31 resultados para temporary streams

em Aquatic Commons


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The rainfall regime and the karstic nature of the subsoil determines the alternation of a period of flow and a period of drought for a large number of Mediterranean streams. Amongst this type of stream it is possible to distinguish temporary streams, characterised by a period of flow for several months permitting the establishment of the principal groups of aquatic insects; and ephemeral streams whose very brief period of flow permits the establishment of a community reduced to a few species of Diptera. This paper aims to study the structure of the communities which colonise this particular type of stream and the ecology of the principal species which constitute these communities. Four French temporary streams were examined and temperature regimes, dissolved oxygen, calcium and magnesium measured. Samples of fauna were taken regularly and the biotic composition established. The analysis of similarities between the three permanent streams are discussed and compared with permanent streams.

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When flow returns to a temporary stream a certain number of plant and animal species establish themselves more or less rapidly on the stream-bed constituting the initial phase of evolution of the re-population. This phase is essentially characterised by the ”awakening” of animal species that passed the dry season in a dormant state and by the development of the first unicellular algae that constitute the periphyton. Then they are succeeded by more or less stable animal groups and the structural complexity increases. The authors of the present study aim to analyse the dynamics of community succession from the return of water to the biotope until its drying up. It is attempted to determine the influence of the duration of flow on this evolution. This work is based on the analysis of population diversity with reference to its two complementary aspects, species richness and equitability. The River Destel which was studied for this project is situated in the Gorge of Ollioules near the town of Toulon.

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The purpose of this study was to measure and evaluate relationships between populations of benthic macroinvertebrates and fish, as well as variations in water quality in streams affected by acid Mine drainage. (PDF contains 21 pages)

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This article describes the streams of this unique area of Britain and reviews the published and some unpublished information that is currently available. None of the rivers in the New Forest are more than 30 km long. Many reaches have been artificially straightened, channelized and regraded since the 1840's. The stream waters are typically base-poor, with low nutrient concentrations. Primary productivity and standing crops of algae are predictably low when compared with other streams carrying higher concentrations of minerals and nutrients. The earliest records on the macroinvertebrate fauna go back to the late 19th Century. By 1940, over 20 species of Trichoptera and 10 species of Plecoptera had been recorded, but only four species of Ephemeroptera. Twenty species of fish occur in the streams of the New Forest of which the most common are brown trout, minnow, bullhead, stone loach, brook lamprey and eel.

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In Europe, temporary ponds are a naturally common and widespread habitat occurring, often in abundance, in all biogeographical regions from the boreal snow-melt pools of northern Scandinavia to the seasonally inundated coastal dune pools of southern Spain. Ecological studies in Europe and elsewhere also emphasise that temporary ponds are a biologically important habitat type, renowned both for their specialised assemblages and the considerable numbers of rare and endemic species they support. They are, however, a habitat currently under considerable threat. Most temporary ponds are inherently shallow and the majority are destroyed even by limited soil drainage for agriculture or urban development. The paper gives an overview of definitions of temporary ponds and examines their formation and abundance. The authors also summarise a visit to the Bialowieza Forest in Poland to investigate the occurrence of temporary ponds.

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The importance of ponds for biodiversity in Britain has been demonstrated by a number of studies. However, most of the research and interest has been directed at permanent waterbodies, and temporary ponds have been largely neglected. In this article the author present some preliminary findings from a project which aims to fill some of the many gaps in our knowledge of temporary ponds in Britain. The project, which runs for three years until the end of 2001, aims specifically to investigate the ecology of temporary ponds in England and Wales by describing (i) their wetland plant and macroinvertebrate communities, (ii) their physico-chemical characteristics, and (iii) their value as a biodiversity resource. The article focuses on the assessment of temporary ponds as a biodiversity resource and briefly considers aspects of species richness, rarity and distinctiveness. Where possible, temporary ponds are compared with other waterbody types, mainly permanent ponds from the National Pond Survey (NPS), to give the results a broader context.

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Flies are the largest order of wetland insects in Britain. Of 6668 known species, larvae of at least 1138 are considered to be aquatic while a large number, perhaps as many again, are associated with wetlands. Despite this abundance of species they have been neglected in nearly all studies of temporary ponds. The prerequisites that are usually quoted for surviving in temporary pools are an ability to reach maturity before the system dries out, physiological or behavioural mechanisms to survive the dry period, and an ability to recolonise. Larvae of many British wetland Diptera have these features, which should enable them to develop and survive in temporary ponds. Some examples are considered in this article, with brief comments on adaptations in insects from other geographical regions.

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To date, research on the ecology and conservation of wetland invertebrates has concentrated overwhelmingly on fully aquatic organisms. Many of these spend part of their life-cycle in adjacent terrestrial habitats, either as pupae (water beetles) or as adults (mayflies, dragonflies, stoneflies, caddisflies and Diptera or true-flies). However, wetland specialist species also occur among several families of terrestrial insects (Williams & Feltmate 1992) that complete their whole life-cycle in the riparian zone or on emergent vegetation. There are 441 terrestrial invertebrate species which characteristically occur in riparian habitats along British rivers. Most of these species belong to two families of predatory beetles: the ground beetles (Carabidae) and the rove beetles (Staphylinidae). This paper describes the diversity of ground and rove beetles around ponds, summarises life-histories, hibernation strategies, and morphological and behavioural adaptions.

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Although there is a growing awareness of the value of temporary ponds in Europe, there is still remarkably little information available to help guide their conservation and management. General principles which can be used to guide the management of temporary ponds as a whole have yet to be established. The aim of this article, therefore, is to give a broader overview of the main principles of temporary pond conservation, particularly by building on a number of general principles for managing ponds previously described by Biggs et al. (1994) and Williams et al. The authors emphasise the importance of surveys in order to get data on which to base management strategies. The main principles of temporary pond management are described, and examples of three case studies of ponds in England are given.

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More than 4000 ponds have been created or restored in Denmark since 1985 as part of a large-scale pond-digging programme to protect endangered amphibians in particular and pond flora and fauna in general. Most ponds are created on private land with public financing. The programme was triggered by, among other factors, a drastic decline in amphibian populations in Denmark between 1940 and 1980. However, in recent years there has been an increased awareness in Denmark that temporary ponds are important for the conservation of some of the most rare amphibian species, such as fire-bellied toad Bombina bombina, natterjack toad Bufo calamita and green toad Bufo viridis. Other rare species such as moor frog Rana arvalis and European tree frog Hyla arborea also benefit from temporary ponds. The last 15 years of work on the conservation of endangered species and their habitats has resulted in a last-minute rescue and a subsequent growth in the size of most Danish populations of fire-bellied toad and green toad; some populations of the relatively more common natterjack toad have also increased. The creation of temporary ponds plays an important role in the success of these three species. The creation of ponds to help restore viable populations of the most rare amphibians has not been easy. To study the conditions that may need to be created, Danish herpetologists searched for areas with temporary ponds that had good water quality, natural hydrological conditions and a management regime influenced by traditional agricultural methods. The paper gives an overview of pond creation and restoration projects in Denmark and Poland and their significance for amphibian diversity.

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Seasonal changes and flooding have an extraordinarily great influence on the drift of organisms. The free water space plays the main part in the provision of food for some fish (Salmo trutta - trout): drift and content of the stomach are balanced here (Simuliidae): whereas others (Thymallus vulgaris) only selectively chose certain animals living at the bottom (molluscs). The total drift, drift of organisms and drift of organic material and minerals, plays a main role in the rate of production in streams. Besides the biology of the organisms living on the river bed, also the geological and hydrographical situation of the area plays a very important role for the composition of the drift. During the years 1964-1966 three streams in the characteristical geological formations flysch, gneiss and chalk of lower Austria were studied in regard to their drift. The Tulln (above St. Christopen), the Krems (above Senftenberg) and the Schwarza (above Hirschwang) seemed to be ideal for this comparative study because they are easy to reach. After summarising the hydrography and chemistry of examined rivers, the author examines the relationship between water level and total drift and the stratification of the total drift before analysing the drift of living organisms. Also considered are seasonal changes of drift of organisms and drift of exuviae.

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Few detailed studies have been made on the ecology of the chalk streams. A complex community of plants and animals is present and much more information is required to achieve an understanding of the requirements and interactions of all the species. It is important that the rivers affected by this scheme should be studied and kept under continued observation so that any effects produced by the scheme can be detected. The report gives a brief synopsis of work carried out during the second year of a four year ecological study sponsored jointly by the Thames Water Authority and the Central Water Planning Unit. It assumes some familiarity with the investigations carried out on the River Lambourn during the preceding three years which was sponsored jointly by the Thames Conservancy and Water Resources Board (immediate predecessors of the present sponsoring organisations). (PDF contains 31 pages)

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Few detailed studies have been made on the ecology of the chalk streams. A complex community of plants and animals is present and much more information is required to achieve an understanding of the requirements and interactions of all the species. It is important that the rivers affected by this scheme should be studied and kept under continued observation so that any effects produced by the scheme can be detected. The report gives a synopsis of work carried out between 1971 and 1979 focusing on the present phase 1978-1979. It assumes some familiarity with the investigations carried out on the River Lambourn during the preceding years. The aims of the present phase of the project may be divided into two broad aspects. The first involves collecting further information in the field and includes three objectives: a continuation of studies on the Lambourn sites at Bagnor; comparative studies on other chalk streams; and a comparative study on a limestone stream. The second involves detailed analyses of data previously collected to document the recovery of the Lambourn from operational pumping and to attempt to develop simple conceptual and predictive models applicable over a wide range of physical and geographical variables. (PDF contains 43 pages)