Altered energy flow pathways in a lake ecosystem following manipulation of fish community structure     

Jari Syväranta  Pia Högmander  Tapio Keskinen  Juha Karjalainen  Roger I. Jones 《Aquatic Sciences - Research Across Boundaries》2011,73(1):79-89

We used carbon and nitrogen stable isotope analyses to assess the relative contributions from pelagic and littoral energy sources to higher trophic levels in a lake ecosystem before and after a major food web perturbation. The food web structure of the lake was altered when the population sizes of the most abundant fish species (small perch, roach and bream) were reduced during an attempt to improve water quality by biomanipulation. Fish removal was followed by dense year classes of young fish, which subsequently increased the utilisation of pelagic resources. This was reflected as a decrease in relative energy contribution from littoral sources and also led to more distinct pelagic and littoral food chains after fish removal. Community metrics calculated from stable isotope data indicated increased trophic diversity and occupied niche area, and reduced trophic redundancy in the food web. However, only minor changes were observed in fish trophic positions, although roach and pike occupied slightly lower trophic positions after fish removal. Despite the Jyväsjärvi ecosystem becoming more dependent on pelagic energy after fish removals, the littoral energy contribution was still substantial, particularly to certain fish species. Hence, our results support recent arguments for the importance of benthic production in lake ecosystems. More generally, our results illustrate how large-scale perturbations of food web structure can alter energy flow patterns through an entire ecosystem.  相似文献   

The Anthropocene: is there a geomorphological case?     

Antony G. Brown  Stephen Tooth  Richard C. Chiverrell  James Rose  David S. G. Thomas  John Wainwright  Joanna E. Bullard  Varyl R. Thorndycraft  Rolf Aalto  Peter Downs 《地球表面变化过程与地形》2013,38(4):431-434

The ‘Anthropocene’, as used to describe the interval of recent Earth history during which humans have had an ‘overwhelming’ effect on the Earth system, is now being formally considered as a possible new geological Epoch. Such a new geological time interval (possibly equivalent to the Pleistocene Epoch) requires both theoretical justification as well as empirical evidence preserved within the geological record. Since the geological record is driven by geomorphological processes that produce terrestrial and near‐shore stratigraphy, geomorphology has to be an integral part of this consideration. For this reason, the British Society for Geomorphology (BSG) has inaugurated a Fixed Term Working Group to consider this issue and advise the Society on how geomorphologists can engage with debates over the Anthropocene. This ESEX Commentary sets out the initial case for the formalisation of the Anthropocene and a priori considerations in the hope that it will stimulate debate amongst, and involvement by, the geomorphological community in what is a crucial issue for the discipline. The Working Group is now considering the practical aspects of such a formalization including the relative magnitude problem, the boundary problem and the spatial diachrony of ‘anthropogenic geomorphology’. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Toward a sustainable environmental future for the Southeast Asian region: UNU conference held in Indonesia, 6–10 May 1991     

Juha I. Uitto Dr. 《GeoJournal》1991,24(4):427-428

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Water wars? Geographical perspectives: introduction   总被引：1，自引：0，他引：1  

Juha I. Uitto  & Aaron T Wolf 《The Geographical journal》2002,168(4):289-292

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Cosmogenic Be dating of the Salpausselkä I Moraine in southwestern Finland     

Vincent R. Rinterknecht  Peter U. Clark  Grant M. Raisbeck  Franoise Yiou  Edward J. Brook  Silvio Tschudi  Juha P. Lunkka 《Quaternary Science Reviews》2004,23(23-24):2283-2289

We determined in situ cosmogenic ¹⁰Be ages for nine boulders sampled on the Salpausselkä I (Ss I) Moraine. Previous dating of this moraine indicated that it formed during the Younger Dryas Stadial along the southern margin of the Scandinavian Ice Sheet in southern Finland. Our new exposure ages range from 10.9±1.0 to 13.5±1.2 ¹⁰Be ka, with an error-weighted mean age of 12.4±0.7 ¹⁰Be ka. Our results confirm four previous ¹⁰Be ages obtained 40 km northeast of our sample location. The combined data (n=13) indicate that retreat from the Ss I Moraine occurred at 12.5±0.7 ¹⁰Be ka, in excellent agreement with an age of 12.1 ka for retreat from the Ss I Moraine based on varve chronologies. These results identify the Ss I Moraine as among the best-dated margins associated with Late Quaternary ice sheets.  相似文献   

Bidirectional reflectance spectrometry of gravel at the Sjökulla test field     

Jouni I. Peltoniemi  Jukka Piironen  Jyri Nrnen  Juha Suomalainen  Risto Kuittinen  Lauri Markelin  Eija Honkavaara 《ISPRS Journal of Photogrammetry and Remote Sensing》2007,62(6):434-446

The Sjökulla test site is used for testing and calibrating aerial images. The permanent test field is made of four types of gravel (dark gabbro, grey granite, red granite, white limestone) in two sizes (diameters 8–16 mm and 4–8 mm) set in various patterns. The bidirectional reflection properties of the targets together with their temporal changes must be known in order to carry out radiometric and spectral evaluation and calibration.The bidirectional reflectance distribution functions (BRF) of the gravel have been measured several times in the test fields using portable field goniospectrometers belonging Finnish Geodetic Institute (FGI), and once using the European Goniometic Facility (EGO) of the Joint Research Centre (JRC) at Ispra, Italy. Detailed BRFs have been obtained, showing features typical to particulate media, e.g. a small bowl shape, strong backscattering, and smooth wavelength dependence. Temporal range measurements over several years show that the black gabbro and red granite are fairly stable, while the grey granite has changed somewhat over the years and the white limestone has experienced dramatic darkening effects, requiring action to be taken.The measured BRF data have increased the usability of the test field considerably. The results are also useful in the development and validation of scattering models for particulate media. The site has proved to be a good test bench for goniospectrometric instruments, too.  相似文献   

Social ties and concern for global warming     

Juha V. A. Itkonen 《Climatic change》2015,132(2):173-192

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Finite element seepage flow nets     

J. Aalto 《国际地质力学数值与分析法杂志》1984,8(3):297-303

A variational principle and the corresponding finite element equations for determination of the stream function for soil seepage problems is given using the standard finite element potential solution as data. The procedure is very simple and independent of the element type employed. Generalization of the method to multiply connected domains is included.  相似文献   

Nudging the Impasse? Lessons From the Nationwide Online Wolf Management Forum in Finland     

Matti Salo  Juha Hiedanpää  Mikael Luoma  Jani Pellikka 《社会与自然资源》2017,30(9):1141-1157

During the early 2010s, Finnish wolf (Canis lupus) policy reached an impasse. Unfavorable conservation status, intensifying wolf–human conflict, civil disobedience, legislative confusion, and administrative frustration characterized the situation. As part of a participatory updating process for the Finnish national wolf management plan in 2014, we organized a nationwide wolf management forum to explore how e-participation could be used to nurture deliberation for improved wolf policy. We present our interactive method and the resulting wolf territory-based solutions to the wolf problems that the participants of a nationwide online forum identified. The theoretical and practical significance of our work is that we ascribe value to the functional features of these solutions as modifications to the action environment, shared by people and wolves. In this vein, we discuss the role of e-deliberation on the path toward an institutional fit, and we consider how local decision making could help to implement promising wolf territory-level policy interventions.  相似文献   

Range and AGC normalization in airborne discrete-return LiDAR intensity data for forest canopies   总被引：1，自引：0，他引：1  

Ilkka Korpela  Hans Ole Ørka  Juha Hyyppä  Ville Heikkinen  Timo Tokola 《ISPRS Journal of Photogrammetry and Remote Sensing》2010,65(4):369-379

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