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Registros recuperados: 35
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A model of early diagenetic processes from the shelf to abyssal depths OMA
Soetaert, K.; Herman, P.M.J.; Middelburg, J.J..
We present a numerical model of sedimentary early diagenetic processes that includes oxic and anoxic mineralization. The model belongs to the new wave of early diagenesis models that account for depth-dependent bioturbation and porosity profiles; it can be used both for calculating steady-state conditions and transient simulation. It was developed to reproduce the cycling of carbon, oxygen, and nitrogen along the ocean margin; it resolves the sediment-depth profiles of carbon, oxygen, nitrate, ammonium, and other reduced substances. Organic carbon is modeled as two degradable fractions with different first-order degradation rates and nitrogen:carbon ratios, to account for the decreasing reactivity and N/C ratio of the organic matter with depth into the...
Tipo: Info:eu-repo/semantics/article
Ano: 1996 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8408
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A model of nematode dynamics in the Westerschelde Estuary OMA
Li, J.; Vincx, M.; Herman, P.M.J..
We developed a time dynamic model to investigate the temporal dynamics of nematode community in the brackish zone of the Westerschelde Estuary. The biomass of four nematode feeding groups observed from March 1991 to February 1992 is used to calibrate the model. Using environmental data as the input, the model predicts the temporal modification and interrelation of four nematode feeding groups. Nematodes achieve a dominant position in the community because of their lower loss rate (in respiration, excretion and natural death). Predators which are deposit-feeding macrobenthos control the variations of dominant nematodes, such as omnivores and non-selective deposit feeders. Food availability causes modification only for rare nematodes such as epigrowth...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Diatoms; Ecology; Food; Light; Marine nematodes; Meiobenthos; Population dynamics; Predation; Respiration; Temperature; Nematoda [Nematodes].
Ano: 1996 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=7284
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A re-evaluation of marine nematode productivity OMA
Vranken, G.; Herman, P.M.J.; Vincx, M.; Heip, C.H.R..
Nematodes are the most abundant multicellular animals in marine sediments but their role in the benthos has not been properly quantified yet. In nearly all energy-flow budgets of marine systems their annual production P is given as about nine times their biomass B and their part in the total energy-flow is consequently estimated as anywhere between 3 and 30% of the total (carbon) input in the benthic system. Our laboratory experiments demonstrate that nematode productivity is much higher than P/B ~ 9 per year and may reach values of over 60 for bacterial grazers. To obtain more reliable estimates for field populations we propose a regression equation relating egg-to-egg development time T<sub>min</sub> to temperature (t) and adult female weight...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Biological production; Mathematical models; Meiobenthos; Nematoda [Nematodes].
Ano: 1986 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=3576
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Analysis of community attributes of the benthic meiofauna of Frierfjord-Langesundfjord OMA
Heip, C.H.R.; Warwick, R.M.; Carr, M.R.; Herman, P.M.J.; Huys, R.; Smol, N.; Van Holsbeke, K..
Tipo: Info:eu-repo/semantics/article
Ano: 1988 URL: http://www.vliz.be/imisdocs/publications/221038.pdf
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Assessing organic matter mineralization, degradability and mixing rate in an ocean margin sediment (Northeast Atlantic) by diagenetic modeling OMA
Soetaert, K.; Herman, P.M.J.; Middelburg, J.J.; Heip, C.H.R..
We test whether organic matter degradability, mixing activity, and total sediment mineralization can be estimated by inversion of a coupled nonlinear numerical steady-state diagenetic model. We use a single data set comprising oxygen, nitrate, ammonium and organic carbon versus depth profiles from a slope station in the Goban Spur area (1034 m, Northeast Atlantic). Based on an extensive sensitivity analysis, it appears that (1) when using all data, the total mineralization rates can be determined with reasonable precision; bioturbation and degradability are less well constrained and (2) total mineralization rates can be determined based on nitrate and oxygen profiles only; estimates of organic matter mixing rates and degradability are refined when...
Tipo: Info:eu-repo/semantics/article
Ano: 1998 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8426
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Bodemdieren langsheen estuariene gradiënten OMA
Ysebaert, T.; Herman, P.M.J..
Tipo: Info:eu-repo/semantics/article
Ano: 2001 URL: http://www.vliz.be/imisdocs/publications/280704.pdf
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Carbon flows in the Westerschelde estuary (The Netherlands) evaluated by means of an ecosystem model (MOSES) OMA
Soetaert, K.; Herman, P.M.J..
The autotrophic production and heterotrophic consumption of organic matter in the Westerschelde, a highly turbid and eutrophic estuary in the Southwest Netherlands is examined by means of a dynamic simulation model. The model describes the ecologically relevant processes in thirteen spatial compartments and adequately fits most observed data. Three autotrophic processes are included in the model. Net pelagic photosynthetic production is relatively low (average 41 gC m<sup>-2</sup> yr<sup>-1</sup>) and three spatial compartments near the turbidity maximum zone are respiratory sinks of phytoplankton biomass. According to the model, net phytobenthic primary production is more important than pelagic primary production in the upstream...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Autotrophy Carbon Carbon cycle Estuaries Estuarine dynamics Eutrophication Heterotrophy Mathematical models Mineralization Photosynthesis Primary production Trophic relationships ANE; Netherlands; Westerschelde.
Ano: 1995 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8417
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Carbon flows through meiobenthic nematodes in the Westerschelde Estuary IRD
Li, J.; Vincx, M.; Herman, P.M.J..
Un modèle en temps dynamique a été utilisé pour évaluer le flux de carbone chez les nématodes appartenant à un écosystème benthique intertidal de l'estuaire de l'Escaut occidental, aux Pays-Bas. Le modèle a permis de calibrer la biomasse des nématodes de mars 1991 à février 1992. Les fonctions de contrainte du modèle incluent la biomasse du meiobenthos, celle du macrobenthos, la concentration en bactéries, la concentration en chlorophylle a, et d'autres paramètres de l'environnement, tels la température et la photopériode. Il est estimé que la population de nématodes présents a un faible niveau de stock, 249 mb C/m2, mais un niveau élevé de flux de carbone. Les nématodes consomment 98 mg C/m2/d et produisent 22 mg C/m2/d. La défécation est de 73 C/m2/d....
Tipo: Text Palavras-chave: NEMATODE; BENTHOS; BIOMASSE; CARBONE; MATIERE ORGANIQUE; PRODUCTIVITE.
Ano: 1997 URL: http://www.documentation.ird.fr/hor/fdi:010012347
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Carbon flows through meiobenthic nematodes in the Westerschelde Estuary OMA
Li, J.; Vincx, M.; Herman, P.M.J..
A time dynamic model was used to estimate carbon flows through nematodes in an intertidal benthic ecosystem in the Westerschelde Estuary, The Netherlands. The model calibrated the nematode biomass observed from March 1991 to February 1992. The forcing functions of the model included meiobenthos biomass, macrobenthos biomass, bacterial density, chlorophyll-a concentration, and other abiotic data such as temperature and day length. We estimate that the nematode population had a low level of standing stock 249 mg C m(-2), but a high level of carbon flow. It consumed 98 mg C m(-2) d(-1) and produced 22 mg C m(-2) d(-1). Defecation was 73 mg C m(-2) d(-1). Losses in respiration, excretion and natural death were only 3 mg C m(-2) d(-1). The annual P/B was 32 for...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Degradation; Ecology; Marine nematodes; Meiobenthos; Respiration.
Ano: 1997 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=7296
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Denitrification in marine sediments: a model study OMA
Middelburg, J.J.; Soetaert, K.; Herman, P.M.J.; Heip, C.H.R..
The rate and factors controlling denitrification in marine sediments have been investigated using a prognostic diagenetic model. The model is forced with observed carbon fluxes. bioturbation and sedimentation rates, and bottom water conditions. It can reproduce rates of aerobic mineralization, denitrification, and fluxes of oxygen, nitrate, and ammonium. The globally integrated rate of denitrification is estimated by this model to be about 230-285 Tg N yr<sup>-1</sup>, with about 100 Tg N yr<sup>-1</sup> occurring in shelf sediments. This estimate is significantly higher than literature estimates (12-89 Tg N yr<sup>-1</sup>), mainly because of a proposed upward revision of denitrification rates in slope and deep-sea...
Tipo: Info:eu-repo/semantics/article
Ano: 1996 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8415
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Dynamic response of deep-sea sediments to seasonal variations: a model OMA
Soetaert, K.; Herman, P.M.J.; Middelburg, J.J..
We present a dynamic, numerical model of early diagenetic processes that can be used to examine the response of different organic carbon mineralization pathways, concentration vs. depth profiles, and the resultant fluxes to seasonally varying carbon deposition. We show that there can be substantial temporal variability in sediment-water fluxes as well as in the relative contribution of different organic carbon mineralization pathways and oxygen consumption processes in deep-sea sediments. The timing and amplitude of the sediment response are most sensitive to the reactivity of the organic matter. We show that the fluxes of dissolved substances can be approximated by assuming that these constituents are at steady state with the carbon profiles. The model is...
Tipo: Info:eu-repo/semantics/article
Ano: 1996 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8444
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Estimating estuarine residence times in the Westerschelde (The Netherlands) using a box model with fixed dispersion coefficients OMA
Soetaert, K.; Herman, P.M.J..
The residence time of the water masses in the Westerschelde estuary was determined using a simple compartment-model that simulates the advective-diffusive transport of a conservative dissolved substance (chlorinity). The residence time of a water parcel in the upstream part of the estuary (i.e. the time needed for this water parcel to leave the estuary) varied from about 50 days in winter to about 70 days in summer. The most seaward compartment had residence times of about 10-15 days. Dispersive coefficients that are fixed in time were able to reproduce the observed salinity distributions very well in the Westerschelde. They were obtained by calibration on observed chlorinities. It is argued that the apparent relationship of dispersive coefficients with...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Diffusion coefficients Environmental monitoring Estuarine dynamics Mathematical models Residence time Salinity profiles Water circulation ANE; Netherlands; Westerschelde.
Ano: 1995 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8410
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Eten en gegeten worden in het Schelde-estuarium OMA
Moens, T.; Herman, P.M.J.; Ysebaert, T.J..
Tipo: Info:eu-repo/semantics/article
Ano: 2001 URL: http://www.vliz.be/imisdocs/publications/280698.pdf
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Growth and respiration of <i>Cyprideis torosa</i> Jones 1850 (Crustacea Ostracoda) OMA
Herman, P.M.J.; Heip, C.H.R..
The ostracod <i>Cyprideis torosa</i> Jones 1850 is a dominant species in brackish water habitats. To assess its importance, growth and respiration were measured. The shells form an increasing part of total weight as the animals grow but there is no correlation between shell weight and soft parts weight in the adults, indicating that tissue growth is a continuous process in these ostracods. Respiration was measured at 20 °C. The slope of the log-log regression of respiration on dry weight was 0.746, showing that <i>Cyprideis torosa</i> follows the general rule for this relationship. The respiration rate per unit biomass was 0.246 nl O<sub>2</sub> µg<sup>-1</sup> h<sup>-1</sup>, which is low but...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Growth; Respiration; Cyprideis torosa.
Ano: 1982 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=3382
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Living in the twilight: estimating net phytoplankton growth in the Westerschelde estuary (The Netherlands) by means of an ecosystem model (MOSES) OMA
Soetaert, K.; Herman, P.M.J.; Kromkamp, J..
Net phytoplankton productivity in the Westerschelde, a relatively deep. highly turbid and eutrophic estuary in the Southwest Netherlands, was examined by means of a 13-compartment dynamic simulation model. The description of the light-Iimited primary production was based on the model of Eilers and Peeters (1988. <i>Ecol. Model.</i>, 42, 185-198). This light limitation was parameterized to the different model compartments by integrating the Eilers-Peeters model over a day and over depth taking into account the morphology of the Westerschelde compartments, the daily fluctuating light regime and characteristics of the photosynthesis-Iight curves of the phytoplankton community. The availability of light to the phytoplankters limited primary...
Tipo: Info:eu-repo/semantics/article
Ano: 1994 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8464
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Measurement of the adenylate energy charge in <i>Nereis diversicolor</i> and <i>Nephtys</i> sp. (Polychaeta: Annelida): evaluation of the usefulness of AEC in pollution monitoring OMA
Verschraegen, K.; Herman, P.M.J.; Van Gansbeke, D.; Braeckman, A..
ATP-content and adenylate energy charge (AEC) ratios were determined in two polychaete species (<i>Nereis diversicolor</i> and <i>Nephtys</i> sp.), sampled in ten stations along the heavily polluted Western Scheldt estuary (N. Belgium, S. Holland). The samples were taken between 27 December 1982 and 6 January 1983. <i>Nereis diversicolor</i> was also sampled in an unpolluted brackish water pond, and subjected to artificial stress by drying the organisms on filter paper. Adenine nucleotide levels were determined using the firefly bioluminescence reaction. The light emission was measured with the integration mode. As the "Constant Light Signal" reagent used contained APM and probably ADP itself, both myokinase and...
Tipo: Info:eu-repo/semantics/article Palavras-chave: AMP ATP Efficiency Pollution monitoring Annelida [segmented worms] Nephtys Nereis diversicolor [estuary ragworm] Belgium; Zeeschelde.
Ano: 1985 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=3282
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Modeling <sup>210</sup>Pb-derived mixing activity in ocean margin sediments: diffusive versus nonlocal mixing OMA
Soetaert, K.; Herman, P.M.J.; Middelburg, J.J.; Heip, C.H.R.; deStigter, H.S.; van Weering, T.C.E.; Epping, E.; Helder, W..
The influence of sediment mixing on activity versus depth profiles of the radionuclide <sup>210</sup>Pb in the upper 20 cm of the sediments has been investigated along a depth transect (208 m-4500 m, 17 stations) in the OMEX study area (Goban Spur, NE Atlantic Ocean). A hierarchical family of bioturbation/nonlocal exchange models was derived. Each member of the hierarchy includes all processes of the previous model, and adds a one- or two-parameter process. The significance of the additional parameters is tested using a one-tailed <i>F</i>-test. It was found that (1) in five cases there is a significant improvement when direct injection of part of the flux into deeper sediment layers (nonlocal exchange) is added to the diffusive...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Chemical kinetics Continental margins Diffusion Lead 210 Modelling Sediment mixing ANE; Goban Spur.
Ano: 1996 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8450
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Monitoring meiobenthos using cm-, m- and km-scales in the Southern Bight of the North Sea OMA
Li, J.; Vincx, M.; Herman, P.M.J.; Heip, C.H.R..
Tipo: Info:eu-repo/semantics/article
Ano: 1997 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=7297
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Nematode distribution in ocean margin sediments of the Goban Spur (northeast Atlantic) in relation to sediment geochemistry OMA
Soetaert, K.; Vanaverbeke, J.; Heip, C.H.R.; Herman, P.M.J.; Middelburg, J.J.; Sandee, A.; Duineveld, G.C.A..
Nematode density along a depth gradient (206-2760 m) in the northeastern Atlantic (Goban Spur) is linearly and positively related to organic matter mineralization in the sediment. It is estimated that nematodes contribute at most 13% to total carbon turnover, and this contribution decreases with water depth. The vertical distribution of nematodes in the sediment closely follows concentration <i>vs</i> depth profiles of total nitrogen in the sediment. Both nematodes and total nitrogen tend to be more concentrated towards the surface with increasing water depth. There is no indication that nematode vertical distribution is directly influenced by the oxygen penetration in the sediment. However, it is hypothesized that the sediment oxygen...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Dissolved oxygen Ecological distribution Food availability Geochemistry Nitrogen Oxic sediments Population density Sediment chemistry Nematoda [Nematodes] ANE; Atlantic; Goban Spur.
Ano: 1997 URL: http://www.vliz.be/nl/open-marien-archief?module=ref&refid=8407
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Nitrogen dynamics in the Westerschelde estuary (SW Netherlands) estimated by means of the ecosystem model MOSES OMA
Soetaert, K.; Herman, P.M.J..
A tentative nitrogen budget for the Westerschelde (SW Netherlands) is constructed by means of a simulation model with thirteen spatial compartments. Biochemical and chemical processes in the water column are dynamically modeled; fluxes of dissolved constituents across the water-bottom interface are expressed by means of diagenetic equations. The model is calibrated on a large amount of observed variables in the estuary (1980-1986) with relatively fine temporal and spatial detail. Additional constraints are imposed by the stoichiometric coupling of carbon, nitrogen and oxygen flows and the required conservation of mass. The model is able to reproduce rather well the observed distributions of nitrate, ammonium, oxygen and Kjeldahl nitrogen both in time and...
Tipo: Info:eu-repo/semantics/article Palavras-chave: Biochemical phenomena Chemical kinetics Denitrification Environmental monitoring Estuaries Mathematical models Nitrification Nitrogen Nitrogen cycle Organic matter Phytoplankton ANE; Netherlands; Westerschelde.
Ano: 1995 URL: http://www.vliz.be/imisdocs/publications/224384.pdf
Registros recuperados: 35
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