1,720,982 research outputs found
Beach sand as a biofilter: enzymatic activity and organic matter relationships in oligotrophic sites differently influenced by anthropogenic pressures and morphodynamism
No full textSandy beaches provide a number of ecosystem services, such as the breakdown of organic matter (OM), nutrient mineralisation and water filtration. These environments may be considered as biofilters, able to regulate the transport and transformation of OM from land to sea and vice-versa, due to the porous structure of the sediment and the colonisation by microorganisms. The efficiency of OM recycling performed by enzymatic activities (EAs) was evaluated in three beaches of the NW Mediterranean Sea, characterised by different anthropogenic pressure (urbanisation), and morphodynamic characteristics (exposition to waves). The sampling was focused on the area that includes the swash zone and the wet emerged beach. Urbanisation significantly influenced EAs, leading to a decoupling between the lipolytic EAs and the lipid content of sediment. Natural and anthropogenic lipids, showing higher turnover times than other OM (proteins), accumulated in the sediment, notwithstanding the very high lipolytic activities. In the sheltered side of the urbanised sites, significant correlations between EAs, sedimentary OM and seawater inorganic nutrients were recorded, confirming the biofilter activity. In the exposed sites, the wave action increased the exchanges with the sea by water flushing inside the sediment, and EAs were related mainly to salinity. Especially in the least urbanised beach, coarse texture, higher pendency and heterogeneity of the sediment decreased the biofilter activity, allowing photosynthetic producers to increase their biomass. In this case, the beach hosted production of fresh OM, contributing to fulfil the trophic web requirements
Development of marine biofilm on plastic: ecological features in different seasons, temperatures, and light regimes
No full textMicroorganisms are able to colonise abiotic surfaces in marine waters, supporting ecological and biogeochemical functions. In turn, environmental factors may determine the accrual and activity of microbial biofilms. The environment is subject to global climate change and pollution by plastic, and therefore we focused on the response of natural marine biofilm on common plastic items (bottles) to seasonality, increases in temperature, and light regime in experimental systems. Chlorophyll-a, prokaryotic abundance and replication frequency, organic matter (OM), and enzymatic activity were measured. Statistical analysis indicated that different environmental conditions modified the biofilms. Summer conditions favoured photoautotrophic organisms. The increase of photoautotrophic biomass could have caused the prokaryotic microorganisms’ lowest abundances. Temperature rise affected chlorophyll-a and increased hydrolytic activities, responsible for OM degradation, as also recorded in the absence of light. In winter, temperature variation led to a delayed increase of enzymatic activity, suggesting the need for a time lag to potentiate OM recycling. The correlations between prokaryotic abundance and the other variables highlighted tighter links in cases of temperature alteration. Our results indicated that a potential temperature increase, and light limitation due to plastic sinking in the water column, could modify the biofilm community, increasing the role of prokaryotic organisms
Meteorological and climatic variability influences anthropogenic microparticle content in the stomach of the European anchovy Engraulis encrasicolus
No full textMeteorological and climatic phenomena affect oceanographic characteristics and, consequently, anthropogenic microparticle aggregation. The same phenomena influence the ecology of pelagic fish, but whether there is a connection between meteorological and climatic characteristics and microparticle ingestion remains unknown. In the NW Mediterranean during the springs of 2011–2014, the incidence of contaminated European anchovies (35 ± 17%) and microparticle abundance in the stomach content (0.46 ± 0.25 microparticles ind−1) may have owed to higher concentrations of microparticles due to hydrodynamism. Year 2011 showed a higher fragment contribution (60 ± 17%). The statistical analysis indicated a link between fragment abundance and climatic characteristics, with low North Atlantic Oscillation index values for the previous cold season indicating the transport of water from the polluted Tyrrhenian Sea. Low-density microplastic (polyethylene and polypropylene) was found, a selection due to the pelagic behaviour of anchovy. Fibre abundance remained quite constant throughout the 4-year period, pointing to diffused input not dependent on meteorological forcing. In 2012, anchovies were subjected to bottom-up limitation, due to adverse meteorological forcing (high early spring temperatures, low rainfall). The anchovies mainly ingested fibres through less energy-expensive filter-feeding. Therefore, meteorological and climatic forcing regulates microparticle intake by fish and should be considered for pollution mitigation
Relationship between ectoenzymatic activity and availability of organic substrates (Ross Sea, Antarctica): An experimental approach
No full textOrganic matter consumption and decomposition were studied in four experimental systems, having collected different organic substrates in the Ross Sea in December 1994. For the experimental approach selected, processes normally acting on a mixed pool of substances could be separated and the main features of each phenomenon could be focused on. Through the strict relationship between each experimental system and natural conditions shown by organic matter assessment, ectoenzymatic activity trends and their relation with Antarctic water substrates could be described. Through ice melting the water column becomes rich in large pools of substrates, as well as enzyme-producing micro-organisms, capable of quick development. The quantitative predominance of leucine-aminopeptidase throughout the year is well known, but its relative importance seems to decrease when, owing to production events, the environment is enriched with autotrophic- and heterotrophic-derived substances, leading to glycolytic enzymes expression. Thus, ectoenzymatic activity is supposed to be one of the factors responsible for organic matter variations, showing quantitative and qualitative changes depending on substrate availability
Decomposition of fecal matter and somatic tissue of Mytilus-Galloprovincialis - changes in organic-matter composition and microbial succession
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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
Particulate organic matter composition in a semi-enclosed Periantarctic system: the Straits of Magellan
Full text linkSUMMARY: The elemental and biochemical composition of particulate organic matter (POM) was investigated in the Straits of Magellan during February-March 1991. Twenty-two stations were selected in order to identify different areas of the Magellan ecosystem from a trophic point of view. The Strait of Magellan can be divided into three subsystems charac-terized by different hydrological and geomorphological conditions. Seston concentrations were mostly constrained by phys-ical events, particularly the influence of oceanic and land run-off water inputs and the strong vertical mixing and resuspen-sion events. POM composition displayed quali-quantitative differences between the three areas. In the first subsystem, influ-enced by Pacific waters, the low seston and POM concentrations and the high POC/Chl-a ratio values indicated the gener-al predominance of the detrital and heterotrophic fractions. In the second subsystem, characterized by superficial stratifica-tion, higher seston and organic matter concentrations and lower values of POC/Chl-a ratio were found, indicating that this subsystem was influenced by an active autotrophic component. Shallow waters with intense tidal regime and strong verti-cal mixing characterized the third subsystem, connected to the Atlantic Ocean, which displayed an increasing importance of the inorganic fraction (values of the POC/TSM ratio lower than in the other systems). Moreover, the third subsystem showed higher values of the RNA/DNA ratio, possibly indicating that resuspension events may enhance the metabolic state of th
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