Stratification of selected hydrolytic enzyme activities in the sediment in two lakes in Finland     

Mika A.KHKNEN  Risto HAKULINEN 《国际泥沙研究》2012,27(2):250-258

To investigate the stratification of hydrolytic enzyme activities and importance of subsurface layers in depolymerization of detritus biopolymers,nine hydrolytic enzyme activities involved in the cycling of carbon,phosphorus,nitrogen and sulphur were measured in various sediment layers and their extracts at Kylaniemi in Lake Saimaa in southern Finland and in Lake Ahvenjarvi in northern Finland. The results show that for each lake all nine hydrolytic enzyme activities were higher in all sediment layers than in comparable sediment extracts indicating that the major part of enzymes was bound to the sediment particles in all layers in both lakes.Carbohydratase,P-cellobiosidase,activities did not show any gradient with sediment depth at Kylaniemi in Lake Saimaa indicating that there was rapid turnover of carbohydrates in the entire sediment column.The activities of acetate esterase,butyrate esterase,phosphomonoesterase,aminopeptidase,N-acetyl glucosaminidase,sulphatase andβ-glucosidase in the deepest layers were 19-53%of those in the surface sediment indicating that depolymerization of biopolymers involved in the cycling of carbon,nitrogen,phosphorus and sulphur was substantial in subsurface sediment.  相似文献   

Characterising the origin,nature and fate of sediment exported from catchments perturbed by active tectonics   总被引：1，自引：1，他引：0  

Alexander C. Whittaker  Mikaël Attal  Philip A. Allen 《Basin Research》2010,22(6):809-828

Changes to the tectonic boundary conditions governing erosional dynamics in upland catchments have a significant effect on the nature and magnitude of sediment supply to neighbouring basins. While these links have been explored in detail by numerical models of landscape evolution, there has been relatively little work to quantify the timing, characteristics and locus of sediment release from upland catchments in response to changing tectonic boundary conditions that are well‐constrained independently. We address this challenge by quantifying the volume and granulometric characteristics of sediment exported from modern rivers draining across active normal faults in the Central Apennines in Italy. We demonstrate that catchments undergoing a transient response to tectonics are associated with significant volumetric export of material derived primarily from the zone upstream of the fault, producing bi‐modal grain‐size distributions with elevated D₈₄ values within the transient reach. This is in direct contrast to the headwaters, where the fluvial capacity to transport sediment is low and the grain‐size distribution of material in transit is fine and uni‐modal. The grain‐size response is driven by landslides feeding coarse material directly into the channel, and we show the amplitude of the signal is modulated by the degree of tectonic perturbation, once the threshold for bedrock landsliding is exceeded. Additionally, we evaluate the length‐scale over which this transient grain‐size signal propagates downstream into the basin. We show that the coarse‐fraction sediment released is retained in the proximal hanging‐wall if rates of tectonic subsidence are high and if the axial river system is small or far from the fault‐bounded mountain front. Our results therefore provide some of the first quantitative data to evaluate how transient landscape responses affect the locus, magnitude and calibre of sediment supply to basins.  相似文献   

Hydrogeochemical Processes Controlling the Water Chemistry of a Closed Saline Lake Located in Sahara Desert: Lake Qarun,Egypt   总被引：1，自引：0，他引：1  

Mahmoud S. M. Abdel Wahed  Essam A. Mohamed  Mohamed I. El-Sayed  Adel M’nif  Mika Sillanpää 《Aquatic Geochemistry》2015,21(1):31-57

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Computations with finite element methods for the Brinkman problem     

Antti Hannukainen  Mika Juntunen  Rolf Stenberg 《Computational Geosciences》2011,15(1):155-166

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   

Extreme wave events and sampling variability     

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   

Experimental and modelling investigations of the biogeochemistry of gas production from low and intermediate level radioactive waste     

Joe Small  Mikko Nykyri  Mika Helin  Ulla Hovi  Tuija Sarlin  Merja Itävaara 《Applied Geochemistry》2008

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   

Evolution of fibrils with special reference to flare activity     

Katsuo Tanaka 《Solar physics》1976,47(1):247-259

We show observational results on the pre-flare evolutions of H structures as well as the developments of H flares. It is shown that the chromospheric features are brought to a sheared state before flares due to motions of footpoints which correspond to particular sunspot motions. Generally in evolutions of the chromospheric features it is found that motions and reconnections of the footpoints play essential roles. The following three stages are found for development of the neutral line filament before flares: (1) formation of a filament as a result of reconnection; (2) increase of the shear of the filament due to the shear motion; and (3) reconnection of fine components of the filament to form an elongated component immediately before flares. We further show developments of two particular flares with and without the filament, and point out basic release processes of flares. The flare that occurred at the filament (July 5, 1974) started with the activation of the elongated component of the filament after the process (3). The main phase of a two-ribbon flare is considered as the rises of short components of the filament triggered by the rising motion of the elongated component. The flare of September 10, 1974 occurred at the region where fibrils connect the sunspots in distorted form. Pre-flare distortion was produced by translational rotation of the sunspot. Development of this two-ribbon flare is interpreted as being due to successive rises of the fibrils with a self-trigger mechanism.On leave from Tokyo Astronomical Observatory (present address).  相似文献   

Spatial feeding patterns of herring (Clupea harengus L.), sprat (Sprattus sprattus L.), and the three-spined stickleback (Gasterosteus aculeatus L.) in the Gulf of Finland, Baltic Sea     

Peltonen  Heikki; Vinni  Mika; Lappalainen  Antti; Ponni  Jukka 《ICES Journal of Marine Science》2004,61(6):966-971

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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   

Correlation of ice load with large-scale and local meteorological conditions in Hungary     

J. Mika  T. Szentimrey  M. Csomor  Z. Kvr  C. Nemes  P. Domonkos 《Atmospheric Research》1995,36(3-4)

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