1,721,023 research outputs found
Metodologie di campionamento e andamenti stagionali delle diatomee bentoniche nella laguna di Venezia
No full textDECREMENTO DELLE CONCENTRAZIONI DI FITOPLANCTON E CORRELAZIONI CON LE COMUNITA' MICROBENTONICHE E RILEVANTI VARIABILI AMBIENTALI NELLA PARTE CENTRALE DELLA LAGUNA DI VENEZIA
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DISTRIBUZIONE SPAZIO-TEMPORALE DEL FITOPLANCTON NELL’AREA CENTRALE DELLA LAGUNA DI VENEZIA
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Changes in abundance and composition of phytoplankton and microphytobenthos due to increased sediment fluxes in the Venice lagoon, Italy
No full textBy comparison with measurements carried out in 1990-91, phytoplankton biomass in 1998-99 appears strongly reduced in the central basin of the Venice lagoon. Chlorophyll a concentrations, which in the past easily reached 100 mug dm(-3), reached only 5 mug dm(-3) during this investigation. Phaeopigment concentrations were close to the detection limit. The introduction of the bivalve Tapes philippinarum Adams and Reeve in the lagoon and its harvesting by hydraulic and mechanical dredges strongly increased the amount of sediment resuspension and settlement. This phenomenon caused a marked increase in water turbidity and the disruption of the benthic microlayer of the lagoon bottoms composed by bacteria, microphytobenthos and small macrophytes. Significant correlations between microphytobenthos abundance and the suspended and settled sediment, and with the underwater light availability were found. In the areas affected by the highest sedimentation fluxes significant negative correlations were also found between the abundance of the microphytobenthos and phytoplankton communities. Many benthic taxa such as Amphora, Cocconeis, Navicula, Nitzschia, Pleurosigma and Thalassiosira, were found in all the water column samples and they were more abundant than exclusively planktonic diatoms. (C) 2002 Elsevier Science Ltd. All rights reserved
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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