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Petri K.E. Pellikka Milla Lötjönen Mika Siljander Luc Lens 《International Journal of Applied Earth Observation and Geoinformation》2009
We studied changes in area and species composition of six indigenous forest fragments in the Taita Hills, Kenya using 1955 and 1995 aerial photography with 2004 airborne digital camera mosaics. The study area is part of Eastern Arc Mountains, a global biodiversity hot spot that boasts an outstanding diversity of flora and fauna and a high level of endemism. While a total of 260 ha (50%) of indigenous tropical cloud forest was lost to agriculture and bushland between 1955 and 2004, large-scale planting of exotic pines, eucalyptus, grevillea, black wattle and cypress on barren land during the same period resulted in a balanced total forest area. In the Taita Hills, like in other Afrotropical forests, indigenous forest loss may adversely affect ecosystem services. 相似文献
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Various finite element families for the Brinkman flow (or Stokes–Darcy flow) are tested numerically. Particularly, the effect
of small permeability is studied. The tested finite elements are the MINI element, the Taylor–Hood element, and the stabilized
equal order methods. The numerical tests include both a priori analysis and adaptive methods. 相似文献
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Conditional probability of icing in correlation with local weather elements, as well as with different macrocirculation types are investigated on the basis of 23 years of daily observations for two stations situated in the Pannonian Plain (Debrecen) and in mountainous region (Kékestetö, 1000 m above sea-level). Empirical histograms are calculated and a theoretical model of the distribution is elaborated. Ice is generally twice as frequent at night as during the day. Icing is 5–6 times as frequent on the top of the hill as on the plain, especially considering larger water-contents. Macrosynoptic conditions favourable for icing are essentially different in the two circumstances. At the higher altitude icing is more frequent in cyclonic situations. Considerable load is often accompanied with southwesterly, southerly currents. On the plain station however the anticyclonic situations are somewhat more frequently accompanied with ice formation. Wind speed is practically indifferent at the top of the hill, but on the plain ice formation prefers low wind speeds. These differences are in coincidence with the a priori information of the different nature of ice load. Namely, at the top of hill in-cloud icing is the predominant form, while on the plain fine rime and frozen precipitation represent the overwhelming majority of ice load events. No clear differences in probabilities of icing in any of the above relations appear, however, between the two perpendicular directions of measuring devices. From among the possible applications of the results, a local scenario on ice load changes assuming a 0.5 K global warming is presented. 相似文献
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Bitner-Gregersen Elzbieta M. Gramstad Odin Magnusson Anne Karin Malila Mika Petteri 《Ocean Dynamics》2021,71(1):81-95
Ocean Dynamics - Wave field data are affected not only by the accuracy of instruments recording them but also by sampling variability, an uncertainty due to the limited number of observations. For... 相似文献
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Juha E. P. Heikkinen Marja Maljanen Mika Aurela Ken J. Hargreaves Pertti J. Martikainen 《Polar research》2002,21(1):49-62
We studied carbon dynamics on various surface parts of a highly patterned fen, typical in northern Finland, to examine the importance of different microsites to the areal carbon fluxes. The studies were carried out in June-September 1995 on a mesotrophic flark fen (an aapa mire) in Kaamanen (69°08'N, 27° 17'E). Wet flarks, moist lawns and dry strings accounted for 60%, 10% and 30% of the surface area, respectively. A static chamber technique was applied to measure the CH4 exchange, the instantaneous net ecosystem exchange (NEE, transparent chamber) and the ecosystem respiration (Rtot' opaque chamber) in several microsites. The static chamber results were compared with those obtained by the eddy covariance technique. The mean daytime areal net ecosystem CO2 exchange rate measurement in conditions where photosynthesis was light saturated (PAR>400 μmol m-2 s-1 ) varied during the measurement period from −59 mg CO2 -C m−2 h−1 (release) to 250 (uptake). The mean CH4 emission during the measuring period was 78 mg CH4- Cm−2 d−1 on the flarks, 68 mg on the lawn and 6.0 mg on the strings. The strings without shrubs (mainly Betula nana ) were in general net sources of CO2 , even during the middle of the growing season, whereas the lawns, flarks and also strings growing B. nana showed a daytime net uptake of CO2 . Areally integrated chamber results showed lower CO2 and higher CH4 fluxes than predicted from the eddy covariance measurements. 相似文献
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The degradation of organic wastes and the corrosion of metallic wastes and steel containers in low and intermediate level radioactive waste (LLW/ILW) repositories are important processes that affect repository geochemistry and the speciation and transport of radionuclides. Gas is generated in association with these degradation processes and this has the potential to overpressure the repository, which can promote transport of groundwater and gas, and consequently radionuclide transport. Microbial activity plays an important role in organic degradation, corrosion and gas generation through the mediation of reduction–oxidation reactions. 相似文献