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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Polar research 10 (1991), S. 0 
    ISSN: 1751-8369
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geography , Geosciences
    Notes: Time series data of phytoplanktonic and bacterial biomass during the ice retreat period at different latitudes in the Weddell Sea and Prydz Bay areas show a distinct delay in the development of bacteria with respect to phy'oplankton. Use of a general ecophysiological model of bacterial growth, along with direct in situ measurements of growth and mortality rates, allowed the simulation of the observed timing of bacterial development. It is suggested that the uncoupling between phytoplanktonic and bacterial development at the earliest stage of the spring ice-edge related algal bloom is not the result of the low temperatures occurring in the Southern Ocean but rather is due to the macromolecular nature of the dissolved organic matter released from phytoplankton.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1573-515X
    Keywords: Nitrogen cycling ; non stationary diagenesis ; recently impounded basin ; denitrification ammonification
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract The Méry-sur-Oise (France) storage reservoir is an artificial basin of 9 m average depth, fed by water from the river Oise with a mean residence time of about 4 days. Sediments are accumulating at a rate of about 0.7 cm/month. In the sediments, two fractions of organic nitrogen with different rates of bacterial degradation could be distinguished, one associated with fresh phytoplankton, the other made of detrital and more refractory compounds. The fluxes of oxygen, nitrate and ammonium across the sediment-water interface were measured with a bell-jar system at different seasons during a 3 year period following flooding of the basin. The measurements show clear seasonal variations in relation with the variations of temperature and input of fresh phytoplanktonic material to the sediment. In addition, a long term trend of increasing ammonium was observed. Measurements were also carried out after dredging of all accumulated sediments of the basin. They showed a considerable reduction of the flux of nitrate to the sediments and a significant reduction of the flux of ammonium to the water column. These results are interpreted in the light of a non stationary model of N diagenesis in accumulating sediments. This model is able to predict at least the general trends of benthic N cycling of basins during the early stage of their ecological succession.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-5117
    Keywords: Bacterioplankton ; bacterial growth rate ; bacterial mortality ; bacterial grazing ; oligotrophy ; eutrophy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Measurements of bacterial biomass, production and mortality have been carried out in a large range of aquatic environments, including eutrophic and oligotrophic ones. The general trends of variations of bacterial biomass, size, specific growth rate and mortality rate in all these environments are examined. The overall flux of bacterial production is taken as an index of the flux of organic matter available to bacteria, thus characterizing the richness of the environment. Bacterial biomass is roughly proportional to richness, while mean cell size increases with it. The turnover rate of biomass, as revealed either by growth or by mortality rates, appears to be fairly independent of richness. These observations are compatible with a simple resource-limited (bottom-up controlled) model of the dynamics of bacterioplankton. On the other hand, they are in contradiction with the predictions of a predator-controlled (top-down controlled) model.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1573-5117
    Keywords: Sand-pit lake ; ecological modelling ; nutrient loading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A large data set (n = 154) of phytoplankton production and biomass in relation to physico-chemical environmental factors was collected from 1979 to 1986 in a recently created sand-pit lake (Paris suburbs). These data are well suited to interpret the oligotrophication observed along the 8 years period, characterized by a regular decrease in chlorophyll (from 16 to 4 µg l-1 as annual averages). A model describing the ecological functioning of the lake has been established. Biological processes related to phyto-, bacterio- and zooplankton as well as sediment-water interactions, are described within several submodels. Most of the parameters involved were determined by in situ measurements in this or similar environments The model provides a good simulation of observed data and confirms that the reduction of nutrient loading, resulting from the diversion — in 1981 — of a sewer previously discharging into the lake, was responsible for the oligotrophication of the system. The model allows to explore the response of planktonic compartments accross a gradient of nutrient loading. The role of hydrology is also tested. The systematic run of the model with and without zooplankton leads to a better understanding of top-down control.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-5117
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Phytoplankton development in river systems is under the control of various meteorological, hydrological, chemical and biological factors. Because of the continuity of the aquatic systems which progress from headwaters to the largest rivers, the interplay of these control factors can only be understood at the scale of the entire drainage network. The RIVERSTRAHLER Model, based on the concept of stream-order, has been established for that purpose. It has been applied here on two rivers from the Seine basin: rivers Marne and Oise. It is shown that hydrological factors determine the time of onset, and the position within the drainage network, of the spring algal bloom. Phosphorus availability, when limiting, controls the intensity of the bloom. During summer, top-down control, linked to grazing and other causes of mortality, has a marked impact on algal dynamics.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1573-5117
    Keywords: Seine river ; ecological modelling ; validation ; anthropic impacts
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The Seine river crosses the most densely populated and industrialized area of France, Paris (16 million inhabitants), surrounded by fertile land with intensive agriculture. In the framework of a CNRS (Scientific Research National Center) research project, computer programs have been designed to tackle problems related to eutrophication, non-point pollution and the impact of sewage during dry or wet periods (urban runof and sewage network overflow). The PROSE software has been specially designed to simulate the behaviour of the most disturbed stretches of the Seine ecosystem on the last 300 kilometers of the river, upstream of the estuarine area. The 1-D hydraulic sub-model of PROSE is based on a finite difference solution of Saint-Venant equations solved with the Preissman scheme. It simulates steady state situations as well as highly transient situations such as fast changes in river discharge during rainy periods or dam motions. The biological sub-model is based on the RIVE model, describing the major processes in a river ecosystem: primary production, heterotrophic bacterial activity and organic matter decomposition, major nutrients species (nitrogen, phosphorus), nitrifying activity and oxygen balance. Water column and sediment variables are simulated. Most of the parameters have been estimated during laboratory experiments or field studies. Different situations observed between 1989 and 1991 allowed a detailed validation of the model. The model was then used to explore the reaction of the ecosystem (particularly its oxygen status) to changes in physical constrains (discharge, reoxygenation at dams) or in biological processes (release of microorganisms accompanying waste water discharge).
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Hydrobiologia 111 (1984), S. 57-63 
    ISSN: 1573-5117
    Keywords: river ; oxygenation ; primary production ; respiration ; eutrophication
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Gross primary production, community respiration and reaeration coefficient were determined during an annual cycle on the Viroin River (South Belgium), based on the daily variations of dissolved oxygen concentration. Reaeration coefficient remains remarkably constant (0.26 h−1) during the year in spite of discharge variations. The autotrophic community is dominated by ‘Ranunculus fluitans’. Primary production parallels the variations of total solar radiations. It ranges from 0 in winter to 8 g O2 m−2 d−1 in summer. In spring and summer, respiration variations parallel those of primary production (average value: 10 g O2 m−2 d−1); in the dry autumn, decomposition of dying macrophytes considerably enhances the community respiration (15 g O2 m−2 d−1). A P/R diagram is used to characterize the trophic state of the Viroin.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1573-5117
    Keywords: river Mosel ; ecological modelling ; oxygen budget ; P vs R ratio ; phytoplankton decline
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The oxygen budget in the transboundary river Mosel was analyzed with the help of the RIVERSTRAHLER model. The model, developed for the river Seine, was used after minor modifications of the kinetics of microbial processes. The impact of benthic filter feeders (Dreissena polymorpha) was introduced into the model to better explain phytoplankton decline in the canalized sector of the river. Hydro-geomorphology, meteorology and point and non-point sources of nutrients were analyzed as required by the model, according to the stream order concept at the scale of the whole drainage network of the main tributaries and along the main branch of the river Mosel, from Millery to Koblenz. The model was validated on water quality data (phytoplankton biomass -Chl a-, nutrients, oxygen) collected at half-monthly intervals during the period 1993–1995. A reasonable agreement was found at both the seasonal and spatial scales. The validated model was used to calculate the oxygen budget that shows variations in the contributions of biological processes (net primary production, bacterial and benthic respiration, nitrification) along successive stretches of the main river branch. Bacterial respiration dominates in sectors particularly affected by effluent inputs. Benthic filter feeders colonising these canalized sectors contribute to increases in respiration and oxygen deficit through their own respiration and their impact on phytoplankton. Several possible management scenarios, aimed at improving oxygenation, were tested with the model. An 80% reduction of both phosphates (to reduce eutrophication) and organic matter (to decrease bacterial activity) restores autotrophic conditions in the 7th order sector.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Aquatic ecology 7 (1973), S. 60-68 
    ISSN: 1573-5125
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Resume L'étude des transformations du mercure dans l'eau et les sédiments d'une rivière est entreprise selon un mode d'approche qui semble pouvoir être généralisé pour de nombreux problème d'écologie chimique. Il consiste en l'utilisation de deux paramètres physicochimiques pour caractériser le milieu du point de vue chimique (l'utilisation de diagramme Eh−pH permettant de prévoir le comportement chimique d'un élément dans le milieu étudié) et du point de vue biologique (le Eh et le pH permettant de caractériser de façon biologiquement significative les conditions dans lesquelles sont testées les capacités de transformation des communautés bactériennes). Il est montré que le comportement du mercure, après son accumulátion sous forme peu soluble dans les sédiments, dépend d'une balance entre la formation microbiologique de méthylmercure, beaucoup plus toxique que le mercure minéral, et la minéralisation de ce méthylmercure par action microbiologique ou par un processus chimique en présence de sulfure.
    Type of Medium: Electronic Resource
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  • 10
    Publication Date: 2022-05-25
    Description: Author Posting. © Ecological Society of America, 2011. This article is posted here by permission of Ecological Society of America for personal use, not for redistribution. The definitive version was published in Frontiers in Ecology and the Environment 9 (2011): 18–26, doi:10.1890/100008.
    Description: Nutrient fluxes to coastal areas have risen in recent decades, leading to widespread hypoxia and other ecological damage, particularly from nitrogen (N). Several factors make N more limiting in estuaries and coastal waters than in lakes: desorption (release) of phosphorus (P) bound to clay as salinity increases, lack of planktonic N fixation in most coastal ecosystems, and flux of relatively P-rich, N-poor waters from coastal oceans into estuaries. During eutrophication, biogeochemical feedbacks further increase the supply of N and P, but decrease availability of silica – conditions that can favor the formation and persistence of harmful algal blooms. Given sufficient N inputs, estuaries and coastal marine ecosystems can be driven to P limitation. This switch contributes to greater far-field N pollution; that is, the N moves further and contributes to eutrophication at greater distances. The physical oceanography (extent of stratification, residence time, and so forth) of coastal systems determines their sensitivity to hypoxia, and recent changes in physics have made some ecosystems more sensitive to hypoxia. Coastal hypoxia contributes to ocean acidification, which harms calcifying organisms such as mollusks and some crustaceans.
    Description: Funding was supplied in part by NOAA through the Coastal Hypoxia Research Program, by the NSF through the Biocomplexity Coupled Biogeochemical Cycles competition, and by DR Atkinson through an endowment given to Cornell University.
    Repository Name: Woods Hole Open Access Server
    Type: Article
    Format: application/pdf
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