Carbon dioxide and methane dynamics in a sub-Arctic peatland in northern Finland   总被引：1，自引：0，他引：1  

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 (R_tot' 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⁻²h⁻¹ (release) to 250 (uptake). The mean CH₄ emission during the measuring period was 78 mg CH_4-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   

Geometry of spinor regularization     

David Hestenes  Pertti Lounesto 《Celestial Mechanics and Dynamical Astronomy》1983,30(2):171-179

The Kustaanheimo theory of spinor regularization is given a new formulation in terms of geometric algebra. The Kustaanheimo-Stiefel matrix and its subsidiary condition are put in a spinor form directly related to the geometry of the orbit in physical space. A physically significant alternative to the KS subsidiary condition is discussed. Derivations are carried out without using coordinates.  相似文献   

Impact of peatland drainage and restoration on esker groundwater resources: modeling future scenarios for management   总被引：1，自引：0，他引：1  

Pekka M. Rossi  Pertti Ala-aho  John Doherty  Bjørn Kløve 《Hydrogeology Journal》2014,22(5):1131-1145

Esker aquifers are common groundwater bodies in Europe. Management of these aquifers should take account of the sustainability of groundwater-dependent ecosystems and land use in an integrated way. An unconfined esker aquifer in northern Finland was modelled with MODFLOW to determine how groundwater resources are impacted by the surrounding peatland drainage scheme and to simulate scenarios for possible drainage restoration. The impacts of groundwater abstraction and climate change were also simulated. A calibration-constrained Monte Carlo method was used to provide information on the uncertainties associated with model predictions. The results suggest that peatland drainage in the vicinity of eskers can have a significant role in lowering the water table, even though climate variability may mask these impacts. Drainage restoration by filling the ditches might have positive impacts on the aquifer water levels. Comparison of water-table changes caused by peatland drainage with the changes brought by water abstraction and climate variability helped to quantify impacts of different land-use scenarios and facilitated discussion with the local stakeholders. Based on this study, more attention should be devoted to peatland drainage schemes in integrated groundwater management of esker aquifers.  相似文献