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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 30 (1983), S. 0 
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Although mean size provides a useful value for characterizing sediments, it is an inadequate expression of the interaction between sediments and hydraulic regimes and many authors have explored the significance of other statistical moment measures in different parts of the particle size spectrum. Few publications, however, have described such relationships over a very wide range of particle sizes. Using a combined data base (of marine and lacustrine sediments) we have been able to demonstrate the following:The distributions of standard deviation (and entropy) values are repeated in similar form on either side of the sand size class, describing mixtures between sands and gravel and sands and clay.Skewness is modified by the hydraulic response of the sediment and a skewness divide is present at about 2.7 φ, where it coincides with the minimum shear velocity required to initiate particle motion. This divide may be used to distinguish between high and low energy regimes.Kurtosis, like standard deviation, is a measure of the mixing of end member populations but it is more sensitive to changes in the tails of distribution curves. The maximum positive peak of kurtosis, at about 2.5 φ, lies close to the skewness divide (in our data).By using skewness/kurtosis plots it is possible to define separate field distribution for sediments which, to a greater or lesser degree, appear to conform to hydraulic equilibrium.By using sediments which are close to equilibrium (and lie at or close to our skewness/kurtosis boundary curves, it should be possible to define hydraulic shear velocities, at the time of formation. Values may be established by empirical relationships or by defining the break-point (traction and intermittent suspension) between linear components of individual sample φ size/probability distribution plots. Such relationships should be enhanced by using hydraulic equivalent diameters instead of sieve diameters.In fine sediments, the use of fractional (silt: clay) ratios offers sensitivity at a level comparable to that of skewness/kurtosis plots and may be more easily computed.
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 204 (1964), S. 174-175 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Hecent work (unpublished) in the Harlech Dome has shown the structural pattern to be more complex than has previously been supposed; consequently certain of the methods used by Kopstein are now known to be inapplicable. He concluded that, with the exception of the Dolwen Grits, palseocurrent ...
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 163 (1988), S. 1-19 
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This paper presents a background description of the basin and an overview of the physical, chemical and biological limnology of Georgian Bay and the North Channel. Further, it describes the expansion of European settlement and the association of cultural impacts with urbanization, industry and transportation. The history of the fishery is briefly outlined, and changes in the structure of fish communities are related to fishing pressures and the introduction of exotics. In the concluding sections of the paper, we discuss present and future concerns which may be related to water quality and water quantity issues and, also, to the stability of re-establishing fish communities.
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  • 4
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The study site covers a spur of the submerged Niagara escarpment and part of the Flowerpot basin of Georgian Bay. Bedrock outcrops occur on islands and shoals but much of the area is covered by glacial till (10–20 m thick). Glaciolacustrine clay occurs in thin patches on the spur; in the deepest parts of the area, however, it is nearly 70 m thick. The distributions of Recent sediments which comprise lag-gravels, sands and silty clays, reflect major postglacial lake level changes in the Huron — Georgian Bay basin. Sediment geochemistry in Georgian Bay is similar to many other parts of the Great Lakes but calcium charbonate levels are lower than expected, except in some deposits of gaciolacustrine clay. There is little evidence of anthropogenic impact in the content of trace metals, although Pb likely includes a portion derived from atmospheric loading; Hg is usually present at very low levels but there are anomalously high values in some deepwater modern muds. In the bottom sediment habitat of modern benthos, the distribution of chironomids seems to reflect silt content. Oligochaetes are least in areas of thin Recent mud or exposed glaciolacustrine clay. Pontoporeia and sculpins are most numerous at depths between 50–110 m. Bottom tracks and other bed marks cover extensive areas of the deepwater lake sediments.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 257 (1993), S. 153-164 
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Laguna Lake is a large lake in the central Philippines, close to Metro Manila. Agricultural, industrial and urban development is expanding rapidly in the Laguna Lake basin, giving rise to many forms of environmental stress in the lake and surrounding watershed. In particular, the lake appears to be subject to high rates of sedimentation, and the yields of both open lake and captive fisheries have severely declined. Exploratory coring was undertaken to provide a better understanding of lake sedimentation and long term trends in lake productivity. Actual rates of sedimentation are thought to be about 1–1.5 cm y−1 and are likely about half the calculated rate (unadjusted for sediment mixing). Trends in diatom content and surrogate data (including loss on ignition) suggest major variations which may correlate with changes in productivity and food-web structures.
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 176-177 (1989), S. 99-110 
    ISSN: 1573-5117
    Keywords: sediment texture ; fine sediments ; silt/clay ratio ; dispersion ; Great Lakes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The dispersion of fine sediment is greatly influenced by factors that induce flocculation, and which thereby determine whether particulates will settle in aggregate form or as discrete grains. The transport and deposition of silt and clay particulates in both marine and non-marine environments may be influenced by flocculation. Because the transport of sediment-associated contaminants is largely influenced by the behaviour of sub sand-size material, it is important to understand the factors which influence patterns of deposition. The silt/clay ratio has been used in an attempt to simplify description of the physical processes of sediment/water interaction, and most examples have been drawn from the Great Lakes. The silt/clay ratio has been related to other characteristics of the total particle-size distribution. As an indicator of many sedimentary conditions, it must be coupled with other measurements of particle-size.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 176-177 (1989), S. 111-124 
    ISSN: 1573-5117
    Keywords: sediment texture ; sand size ; percent mud ; dispersion ; Liverpool Bay ; River Mersey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In part 2 of this contribution, examples are drawn from the River Mersey and Liverpool Bay illustrating the use of simple statistical parameters to describe dispersion of sands and muddy sediments. The River Mersey and Liverpool Bay, eastern Irish Sea, were sites of intensive studies on the dispersal of dumped harbour mud and sewage sludge during the mid 1960's–70's. The combined effects of strong tidal scour, wave action and shoreward near-bed residual drift result in shoreward transport of large volumes of sand in the bay. Large amounts of mud (silt/clay mixtures) oscillate in the river estuary, and naturally derived and dumped muds also move shoreward in the bay. Unpublished historic geochemical data have been combined with reprocessed particle size data and both have been used to reassess sedimentological techniques for defining transport and dispersal pathways. River and bay muds have similar size compositions, but river muds have excess Cd 〉 V 〉 U 〉 As = Zn relative to bay muds. The lower relative concentrations of heavy metals in the bay are thought to reflect desorption and degradation of organic matter from the river. Trends in sediment distribution data based on the means of the sand size fraction, alone, provide sensitivities comparable to those of higher order moment measures and are usually easier to interpret than full size spectrum analyses.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 213 (1991), S. 1-75 
    ISSN: 1573-5117
    Keywords: Lake Ontario ; cultural development ; environmental impacts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Lake Ontario is the lowest in the chain of five Great Lakes which form part of the boundary between Canada and the United States. Although European exploration began as early as 1615, it was not until the mid-18th Century that permanent settlement began in the Great Lakes basin. Construction of the Erie Canal which links Buffalo with New York via the Hudson River, and its branch to Oswego, strengthened ties between settlements around the lower Great Lakes (lakes Erie and Ontario) and rapidly growing populations along the Atlantic seaboard. The coming of railroads greatly expanded these ties, and provided a direct link between Canadian settlements and the port of Montreal. Over the past 200 years, successive waves of immigrants entered the region, particularly from Europe. Cultural development has resulted in a wide range of environmental impacts throughout the Great Lakes basin. Impacts have been particularly severe in Lake Ontario. Major changes in water quality and the structure of biological communities have resulted from forest clearance, agricultural expansion, intensive fishing, industrial and urban development, and lake level control. Introductions of exotic species, inputs of nutrient and toxic contaminants, and the effects of climatic variation and modification of microclimates have all interacted such that it is often impossible to establish singular cause and effect. The effects of cultural impact became most severe during the early 1970s and prompted strong support for the International Great Lakes Water Quality Agreement (1972) between Canada and the United States. In response to this agreement and subsequent revisions, contaminant loadings have been greatly reduced. Present water quality is generally good in Lake Ontario although some persistent toxic substances remain a problem. Programs to restock the lake have also provided major benefits. Although much further work remains, Lake Ontario is undoubtedly a good example of successful large scale remedial actions.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 235-236 (1992), S. 321-352 
    ISSN: 1573-5117
    Keywords: Pontoporeia hoyi ; sediment-water interface ; organic carbon
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The physical and chemical characteristics of the sediment-water interface greatly influence distributions of the bottom-feeding amphipod Pontoporeia hoyi which is a major component of the Great Lakes aquatic food-webs. Sediment-water interface samples from the Great Lakes indicate that Pontoporeia densities are positively correlated with sediment concentrations of organic carbon, particularly in the upper depth range of the species. Pontoporeia is not found in anoxic sediments. Growth rates and production of Pontoporeia are influenced by the quality of food supplies and there appears to be a seasonal response to the down-flux of plankton detritus. Comparisons of numerations and distribution patterns also revealed an apparent positive relationship between Pontoporeia and sediment-associated bacteria. Interlake comparisons of population densities provide no clear evidence of any large scale impact by contaminated sediment on this species. Depending upon the extent to which organic carbon (OC) is assimilated in the water column, bottom sediments may store and buffer the quantity of OC available to Pontoporeia. Thus, if the annual down-flux of OC remains generally constant, populations of Pontoporeia should also remain constant unless influenced by changes in predation intensity. Numerations of Pontoporeia revealed that populations of this amphipod are much larger in Lake Michigan than in Lake Ontario. We suggest that much of this difference can be accounted for by different forms of predator-prey interaction near the base of the benthic food-web. Commercial fisheries data tend to support this idea. We also speculate that differences in the concentration of dissolved silica may figure prominantly among factors that affect Pontoporeia population densities.
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    Journal of aquatic ecosystem stress and recovery 5 (1996), S. 153-175 
    ISSN: 1573-5141
    Keywords: lake trout ; spawning habitat ; Great Lakes basin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract We provide further insight into the reproductive ecology and spawning requirements of lake trout. New comparative information about substrate characteristics, sediment transport, quality of interstitial water at spawning substrates, and the role of temperature in site selection and time of spawning is given for lakes Simcoe and Manitou (Ontario) and Seneca Lake (New York). Spawning lake trout commonly use stable lag deposits derived from glacial sediments, or relict features such as fans, bars or submerged talus slopes. Artificial breakwaters of broken material may also provide suitable substrates. Optimal particle sizes range from 4 to 10 cm diameter but larger materials to 30 cm are also successfully utilized for spawning. The transport of finer particulates by wind generated water movements may limit the suitability of some substrates and successful spawning sites are usually remote from depositional effects. Successful embryo development is associated with low nutrient conditions, with high dissolved oxygen (〉7 mg L-1) and with low un-ionized ammonia (〈12.5 μg L-1) in the interstitial water of spawning substrates. Shallow-water spawning appears to be the common strategy of colonizing lake trout. Some deepwater spawning in the Great Lakes may reflect initial colonization in shallow-water and adaptation to later increases in water level, but some may also reflect unique behavioural and physiological adaptations. Temperature is an important cue, and many wild and hatchery stocks spawn at 8 to 13 °C with latitudinal shifts in the actual time of spawning. These requirements are summarized as a dichotomous key for evaluation of approaches to restoration of lost or damaged lake trout stocks.
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