1,721,142 research outputs found
The Diatoms in the Area of the Town Treuchtlingen
No full textThis book represents the „Lebenswerk“ (‘work of a lifetime’, as he himself calls it) of Erwin Reichardt, world-renowned amateur diatomist and one of the leading Gomphonema Ehrenberg specialists. The title could be translated as ‘The diatoms in the area of the city of Treuchtlingen’. It demonstrates the unimaginable wealth of diatoms that can be found, if an area of only c. 100 km2 is documented in depth. According to him (and I heartily agree), it is likely to be "the most extensive and detailed representation of the diatoms of a region that has ever been published". It comprises two large (30x24 cm) books including 1184 pages and, most importantly, over 10,000 photographs arranged in more than 450 plates (the second volume comprises only plates)
DIATOM COMMUNITIES OF SPRINGS IN THE SOUTHERN ALPS
No full textIn the Adamello-Brenta Regional Park (Trentino, Italy), the diatom communities of 30 mountain springs, 15 on crystalline and 15 on carbonate substratum, were studied between 1993 and 1996. Two of them, one from each substratum type, were sampled monthly for a more detailed investigation of seasonal changes in community structure. The diatom flora of these springs consisted of 250 diatom taxa and showed similarities with springs and headwater stream diatom communities from different geographic areas. Characteristic spring taxa (crenophiles) were present, but included mainly subdominant and rare taxa. Diatom taxa numbers were similar to those found for mountain streams with the lowest values found for stones in carbonate springs; nevertheless the community structure of epilithic and epiphytic samples was found to be similar and more or less constant over the seasons. By numerical methods, diatom communities were clearly related to a pH gradient. A group of species, located at the lower end of this gradient, is typical of anthropogenetically acidified running waters. © 1998 Taylor & Francis Group LLC
Effects of water-level fluctuations on lakes: An annotated bibliography
No full textWater-level fluctuations (WLF) in lakes and rivers, especially their extent, frequency and duration, are dominant forces controlling the functioning of these ecosystems. In particular, WLF play an important role in the lake's littoral and aquatic-terrestrial interface processes. WLF may take place on different spatial and temporal scales under natural conditions but water levels have been artificially modified in regulated lakes, and their impacts are expected to be enhanced within the actual global change scenarios with forthcoming management problems. This article presents an overview on the literature published on this important topic since 1991 by using journals indexed in the ISI Web of Knowledge. The overall objective was to examine temporal and spatial trends in publications on WLF, the specific aspect of WLF concerned and their main effects. Throughout the article we have used case studies to illustrate different effects of WLF on the variety of lake habitats and indicators that have been studied. Overall, the number of papers published on the subject since the 1990s has risen steadily, when less than ten papers were published each year; until 2006 and peaking in 2005. The greatest number of papers on WLF has been carried out in Europe and North America (c. 73%). These data also showed that the effects of WLF have not been studied equally for different groups of organisms. There is a greater interest on macrophytes, which are the most studied group of organisms (18.4% of the papers). Nearly 7% of the papers deal with algae, and zooplankton and invertebrates account for a 7% followed by fish. WLF effects on ecosystems are very complex, and the biological effects in lakes are greatest in shallow water and littoral areas, where even small changes in water levels can result in the conversion of large areas of a standing-water environment in air exposed habitats. Finally, these data might serve to highlight knowledge gaps still existing on this topic and, in particular, some of the approaches that can potentially contribute to solve several of these lacunae are explored. © 2008 Springer Science+Business Media B.V
Understanding the natural variability of diatom assemblages in springs of the Adamello-Brenta Nature Park (south-eastern Alps) on a temporal scale
No full textIt is thought that long-term monitoring is an essential tool through which conservationists and managers (i) are alerted when the system departs from the natural state, (ii) can check their environmental policy, and (iii) can detect disturbance effects. However, while long-term studies are growing in number, the lack of information on the background rates of natural changes could lead to a biased interpretation of results. In this study we analyzed the diatom composition of yearly samples (14 -16 yrs) in four springs with the following goals: (1) to estimate the consequences of sampling-related processes on the species composition and relative abundance; (2) to determine the form of the assemblages' variation, evaluating whether the assemblages can be predicted by cyclic, directional, or stochastic changes; (3) to test if, and to what extent, the diatom variability (variation in species composition, relative abundance and diversity) on a temporal scale is driven by the environment; (4) to evaluate the degree of temporal concordance among the diatom assemblages inhabiting four springs. Results showed that because the effect of sampling was inversely proportional to the species abundances, the presence of the least abundant species over the years were mainly a result of chance. The analyses allowed us to discriminate between stochastic and directional patterns, revealing the ongoing changes in two out of four springs. Because the environmental variables did not explain a significant portion of this variability, other hypotheses are put forward. The assemblages' dynamics of species composition over time were significantly synchronous in two out of six couples of springs, and regardless of the environment. This result can suggest that internal, within springs, drivers may be more important than extrinsic forces operating over regional spatial scales. Overall, these results provide a benchmark of diatom variability over time and in natural conditions delimiting the "limits of acceptable changes". © 2011 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany
New findings on the ecology and ultrastructure of Cymbella ancyli cleve
No full textCymbella ancyli is a diatom species inhabiting oligotrophic lakes with a carbonate substratum. C. ancyli has a relatively wide geographic distribution and is considered to be rare in present day assemblages, while it is more common in subfossil material (particularly in the Ancylus Clay). During a comprehensive investigation on the ecology and depth distribution of benthic diatoms of Lake Tovel, C. ancyli was found to colonise stone and rock surfaces in the intermediate depth zone of the lake. The intermediate depth zone is stable, because it is not influenced by water level fluctuations, temperatures are low and nearly constant, and light is attenuated but sufficient. This niche may constitute a relict refugium for Cymbella ancyli. Analysis of the ultrastructure of C. ancyli revealed that apical pores were present, not only at the footpole, but also the headpole. This finding gives further support to the opinion that this taxon is closer taxonomically to Cymbella sensu lato than to Gomphocymbella. © 2003 Taylor & Francis Group, LLC
Using spring biota of pristine mountain areas for long-term monitoring
No full textThirty springs in the Adamello-Brenta Regional Park (Trentino, Italy) distributed over a large altitudinal range (from 1073 to 2172 m a.s.l.) were studied between 1992 and 1996. A high diversity of plant and animal communities including algae (mainly cyanophytes and diatoms), mosses and higher plants, macroinvertebrates (the main groups being midges, stoneflies, caddisflies), water mites, microcrustaceans, and crenobiontic snails was identified. The springs situated in pristine areas allow the detection of slight shifts as well as long-term effects of impacts on their drainage basins much more clearly than freshwater environments altered by human activity. In this paper we discuss the use of spring biota for the definition of the trophic status, ongoing acidification processes, and organic pollution. After a broad screening of the biota within a basic investigation, continuous survey of water mites is recommended for checking the persistence of stable conditions and the survey of diatoms for monitoring acidification and eutrophication processes
The role of environmental variables in structuring epiphytic and epilithic diatom assemblages in springs and streams of the Dolomiti Bellunesi National Park (south-eastern Alps)
No full textDiatom assemblages were investigated in 16 springs and five streams of the Dolomiti Bellunesi National Park (south-eastern Alps, Italy), by collecting individual samples of the main substrata (stones, bryophytes, surface sediment), and measuring an extensive number of morphological, physical, and chemical variables. An empirical grouping of these aquatic ecosystems, based mainly on morphological features and physical parameters, mostly agreed with groupings produced by non-metric multidimensional scaling. Significant differences among the diatom assemblages were found among the groups identified; however, these differences were more significant in the epilithic than in the epiphytic assemblages. Epiphytic and epilithic diatoms differed significantly according to: a) the identity of several species, b) the relative abundance of some other species, c) the Bray-Curtis distance between the assemblages, and d) taxa richness and diversity index. However, on studying species composition by canonical analysis, with reference to environmental variables (here called macrohabitat) on the one hand, and the type of substrata (stones and mosses) on the other, it was shown that the macrohabitat was responsible for more than 40 % of the variability among diatom assemblages, whereas the microhabitat (i.e. different substrata) accounted for only 3 %. Multivariate analyses (CCA) showed that the environmental factors most influential in structuring diatom assemblages were substrate particle size (influenced in turn by current velocity), permanence of flow, shade, nitrates, and total phosphorus. Characteristic groups of species were identified in the different morphological and hydrological types of springs and streams. Stream sites were often affected to a certain extent by organic pollution, even within the protected area, and consequently colonized by cosmopolitan, eutraphentic or tolerant taxa. In springs, in addition to common and widely distributed species, many poorly known, rare, or Red List species were found, in particular among the less abundant taxa. Our study therefore highlights the important role of springs as valuable habitats for the conservation of aquatic biodiversity. © 2009 E. Schweizerbart'sche Verlagsbuchhandlung, D-70176 Stuttgart
Phylogenetic position of Geitleribactron purpureum (Synechococcales, cyanobacteria / cyanophyceae) and its implications for the taxonomy of Chamaesiphonaceae and Leptolyngbyaceae
No full textOver the last decades, the taxonomy of cyanobacteria has been considerably improved and restructured due to the increase in data output from molecular phylogeny. Recently, a new protocol was developed that enables reliable sequencing of 16S rRNA genes in cultivation–resistant cyanobacteria using analysis of single cells, filaments, or colonies. In the current study, we examined a sample of a heteropolar unicellular cyanobacterium, Geitleribactron purpureum, from the holotype material (deep epilithon of Lake Tovel, Western Dolomites, Italy). We isolated and purified single colonies of G. purpureum, and subjected them to direct PCR and 16S rRNA gene sequencing. We obtained a congruent set of sequences that formed a unique, isolated cyanobacterial lineage, showing phylogenetic clustering among simple filamentous genera of the family Leptolyngbyaceae. We provide evidence for deep polyphyly in Chamaesiphonaceae, and suggest that Geitleribactron should be re–classified in the Leptolyngbyaceae
Lake benthic algae: Toward an understanding of their ecology
No full textLake phytoplankton studies outnumber studies on lake periphyton by an order of magnitude, and most periphyton research has been done in streams. Most benthic algal taxa found in lakes also can be found in lotic systems, but assemblages and taxa differ in a number of ways. The ecological characteristics of some lake benthic algae reflect habitat coupling. Littoral zones (benthic areas above the light compensation depth) are areas of high productivity and biodiversity. The proportion of benthic and planktonic primary production (autotrophic structure) is a key ecosystem property. The distribution of lake benthic algae is markedly influenced by the depth gradient and substratum, and assemblages change with depth from epilithic and epiphytic rheobionts to epipsammic and epipelic limnobionts. At shallow depths, periphyton must cope with the effects of high radiation, water-level fluctuations, wave action (e.g., desiccation, ultraviolet radiation exposure, shear stress), and seasonal shifts in temperature. This situation selects for widely distributed rheophilic species. In contrast, the deeper littoral zone is stable and hosts a distinct subset of lentic periphyton. However, species experience low light intensity, which becomes increasingly severe with increasing depth, and are often threatened by eutrophication-driven increased shading by phytoplankton. Besides change across depths and substrata, adaptations to disturbance levels, competition, microdistribution of phenological stages, and physiomorphological regulation generate multiple and complex spatial patterns at different scales. Lake shores are the focus of human activities with significant consequences for periphyton. In this review, we introduce a series of 15 papers on the topic and suggest directions for future research. Overall, this special series illustrates that, despite the many important ecosystem services provided by lake benthic algae, the topic is understudied. © 2014 by The Society for Freshwater Science
Geissleria gereckei sp. nov. (Bacillariophyta) from leaf-litter covered stones of very shaded carbonate mountain springs with extremely low discharge
No full textA new benthic freshwater diatom, Geissleria gereckei sp. nov., was identified from light and scanning electron micrographs. The most characteristic morphological features are the valve outline (elliptical, but with lateral margins that can range from slightly convex to slightly concave and also straight, and protracted, almost capitate ends), the size and length/width ratio, and the pattern of the striae around the central area. The new species was found to be epilithic, and characteristic of leaf-litter covered stones of very shaded carbonate mountain springs of the Italian Alps with extremely-low discharge (likely to be affected by seasonal desiccation). Very-low-discharge springs host a highly specialized diatom microflora, and are likely to increase in number in the near future due to the reduction of water, which is predicted to be caused by climate change in many regions. © 2009 Japanese Society of Phycology
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