1,721,014 research outputs found
The zooplankton population of a small alpine lake: Lake Malghette (Trentino, Italy)
No full textThe zooplankton population of Lake Malghette (1891 m asl) was surveyed in 1994-1995. The zooplankton of this small oligotrophic lake included the copepods Cyclops abyssorum-tatricus, Acnathodiaptomus denticornus, the cladocerans Holopedium gibberum, Daphnia gr longispina, and the rotifer Kellikottia longispina
Congruence between molecular and morphological systematics of Alpine non-biting midges (Chironomidae, Diamesinae)
No full textIn mountain regions, climate change is resulting in glacial retreat, causing biodiversity loss in glacial-fed streams (kryal habitat). Diamesa species (Diptera Chironomidae), the main colonizers of the kryal in the Alps, are the aquatic insects more threatened by extinction. In recent years, DNA barcoding was successfully adopted to delimit species of chironomids and provided species identification. We highlighted that for the Diamesa genus, inconsistencies remain between identification on a morphological and molecular basis, mainly within cinerella and zernyi groups, raising doubts about the validity of head colour as a good diagnostic taxonomic character. Molecular phylogeny reconstruction based on mitochondrial (cytochrome oxidase subunits I and II) and one nuclear (ribosomal 18S rRNA) markers revealed that D. bohemani and D. zernyi on one hand, and D. cinerella and D. tonsa on the other hand, represent populations of the same species. Divergence times suggested that the radiation of these alpine species seems to have been driven by the climatic events with the alternation of glacial periods that happened in the Pliocene and Pleistocene. The initial separation of the oriental species D. steinboecki seems to be due to the tectonic movements of the Periadriatic fault system that probably favoured the emergence of lakes and streams, successively colonized by D. steinboecki. This study raises important concerns, from the validity of diagnostic characters used today to identify larval types up to the uncertainty about how many species of Diamesa inhabit the European Alps and what their fate will be within the scenario of climate change
Relative importance of space and time in determining the biotic structure in the upper part of spring-fed streams
No full textAn increasing number of recent investigations of a wide range of species have considerably changed perspectives in spring ecology. However, relatively little is known about the differences between the eucrenon and assemblages in downstream habitats. We studied changes in environmental conditions and in 4 taxonomic groups along a downstream continuum. Assemblages of diatoms, other benthic macroalgae including cyanobacteria, macroinvertebrates, and bryophytes were compared among eucrenal, hypocrenal, and epirhithral stations in 2 spring-fed streams of the southeastern Italian Alps. Environmental factors were less variable at the eucrenal station than at downstream stations, but this pattern was not reflected by an equivalent response of biotic assemblages. The eucrenon clearly differed from assemblages at downstream stations in ways that varied between taxonomic groups and time. Diatom and macroinvertebrate assemblage compositions were more variable at the eucrenal station than at downstream stations. Space was a more important factor than time for diatoms and benthic macroalgae, whereas space and time were almost equally important for macroinvertebrates. Downstream changes were inconsistent between taxonomic groups, and a larger number of spring-fed streams must be studied to detect more generally valid patterns in downstream variation of different taxonomic groups. © 2012 The Society for Freshwater Science
Comparison between natural and impacted Alpine lakes six years after hydropower exploitation has ceased
No full textMany lakes in mountain regions have been used for hydropower generation since the 1950s. It has been estimated that as many as 79% of the rivers in the Alps have been affected by the presence of hydropower plants. In this context, the shutting down of hydropower plants on a group of Alpine lakes represented a good opportunity to study the ecological impact on them. We selected nine lakes that had been affected and nine that had not, and analysed the differences in environment, littoral diatoms and zoobenthos, phytoplankton, zooplankton, and fish. Results showed that benthic biota -diatoms and zoobenthos- were the most affected by water-level drawdown during winter months. Even six years after the end of hydroelectric operations, diatom species richness and diversity were lower in impacted lakes. Assemblage structure was different for both diatoms and zoobenthos. Phytoplankton and zooplankton were similar in impacted and unaffected lakes in terms of both species richness (and diversity) and assemblage structure. The degree of impact on fish was unclear because illegal stocking of lakes with allochthonous fish species had taken place. This study showed that compared to limnetic biota, littoral communities were the most affected by the decrease in water volume every winter. Six years after the end of hydroelectric operations, diatoms, and to lesser extent zoobenthos, were still different compared to those in natural (unaffected) lakes. Planktic communities seem to be either more resistant to the disturbances, or else able to recover more quickly to their former condition
Comparison between natural and impacted Alpine lakes six years after hydropower exploitation has ceased
No full textMany lakes in mountain regions have been used for hydropower generation since the 1950s. It has been estimated
that as many as 79% of the rivers in the Alps have been affected by the presence of hydropower plants. In this context,
the shutting down of hydropower plants on a group of Alpine lakes represented a good opportunity to study the ecological
impact on them. We selected nine lakes that had been affected and nine that had not, and analysed the differences in
environment, littoral diatoms and zoobenthos, phytoplankton, zooplankton, and fish. Results showed that benthic biota
–diatoms and zoobenthos– were the most affected by water-level drawdown during winter months. Even six years after the
end of hydroelectric operations, diatom species richness and diversity were lower in impacted lakes. Assemblage structure
was different for both diatoms and zoobenthos. Phytoplankton and zooplankton were similar in impacted and unaffected
lakes in terms of both species richness (and diversity) and assemblage structure. The degree of impact on fish was unclear
because illegal stocking of lakes with allochthonous fish species had taken place. This study showed that compared to
limnetic biota, littoral communities were the most affected by the decrease in water volume every winter. Six years after the
end of hydroelectric operations, diatoms, and to lesser extent zoobenthos, were still different compared to those in natural
(unaffected) lakes. Planktic communities seem to be either more resistant to the disturbances, or else able to recover more
quickly to their former conditio
Headwaters’ Isotopic Signature as a Tracer of Stream Origins and Climatic Anomalies: Evidence from the Italian Alps in Summer 2018
No full textGlaciers are shrinking due to global warming, resulting in a diminishing contribution of ice and snowmelt to headwaters and subsequent consequences to freshwater ecosystems. Within this context, we tested whether water-stable isotopes are spatio-temporal tracers of (i) water in high altitude periglacial environments, being the isotopic signature of surface water inherited from the snow/icemelt, groundwater, and rainfall; and (ii) regional (year-specific) meteorological conditions, being the isotopic signature of precipitations affected by air temperature, humidity and aqueous vapour origin, ascribing stable isotopes to the list of "essential climate variables" (ECVs). To this end, we investigated the ionic and isotopic composition (δ18O and δ2H) of six high-altitude streams and one pond in the Italian Alps (Noce and Sarca basins) during the ablation season in 2018. Differences between habitat types (pond, kryal, rhithral, krenal) were detected. More negative values of δ18O and δ2H were recorded in the kryal and glacio-rhithral sites, dominated by ice and snowmelt, in early summer. Less negative values were recorded in these sites in late summer, as well as in the krenal sites, which were dominated by groundwater and rainfall inputs. The isotopic results also show that the complex alpine orography influences air masses and moisture, ultimately resulting in isotopic differences in the precipitations of neighboring but distinct catchments (Sarca and Noce basins). On average, less negative values were recorded in the Sarca basin, characterized by a higher contribution of precipitation of Mediterranean origin. In general, isotopic results of the entire water population appeared to be strongly influenced by the regional climatic anomaly of 2018, which was anomalously warm. Therefore, the study will provide additional information for the climate change debate, proposing water isotopes as ECVs for assessing change in a warmer future
Respiration rate and oxy-regulatory capacity in cold stenothermal chironomids
No full textThe effects of temperature and oxygen saturation on the respiration rate of two cold stenothermal chironomids, Diamesa insignipes and Pseudodiamesa branickii were investigated. Fourth instar larvae were collected in winter in a glacio-rhithral stream (1300 m a.s.l., Alps, NE-Italy) and their respiration rate was measured with a Clark's electrode in the range 0–14 °C. The respiration rate was significantly higher in D. insignipes than in P. branickii at low temperatures (≤4 °C), higher in P. branickii between 8 and 12 °C and comparable at 14 °C. Higher values of R (regulation value), R25% (respiration rate at 25% oxygen saturation) and b1/b2 (slope ratio in piecewise linear regression), and lower values of Pc (critical pressure) and I (initial decrease) were recorded in P. branickii than in D. insignipes. These values are compatible with oxy-regulatory behaviour in P. branickii, whereas D. insignipes appeared to be almost an oxy-conformer. On the basis of this autoecological information, new implications regarding survival of species from cold, high altitude habitats under changing climatic conditions are made
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
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