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31.
32.
In many tidal embayments, bottom patterns, such as the channel-shoal systems of the Wadden Sea, are observed. To gain understanding
of the mechanisms that result in these bottom patterns, an idealized model is developed and analyzed for short tidal embayments.
In this model, the water motion is described by the depth- and width-averaged shallow water equations and forced by a prescribed
sea surface elevation at the entrance of the embayment. The bed evolves due to the divergence and convergence of suspended
sediment fluxes. To model this suspended-load sediment transport, the three-dimensional advection–diffusion equation is integrated
over depth and averaged over the width. One of the sediment fluxes in the resulting one-dimensional advection–diffusion equation
is proportional to the gradient of the local water depth. In most models, this topographically induced flux is not present.
Using standard continuation techniques, morphodynamic equilibria are obtained for different parameter values and forcing conditions.
The bathymetry of the resulting equilibrium bed profiles and their dependency on parameters, such as the phase difference
between the externally prescribed M2 and M4 tide and the sediment fall velocity, are explained physically. With this model, it is then shown that for embayments that
are dominated by a net import of sediment, morphodynamic equilibria only exist up to a maximum embayment length. Furthermore,
the sensitivity of the model to different morphological boundary conditions at the entrance of the embayment is investigated
and it is demonstrated how this strongly influences the shape and number of possible equilibrium bottom profiles. This paper
ends with a comparison between the developed model and field data for the Wadden Sea’s Ameland and Frisian inlets. When the
model is forced with the observed M2 and M4 tidal constituents, morphodynamic equilibria can be found with embayment lengths similar to those observed in these inlets.
However, this is only possible when the topographically induced suspended sediment flux is included. Without this flux, the
maximum embayment length for which morphodynamic equilibria can be found is approximately a third of the observed length.
The sensitivity of the model to the topographically induced sediment flux is discussed in detail. 相似文献
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35.
Sílvia Santos Joana F.M.F. Cardoso Célia Carvalho Pieternella C. Luttikhuizen Henk W. van der Veer 《Estuarine, Coastal and Shelf Science》2011
Monthly investment in soma and gonads in the bivalve Scrobicularia plana is described for three populations along its distributional range: Minho estuary, Portugal; Westerschelde estuary, The Netherlands and Buvika estuary, Norway. Seasonal cycles in body mass (BMI), somatic mass (SMI) and gonadal mass (GMI) indices were observed for all populations. In Portugal, BMI and SMI peaked in mid-autumn, while in The Netherlands both indices were at their highest in mid-spring. Norway showed a different pattern with two distinct peaks: one in mid-autumn and a second peak in spring. GMI reached maximum values in July in Portugal and Netherlands and in June in Norway. Overall, mean BMI and SMI were lower in Portugal while mean GMI was lower in Norway. The spawning period lasted the whole summer in Portugal, but was shorter (only two months) in The Netherlands and Norway. The reproductive investment in The Netherlands was significantly higher than in Portugal and Norway, with the lowest values being observed in Norway. Differences in annual cycles between populations were attributed to environmental factors, namely temperature and food availability. Temperature seems important in shaping the reproductive pattern with more northern populations showing shorter reproductive periods starting later in the year, and a lower reproductive output. In addition, winter water temperatures can explain the lower mean body and somatic mass values observed in Portugal. Food availability influenced the physiological performance of the species with peaks in somatic mass coinciding with phytoplankton blooms. This relation between physiological performance and environmental factors influences S. plana distribution, densities and even survival, with natural consequences on its commercial importance. 相似文献
36.
Suzanne?E.?HollinsEmail author Jennifer?J.?Harrison Brian?G.?Jones Atun?Zawadzki Henk?Heijnis Stuart?Hankin 《Journal of Paleolimnology》2011,46(4):579-596
In this study, we combined grain size and geochemical analyses with radioisotope analysis of lead-210 (210Pb), caesium-137 (137Cs) and radiocarbon (14C) ages to reconstruct the sedimentation history of two urbanised coastal lagoons in south-east Australia. Towradgi and Fairy
Lagoons were both found to exhibit slow initial sedimentation of less than 1 mm year−1 prior to anthropogenic influences. Land clearing in the catchments increased runoff and erosion in the creeks feeding into
the estuaries, and has resulted in progradation of fluvial material into the estuarine systems with a marked increase in sedimentation
to between 2 and 7 mm year−1. The upper 20–50 cm of the sediment column in both lagoons contained elevated concentrations of heavy metals such as Pb,
Cu, Ni and Zn. This pollution trend was found to be consistent with the history of industrialisation and urbanisation in the
region, which expanded rapidly post World War 2. The total metal concentrations were consistent with other urbanised/industrialised
estuaries around the world. Despite the fairly disturbed nature of these coastal lagoons, the use of 210Pb, 137Cs and 14C dating in combination with bulk geochemical analyses allowed detailed reconstruction of sedimentation history. 相似文献
37.
C. M. Aruffo A. Rodriguez-herrera E. Tenthorey F. Krzikalla J. Minton A. Henk 《Australian Journal of Earth Sciences》2013,60(7):987-1001
This paper presents the first published 3D geomechanical modelling study of the CO2CRC Otway Project, located in the state of Victoria, Australia. The results of this work contribute to one of the main objectives of the CO2CRC, which is to demonstrate the feasibility of CO2 storage in a depleted gas reservoir. With this aim in mind, a one-way coupled flow and geomechanics model is presented, with the capability of predicting changes to the in situ stress field caused by changes in reservoir pressure owing to CO2 production and injection. A parametric study investigating the pore pressures required to reactivate key, reservoir-bounding faults has been conducted, and the results from the numerical simulation and analytical analysis are compared. The numerical simulation indicates that the critical pore fluid pressure to cause fault reactivation is 1.15 times the original pressure as opposed to 1.5 times for the comparable analytical model. Possible reasons for the differences between the numerical and analytical models can be ascribed to the higher degree of complexity incorporated in the numerical model. Heterogeneity in terms of lateral variations of hydrological and mechanical parameters, effect of topography, presence of faults and interaction between cells are considered to be the main sources for the different estimation of critical pore pressure. The numerical model, which incorporates this greater complexity, is able then to better describe the state of stress that acts in the subsurface compared with a simple 1D analytical model. Moreover, the reactivation pressures depend mainly on the state of stress described; therefore we suggest that numerical models be performed when possible. 相似文献
38.
Eric Deleersnijder Emmanuel Hanert Hans Burchard Henk A. Dijkstra 《Ocean Dynamics》2008,58(3-4):237-246
Occasionally, numerical simulations using local turbulence closure schemes to estimate vertical turbulent fluxes exhibit small-scale oscillations in space, causing the eddy coefficients to vary over several orders of magnitude on short distances. Theoretical developments suggest that these spurious oscillations are essentially due to the way the eddy coefficients depend on the vertical gradient of the model’s variables. An instability criterion is derived based on the assumptions that the artefacts under study are due to the development of small-amplitude, small time- and space-scale perturbations of a smooth solution. The relevance of this criterion is demonstrated by applying it to a series a closure schemes, ranging from the Pacanowski–Philander formulas to the Mellor–Yamada level 2.5 model. 相似文献
39.
Marianne Alunno-Bruscia Henk W. van der Veer Sebastiaan A.L.M. Kooijman 《Journal of Sea Research》2009,62(2-3):43
The European Research Project AquaDEB (2007–2011, http://www.ifremer.fr/aquadeb/) is joining skills and expertise of some French and Dutch research institutes and universities to analyse the physiological flexibility of aquatic organisms and to link it to ecological and evolutionary processes within a common theoretical framework for quantitative bioenergetics [Kooijman, S.A.L.M., 2000. Dynamic energy and mass budgets in biological systems. Cambridge University Press, Cambridge]. The main scientific objectives in AquaDEB are i) to study and compare the sensitivity of aquatic species (mainly molluscs and fish) to environmental variability of natural or human origin, and ii) to evaluate the related consequences at different biological levels (individual, population, ecosystem) and temporal scales (life cycle, population dynamics, evolution). At mid-term life, the AquaDEB collaboration has already yielded interesting results by quantifying bio-energetic processes of various aquatic species (e.g. molluscs, fish, crustaceans, algae) with a single mathematical framework. It has also allowed to federate scientists with different backgrounds, e.g. mathematics, microbiology, ecology, chemistry, and working in different fields, e.g. aquaculture, fisheries, ecology, agronomy, ecotoxicology, climate change. For the two coming years, the focus of the AquaDEB collaboration will be in priority: (i) to compare energetic and physiological strategies among species through the DEB parameter values and to identify the factors responsible for any differences in bioenergetics and physiology; and to compare dynamic (DEB) versus static (SEB) energy models to study the physiological performance of aquatic species; (ii) to consider different scenarios of environmental disruption (excess of nutrients, diffuse or massive pollution, exploitation by man, climate change) to forecast effects on growth, reproduction and survival of key species; (iii) to scale up the models for a few species from the individual level up to the level of evolutionary processes. 相似文献
40.
Joana F.M.F. Cardoso Johannes IJ. Witte Henk W. van der Veer 《Estuarine, Coastal and Shelf Science》2009
Cerastoderma edule and Mya arenaria are two common bivalve species in European waters. Longevity and maximum size are much greater in the latter species. Because comparison of species life-history strategies states that a long life span (i.e. high annual survival) generally goes with lower fecundity, we hypothesise that reproductive output would be lower in M. arenaria than in C. edule. In the present paper, we studied the reproductive strategies of these two species in an intertidal and a subtidal area of the western Dutch Wadden Sea, by following seasonal changes in absolute and relative weights of somatic and gonadal tissues in these bivalves. Starting of spawning was similar in the two species, around May, except for intertidal M. arenaria, which initiated spawning in August. Individual energy investment in reproduction was similar for the two species but, unlike M. arenaria, C. edule spawned completely, releasing all energy of gonadal mass in the form of gametes. Mya arenaria used the gonad not only for reproduction but also for storage. In the intertidal area, we found a trade-off between longevity and reproduction, i.e. maximum reproductive output (expressed as a proportion of body mass) was higher in C. edule than in M. arenaria. However, since body size is larger and life span longer in M. arenaria than in C. edule, mean lifetime reproductive output per individual must be higher in the first than in the latter. Based on the differences in reproductive strategies of these two species, we hypothesise that the negative effects of warming climate on bivalve population dynamics in the Wadden Sea will be stronger in C. edule than in M. arenaria. 相似文献