1,721,123 research outputs found
Restoration of riverine habitat for fishes - analyses of changes in physical habitat conditions
Full text linkAbstractThe subject of the study was to search and test restoration measures for the most common physical habitat degradations in Finnish rivers.Methods for constructing nursery and spawning habitats for salmonid fishes were tested in small rivers dredged for timber floating in the Iijoki watercourse. Physical habitat modelling was used to simulate the effects of restoration measures to the hydro-physical conditions and potential fish habitats. The rehabilitation of the river bed and the placement of boulder structures, especially large boulder dams, made the rapids spatially more complex and increased the availability of potential physical habitat for brown trout (Salmo trutta).The physical habitat model was applied in the river Siikajoki to estimate the impacts of flow regulation patterns on the physical habitat quality. No single flow event causing a bottle-neck effect on the potential habitat suitable for brown trout was found. In a sensitivity analysis of habitat modelling, modifications of the suitability criteria appeared to have a major influence on habitat suitability for young brown trout.The applicability of low reefs and narrow side channels for fish habitat improvement was studied, using the large river impoundment of Oulujoki as a test area. Limited validation experiments of the model results were carried out on the basis of fish telemetry experiments and observations by local rod fishermen. The restoration measures appeared to diversify the channel structure and increase sheltered lateral habitats for grayling (Thymallus thymallus).Habitat structure and fish populations of seven small forest streams and two modified streams were surveyed using visual evaluation and electrofishing studies. None of the studied streams was found to be in pristine condition in all of its reaches. Brown trout was the most abundant species in most of the study streams. In most streams the brown trout distribution correlated positively with substrate size. The accumulation of fine materials on the stream bottom due to forestry operations was estimated to be the most harmful human impact on the studied streams. Some restoration suggestions were made for each of the streams.Academic Dissertation to be presented with the assent of the Faculty of Technology, University of Oulu, for public discussion in Raahensali (Auditorium L10), Linnanmaa, on October 31th, 2003, at 12 noon.Abstract
The subject of the study was to search and test restoration measures for the most common physical habitat degradations in Finnish rivers.
Methods for constructing nursery and spawning habitats for salmonid fishes were tested in small rivers dredged for timber floating in the Iijoki watercourse. Physical habitat modelling was used to simulate the effects of restoration measures to the hydro-physical conditions and potential fish habitats. The rehabilitation of the river bed and the placement of boulder structures, especially large boulder dams, made the rapids spatially more complex and increased the availability of potential physical habitat for brown trout (Salmo trutta).
The physical habitat model was applied in the river Siikajoki to estimate the impacts of flow regulation patterns on the physical habitat quality. No single flow event causing a bottle-neck effect on the potential habitat suitable for brown trout was found. In a sensitivity analysis of habitat modelling, modifications of the suitability criteria appeared to have a major influence on habitat suitability for young brown trout.
The applicability of low reefs and narrow side channels for fish habitat improvement was studied, using the large river impoundment of Oulujoki as a test area. Limited validation experiments of the model results were carried out on the basis of fish telemetry experiments and observations by local rod fishermen. The restoration measures appeared to diversify the channel structure and increase sheltered lateral habitats for grayling (Thymallus thymallus).
Habitat structure and fish populations of seven small forest streams and two modified streams were surveyed using visual evaluation and electrofishing studies. None of the studied streams was found to be in pristine condition in all of its reaches. Brown trout was the most abundant species in most of the study streams. In most streams the brown trout distribution correlated positively with substrate size. The accumulation of fine materials on the stream bottom due to forestry operations was estimated to be the most harmful human impact on the studied streams. Some restoration suggestions were made for each of the streams
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Patterns in northern stream guilds and communities
No full textPatterns in northern stream communities are not yet well understood. Here, I document spatial patterns in predator-prey relationships and patterns in community structure of semi-sessile stream insects and stream bryophytes in northeastern Finland. Spatial distribution of predatory stoneflies was generally random, whereas caddisfly predators (Rhyacophila spp.) were aggregated to areas of highest density of larval black flies. After the emergence of black flies, the distribution of R. obliterata became random. The analysis of mapped point patterns proved more robust in detecting scales of predator-prey interaction than more conventional sampling techniques. Ontogenetic niche shifts in the microhabitat use by filter-feeding caddis larvae were detected in all five species studied. In particular, 5th instar larvae were clearly separated from the younger larval stages, irrespective of species. Ontogenetic niche shifts are probably nearly universal among benthic insects, and should be considered in any study of lotic insect community structure. It is further suggested that coexistence in the guild of filter-feeding caddis larvae is facilitated by independent aggregation of species to patchily distributed resources. Occurrence of stream bryophytes was strongly associated with the disturbance history (substratum movement, water level fluctuation) of a site. In the absence of disturbance, a few tall perennials (e.g. Fontinalis spp.), were able to monopolize space. Frequently disturbed habitats in large rivers were characterized by low-statured shuttle species, which either possess a high capacity for propagule dispersal or are able to withstand frequent scouring of substratum. In streams, small-scale disturbances leave patches open for colonization by facultatively aquatic species which tolerate both submersed and stranded conditions.unknown accessibilityei tietoa saavutettavuudest
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
The impact of anthropogenic channel alteration on the Retention of Particulate Organic Matter (POM) in the third-order river Ilm, Germany
Full text linkThis paper describes new, easy to handle, liquid nitrogen sampler for the upper layer (80-160 mm) of water sediment and associated benthic organismus in streams and lakes up to 1.2 m depth. The 0.0531 m2 sediment sample keeps its natural composition and spatial structure. The 15 kg total weight of the two sampler components enables use by hand even in not easily accessible rural areas. A successful two year test period in several first and second order streams demonstrated the applicability of sampler for sediment textures from fine clay to cobbles and velocity up to 1 m s-1
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