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  • management  (3)
  • nitrogen
  • Springer  (4)
  • Copernicus
  • 1990-1994  (4)
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  • Springer  (4)
  • Copernicus
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 247 (1992), S. 121-132 
    ISSN: 1573-5117
    Keywords: coral reef ; degradation ; management ; macroalgae ; phase-shift
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Many coral reefs around the world have degraded to a degree that their present intrinsic value and utility are greatly reduced: (mass coral mortality followed by algal invasions; local depletions of reef fisheries; deficit of reef accretion compared to physical and biological erosion). Though we can sometimes identify proximal causes (outbreaks of coral predators and eroders; over-fishing; habitat destruction), we do not have a good understanding of how population, community and ecosystem structure and function differ in degraded from un-degraded reefs. The deficiencies in our understanding limit our ability to interpret the long-term significance of reef degradation, and therefore to develop scientifically based plans for conservation and management of reefs. A particular course of action, or lack of action, based on uncritical acceptance of any of the various views of temporal variability can lead to further deterioration of specific reefs. None of these views — that reefs are either inherently robust, inherently fragile, or inherently resilient — is true over all time-space scales. This presentation reviews various models and case studies which suggest that reefs can be knocked precipitously or move slowly from one phase (coral-dominated) to another (coral-depleted and/or algal dominated). Transitions in the other direction (‘recovery’) involve changes (e.g. succession) in populations and communities (of all reef-associated biota, not just sessile benthos), and in reef function (e.g. community metabolism, trophodynamics) which are of great intrinsic interest but only poorly understood.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-5036
    Keywords: bulk density ; epoxy resin impregnation ; image analysis ; macroporosity ; nitrogen ; stability ; strength ; structure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Soil aggregate stability, organic matter content, pH, bulk density, strength, and macropore attributes were assessed in order to evaluate the influence of grass root growth in a field sward. The amount of grass grown was varied by varying the quantity of applied nitrogen fertilizer: following one year with a uniform application rate, nitrogen fertilizer was applied over the subsequent three years to a compact soil at zero (N0), moderate (N1) and high (N2) rates. Differences in herbage production were evident in the three years of the contrasting nitrogen treatments. An index of soil aggregate stability increased in response to the increased grass growth promoted by heavier applications of nitrogen, but both bulk density and vane shear strength were unchanged. Binary images of the soil solid and pore space showed that for each treatment the largest volume of macropores occurred close to the surface, particularly in N0 where there was more pore space than in either N1 or N2. Analysis of the pore structure attributes of the binary images revealed further differences between treatments, in particular, at 40–80 mm depth, the soil in treatment N0 had fewer and smaller pores, and greater distance between pores, than the soil in the N1 and N2 treatments. The larger macropore volume in N1 and N2 constituted a major portion of the air-filled porosity when the soil was relatively wet. It was concluded that the root growth in the intensively cropped grassland was conducive to maintenance of a relatively stable and porous soil structure. An attendant increase in soil acidity close to the soil surface was a disadvantage of the larger nitrogen inputs.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Biogeochemistry 12 (1991), S. 135-148 
    ISSN: 1573-515X
    Keywords: fens ; management ; nitrogen ; phosphorus ; productivity ; vegetation ; wetlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract A fertilization experiment was carried out in 3 mesotrophic fens to investigate whether plant growth in these systems is controlled by the availability of N, P or K. The fens are located in an area with high N inputs from precipitation. They are annually mown in the summer to prevent succession to woodland. Above-ground plant biomass increased significantly upon N fertilization in the two “mid”-succession fens studied. In the “late”-succession fen that had been mown for at least 60 years, however, plant biomass increased significantly upon P fertilization. The mowing regime depletes the P pool in the soil, while it keeps N inputs and outputs in balance. A long-term shift occurs from limitation of plant production by N toward limitation by P. Hence, mowing is a suitable management tool to conserve the mesothrophic character of the fens.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5117
    Keywords: wetland characteristics ; threats ; conservation ; rehabilitation ; management ; ecological research ; The Netherlands
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Wetlands are among the worlds' most important, but also most threatened, environmental resources. Wetland losses have been in progress particularly from the industrial revolution onwards, because wetland functions could not successfully compete for space with other land uses. Wetlands became recently foci of conservation efforts because of the increased awareness of their importance in water management and wildlife conservation, and because of the diversity of their habitats. The Netherlands are relatively rich in wetlands: 16% of its' territory is regarded as internationally important wetland and 7% has been registered as such. The major Dutch wetland types are: coastal ecosystems, large riverine systems, base-rich freshwater systems, and nutrient-poor freshwater systems. Most threats to the Dutch wetlands are of man-made origin. They comprise: (1) Changes in hydrology leading to changed discharges, currents and desiccation; (2) Acidification; (3) Eutrophication; and (4) Toxification. Long-term threats are largely climate-change related, and concern temperature rise and the UV-B increase in irradiation. General conservation goals also apply to wetlands but Ramsar-registered wetlands have a special status. Conservation of the Dutch wetlands is difficult, because of the high population density of the country and its inherent threats. However, ecological targets and standards are increasingly set in national Policy Plans and international agreements. Rehabilitation and creation of wetlands is presently widely advocated, and sometimes realised. For ecological research, the sustainability of wetlands should get top priority. Such a research programme would focus on understanding the underlying ecological processes in natural and man-dominated wetland systems to prescribe conservation, rehabilitation and management strategies that would enhance the sustainability of these systems. Within this framework special attention should be directed to studies (1) At the ecosystem level of ecosystem parameters, of which natural oscillations and trends in time, and on which the impact of disturbances are quantified. Particularly these studies, in which often simulation models are used as tools for interpretation, can provide the basis for extrapolations in space and time; (2) On adaptation capacity and mechanisms of (groups of) species to extreme environmental conditions; (3) On (mutual) relationships between plants, animals and microorganisms (e.g. competition, grazing and mineralization); (4) On dispersion between small wetlands. For the contemporary quantitative assessment of the long-term effects of climate changes, the effects of temperature rise and increase in UV-B irradiation on individual species, communities and ecosystems should also be studied.
    Type of Medium: Electronic Resource
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