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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
1

Effects of light, nutrients and Dreissena (Dreissena polymorpha and Dreissena bugensis) on benthic ecosystems in lakes

Qin, Peibing January 2007 (has links)
Thesis (PH.D.) -- Syracuse University, 2007. / "Publication number AAT 3281733"
2

SEASONAL CYCLES, DISTRIBUTION, AND BIOMASS OF CRUSTACEAN ZOOPLANKTON, AND FEEDING AND GROWTH OF YOUNG AMERICAN SHAD (ALOSA SAPIDISSIMA) IN THE HOLYOKE POOL, CONNECTICUT RIVER

ROSEN, RUDOLPH ALBERT 01 January 1981 (has links)
Interactions between young American shad (Alosa sapidissima) and their food (crustacean zooplankton and aquatic insect drift), and seasonal cycles and distribution of crustacean zooplankton were studied in the Holyoke Pool of the Connecticut River, Massachusetts from June 1977 through 1979. Aquatic insect drift was highest during darkness and in the mid-channel where flow was greatest. Erratic flow can increase drifting of some benthic invertebrates and enhance potential food available to fish. Automatic zooplankton samplers sampled four times each day throughout the study and were effective in capturing most species and size classes of crustacean zooplankton equally as well as a commonly used towed-net plankton sampler. Thirty-six species of Cladocera and 20 species of Copepoda were encountered; Bosmina longirostris and Chydorus sphaericus were the most abundant zooplankton. Total density and size and species composition of zooplankton entering the Holypoke Pool were similar to that which was discharged from the Pool, except during early July through September when losses of up to 1,000 kg dry weight of zooplankton occurred within the Pool. During summer, zooplankton was most abundant in the mid-channel where flow was greatest, and density decreased rapidly as zooplankton flowed downstream. The size distribution of zooplankton in the upper end of the Pool was similar in the near-shore and mid-channel, except during mid-July through September when the mid-channel contained higher frequencies of large organisms. The size distribution shifted toward the smallest size classes in a downstream manner during summer. The species and size composition of the zooplankton assemblage which entered the Holyoke Pool was typical of communities subjected to low levels of vertebrate predation, while that which was discharged from the Pool was typical of zooplankton communities subjected to intense predation by fish. Intrinsic factors of mortality, turbulence, sedimentation, filtration through vegetation, and predation by invertebrates and resident vertebrates seemed not to affect zooplankton abundance as strongly as predation by juvenile Alosa spp. Shad in the Holyoke Pool were progressively smaller downstream, except during the larval period. Mean lengths of shad at emigration were the smallest ever reported for the Pool and among the smallest reported elsewhere. Shad occasionally fed throughout the 24-hour period, although peak feeding generally occurred at dusk. Stomachs emptied within 8 to 10 hours. Shad selected an optimal diet based on food items available in the water column. Fish in upstream areas were able to feed in a more energetically profitable manner than those downstream. The abundance, size distribution, and spatial distribution of zooplankton was rapidly altered by feeding shad. Fish in upstream areas fed heavily on zooplankton of all sizes, but generally selected larger individuals; insects were also eaten. In the middle of the Pool, fish ate primarily insects but also utilized rare large zooplankton and the more abundant small zooplankton. Fish in the lower section of the Holyoke Pool utilized the remaining small zooplankton and some insects. The number of food items in stomachs progressively decreased downstream. Differential growth of shad within the Holyoke Pool was food based. The mean length of juveniles at emigration was inversely related to the number of adult shad lifted into the Pool. American shad may over-exploit their rearing grounds. It appears reproductively advantageous for Connecticut River shad to spawn as far upstream as possible. Wide variations in the size of American shad stocks may result partially from the relation between juvenile density and foods available in the nursery areas.
3

Invertebrate Phenology and Prey Selection of Three Sympatric Species of Salmonids; Implications for Individual Fish Growth

Ojala, Jeffrey V 01 January 2008 (has links) (PDF)
Growth plays an important roll in the survival of individual salmonid fish. Diet inevitably plays a significant role in the determination of salmonid growth, with these diets consisting primarily of aquatic macroinvertebrates, predominately insect taxa. Aquatic insects have a complex life history with most having a short, aerial adult period and an aquatic juvenile stage(s). The periodicity of this juvenile stage (voltinicity) can take a few months to a few years, with the vast majority lasting a single year. These numerous and overlapping phenologies therefore have a significant impact on the availability of prey that salmonid fish find profitable. Variation in the availability and use of macroinvertebrate prey may be an important determinant of growth variation in stream salmonids. However, few studies possess the requisite information to make these links explicitly, particularly for more than one co-occurring species. Drift and benthic invertebrate availability and selection were measured for three sympatric species of stream salmonids (Atlantic salmon, brook trout, and brown trout) in a long-term study site at West Brook, Whately MA through out 2003. Benthic macroinvertebrates were found to have a strong seasonal cycle of size and abundance in West Brook. Consistent with the numerical domination of univoltine aquatic insects in this stream, relatively few large, individuals are present in the spring prior to the peak of adult emergence, with many small, individuals in the fall. This phenology combined with abiotic factors (discharge, temperature) has significant effect on the availability of profitable salmonid prey. Examining the role of prey selection revealed that salmonid fish were able to capitalize on this seasonal abundance. Additionally, salmonid species were shown to change foraging tactics from drift feeding to the consumption of both benthic and terrestrial derived prey. These results suggest that spring is a period of high prey abundance producing a common pattern of high consumption and growth for all three species. Among-species differences in diet are most manifest during periods of resource scarcity. These results indicate that seasonal dynamics in physical conditions and invertebrate phenology may combine to produce a critical period for individual growth in stream salmonids.
4

The impact of freshwater invertebrate predators upon the structure of ecological communities

Jeffries, Mike J. January 1984 (has links)
No description available.
5

The influence of road runoff on the benthic macro-invertebrates of an unpolluted chalk stream

Cowley, C. January 1985 (has links)
No description available.
6

Trait and density mediated indirect effects in a three trophic level aquatic system with Asellus aquaticus and Aeshna

Jonsson, Sandra January 2009 (has links)
No description available.
7

Quantitative Understanding and Prediction of Lake Eutrophication

Bryhn, Andreas Christoffer January 2008 (has links)
Many lakes around the world have been exposed to increased nutrient input from anthropogenic sources such as sewage discharge and runoff from fertilised agricultural areas. This has led to eutrophication, manifested as intensified algal blooms, murky waters, oxygen depleted lake bottoms, and alterations of considerable parts of the foodweb. However, many of these lakes have also recovered, due to improved nutrient abatement techniques and to an improved quantitative scientific understanding of eutrophication and its causes. General, predictive models have played a crucial role in the latter development, as they have made it possible to quantitatively assess expected ecosystem changes from various planned actions against eutrophication. The present thesis has been aimed at improving the domain of validity and predictive power of a general, dynamic total phosphorus (TP) model (LakeMab) and to provide the basis for constructing a similar model for total nitrogen (TN). Among the findings in the thesis is that dissolved nitrogen gas is probably always available in excess for nitrogen fixation and nitrogen modelling in eutrophication contexts. Two papers have laid the ground for improved nutrient modelling in calcareous lakes, where sedimentation is particularly pronounced. Static models for predicting concentrations of particulate phosphorus, nitrogen, and organic carbon have been presented that may be incorporated into sedimentation algorithms in dynamic nutrient models. Boundary conditions for various flux algorithms have made it possible to greatly expand the domain of LakeMab for TP. The typical uncertainty of TP concentration values is 17% when predicted with LakeMab, whereas the uncertainty in predictions using older, static models is about twice as high. LakeMab may be very useful for resolving practical issues such as predicting climate-induced eutrophication and drawing up operational guidelines for achieving good water quality as prescribed by, e.g., the European Water Framework Directive.
8

Trait and density mediated indirect effects in a three trophic level aquatic system with Asellus aquaticus and Aeshna

Jonsson, Sandra January 2009 (has links)
No description available.
9

Effects of substrate relief, light intensity and herbivory on the distribution and abundance of periphyton in laboratory streams

DeNicola, Dean M. 26 April 1990 (has links)
Graduation date: 1991
10

MODIS algorithm assessment and principal component analysis of chlorophyll concentration in Lake Erie

Weghorst, Pamela Leigh. January 2008 (has links)
Thesis (M.S.)--Kent State University, 2008. / Title from PDF t.p. (viewed Sept. 28, 2009). Advisor: Donna Witter. Keywords: chlorophyll; Lake Erie; remote sensing; algorithm; atmospheric correction. Includes bibliographical references (p. 58-66).

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