming was a 4 week delay in snowmelt and soil warming at the end of the season. The newly implemented option proved to be a useful strategy for simulating the snowpack of a ski slope. However, snow density was underestimated by the model as it could not account adequately for compaction due to grooming traffic. Our study demonstrates that there is no site-independent answer as to whether a groomed snowpack affects the thermal conditions in the soil.
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