1,723,729 research outputs found
Effects of light and substrate on the benthic diatoms in an oligotrophic lake: a comparison between natural and artificial substrates
No full textBenthic diatoms form a particularly important community in oligotrophic lakes, but factors influencing their distribution are not well known. This study reports the depth distribution of living motile and total diatoms (living plus dead diatoms) on both natural (from sand to fine organic mud) and artificial substrates in an oligotrophic lake. On artificial substrates, motile diatom densities peaked in abundance (24–30 cells · mm?2) between 0.6 and 1.9 m depth; on natural sediment surfaces, motile diatoms were generally more numerous and peaked in abundance (925 cells · mm?2) at 1.3 m depth. Total diatom densities on artificial substrates were highest (1260 valves · mm?2) at 0.6 m depth, with very low values below 3 m depth; on natural sediment surfaces, total diatom abundances were generally much higher (21600 valves · mm?2) at 3 m depth and declined gradually with depth. Significant relationships were found between light and diatom densities on the artificial substrate. Ordination analysis indicated that substrate type significantly correlated with the variation of diatom composition on artificial and natural substrates. Our results suggest that in oligotrophic lakes, light influences benthic diatom abundance, whereas substrate type has more influence on benthic diatom composition
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
A portable hand-operated sampler for shallow-water surface sediments with special reference to epipelic communities
No full textA convenient, portable, hand-operated surface-sediment sampler for use in shallow water is described. Collection of replicable, undisturbed surface sediment samples from shallow-water locations is made simple. The sampler is highly portable for use at remote sites and can be operated by one person. It is especially useful for sampling in the 0.3–1.3 m water depth range where other samplers are often unsuccessful. This sampler consists of a PVC tube (about 33-cm length, 7.1-cm diameter) attached to a 1-m-long supporting rod. A lever system is used to close off the PVC core tube. In the open position, the core tube is inserted into the sediment to an optimal depth (typically 1-cm) so that a 1-cm disc of surface sediment is enclosed. This disc is then isolated by operating the lever and tube closure plate. The sampler and sediment sample (with an intact epipelon biofilm) are removed carefully so that most of the enclosed water drains away and the sample is retained intact. <br/
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