1,721,104 research outputs found
Composizione della comunità macrobentonica del Torrente Parma nel tratto appenninico interessato dalla costruzione di un nuovo tracciato stradale
No full textMonitoring of Neotropical Streams Using Macroinvertebrate Communities: Evidence from Honduras
Full text linkAssessing the water quality by using biological indicators is a reliable and economically feasible way to promote environmental conservation in developing tropical countries. Here, we report one of the few examples of river biomonitoring in Honduras. In June 2005, benthic macroinvertebrates were collected from six sites in the Río Cangrejal basin. An adapted version of the Biological Monitoring Working Party index (BMWP) was used to assess the water quality because it is simple, consolidated, relatively easy to use, and needs a family-level identification. Moreover, two other community metrics were calculated, namely the total taxon richness and local contribution to beta diversity (LCBD). Differences in the biomonitoring and diversity metrics among sites and their correlations were statistically tested. Thirty-nine macroinvertebrate taxa were collected and, despite significant differences in the BMWP score, all sampling sites were classified in the high environmental quality class. A very strong and positive correlation between the BMPW and taxon richness was found, while LCBD did not vary significantly and did not correlate with the other metrics. Our results suggest that taxon richness could be used as a surrogate indicator to assess the water quality when consolidate biomonitoring methods are not available
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
Effects of intermittence on Alpine streams ecosystems: hyporheic zone and resilience
No full textOver the last few years, a significant portion of rivers in Northern Italy have been progressively shifting from naturally perennial to intermittent systems, with prolonged dry phases occurring in summer and also in winter . However, the aquatic communities of Alpine rivers lack strategies and adaptations to survive such hydrological and physico-chemical changes. Aim of this study is to explore the impact of intermittence in previously-perennial Alpine stream reaches, considering biodiversity, taxonomic and functional aspects. In detail, we aimed to assess the role of the hyporheic zone in increasing the resilience of these aquatic systems to drought. The hyporheic habitat was monitored in 2017 in two sites (one perennial and one intermittent) in the upper course of the Po River (Val Po, Cuneo province) with piezometers installed in the riverbed, reaching -1 m (both sites) and -3 m depth (intermittent site). Sampling was conducted from July to March 2018 at short time intervals to follow the strongest drought recorded in the area from the 1800s. Sampling was resumed at both stations in January 2018 following the onset of winter precipitations, and conducted at short time intervals during the rewetting phase, and monthly after both stations were permanently submersed. Relative and total abundances of hyporheic and benthic invertebrates changed differently in the two stations during the different phases of the hydrological cycle, suggesting that the hyporheic and benthic communities respond quickly to the onset of the drought. As expected, where water is permanent, the hyporheic communities are abundant; conversely, increasingly harshness (i.e, reduction of the water table) affects hyporheic communities and increases the use of the hyporheic habitat as a refuge by benthic taxa
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
Mini hydro e impatti ambientali sintesi organizzata dello stato dell'arte scientifico
No full textIn conformità con gli obiettivi del progetto Renerfor, la presente relazione intende offrire una sintesi la più possibile ampia e oggettiva dell'attuale stato dell'arte delle ricerche e degli studi relativi al mini idroelettrico e agli impatti ambientali che ad esso possono risultare associat
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
Supraseasonal drought in an Alpine river: Effects on benthic primary production and diatom community
Full text linkOver the last decades, the ongoing global climate change, combined with consequent increasing water demand for human needs, is causing recurrent droughts in previously perennial streams. These phenomena have been dramatically increasing their extent, with significant repercussions on the entire food web. Consequences of water scarcity are particularly remarkable in mountain streams, where the frequency of droughts is increasing at a rate that does not allow species to adapt. In the present research, we monitored benthic diatom communities within an intermittent Alpine river (Pellice River; North-Western Italy) during the three key phases of its hydrological cycle: i) stable flow ii) lentification iii) rewetting of the riverbed after a supraseasonal drought lasting five months. We tested the response of diatom communities in terms of compositional, structural and functional metrics (primary production, species composition, ecological guilds, life forms and eco-morphological groups) hypothesising both taxonomic and functional changes during the different steps of this hydrological cycle. Significant changes in benthic chlorophyll a occurred in the three hydrological phases. In particular, the relative proportion of the chlorophyll a of the three main autotrophic groups inhabiting the periphyton (namely diatoms, cyanobacteria and green algae) resulted as a reliable metric for the evaluation of the hydrological disturbance. Diatom chlorophyll a significantly decreased during both lentification and drought. The three phases were significantly characterized by different species and functional groups. During the stable flow the low profile (i.e., species of short stature, adapted to high current velocities and low nutrients concentrations) was the most representative guild and Achnanthidium pyrenaicum was the most abundant species; this phase was also characterized by the presence of stalked taxa. We observed a significant decrease of high profile species (i.e., species of tall stature, adapted to high nutrients concentrations and low current velocities) during the lentification phase, which was characterized by taxa belonging to the genera Navicula, Nitzschia and Ulnaria. During the rewetting, small and medium sized high profile diatoms as well as motile ones (i.e., fast moving species) characterized the assemblages. Our results showed that the complete recovery of diatom communities took at least 70 days after water return. The rapid and widespread extension of droughts in the Alpine area will have severe consequences on the river biota, also favouring the spread of invasive taxa. For this reason, outlining patterns of diatom response to droughts and detecting reliable metrics for the evaluation of this specific impact is very urgent and important
Contribution of beta diversity in shaping stream macroinvertebrate communities among hydro-ecoregions
No full textRivers are heterogeneous and patchy-structured systems in which regional biodiversity of aquatic communities typically varies as a function of local habitat conditions and spatial gradients. Understanding which environmental and spatial constraints shape the diversity and composition of benthic communities is therefore a pivotal challenge for basic and applied research in river ecology. In this study, benthic invertebrates were collected from 27 sites across three hydro-ecoregions with the aim of investigating patterns in α- and β diversity. We first assessed the contribution to regional biodiversity of different and nested spatial scales, ranging from micro-habitat to hydro-ecoregion. Then, we tested differences in α diversity, taxonomic composition and ecological uniqueness among hydro-ecoregions. Variance partitioning analysis was used to evaluate the mechanistic effects of environmental and spatial variables on the composition of macroinvertebrate communities. Macroinvertebrate diversity was significantly affected by all the spatial scales, with a differential contribution according to the type of metric. Sampling site was the spatial scale that mostly contributed to the total richness, while the micro-habitat level explained the largest proportion of variance in Shannon–Wiener index. We found significant differences in the taxonomic composition, with 39 invertebrate families significantly associated with one or two hydro-ecoregions. However, effects of environmental and spatial controls were context dependent, indicating that the mechanisms that promote beta diversity probably differ among hydro-ecoregions. Evidence for species sorting, due to natural areas and stream order, was observed for macroinvertebrate communities in alpine streams, while spatial and land-use variables played a weak role in other geographical contexts
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