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The experimental study of the hydrodynamics of the sediments and the physical analysis of the process of exchange at the water-sediment interface in a zone of swash are essential for the understanding of the sedimentary transport processes in coastal environments, in particular to control and forecast the evolution of the coastline. The objective of this study was to exploit the technique of Ultrasonic Doppler Velocimetry (UDV) to examine the evolution of the velocity field at the water-sediment interface in a zone of swash in various conditions of incidental regular waves in a wave flume. The velocities were measured in different conditions of the swash within the sediment bed, and in the fluid vein at the swash edge. These measurements show: an exponential distribution of velocities inside the sediment bed; a difference in the velocity gradient at the water-sediment interface, between the velocity in the water vein at the swash edge and the interstitial flow in the swash. The measurements obtained in the wave flume made it possible to observe an evolution of the velocity profiles according to the phases of the swash, which are characterized by a phase shift between the free flow at the swash edge and the interstitial flow during the two phases of the swash: uprush and backwash. 相似文献
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To reduce the complexity and save computation time, an isotropic and a scalar dispersion model are explored and compared to the anisotropic advection/dispersion model to study the interstitial flow in a stream and lake sediment induced by a periodic pressure wave. In these systems, the solute transport is controlled by the ratio (R = a/(LS)) of the pressure wave steepness (a/L) to the stream slope (S), and the dispersivity ratio (λ = αL/L) that measures the longitudinal dispersivity (αL) relative to the pressure wave length (L). Through a series of numerical experiments, the conclusion is reached that a scalar dispersion model can be applied with satisfactory results for advection-dominated transport, i.e. when R ? 0.1 and λ ? 0.01, or λ ? 0.0001, i.e. Peclet number (Pe) ? 10000; an isotropic dispersion model can be applied when R ? 10 or λ ? 0.001, and the full anisotropic advection/dispersion model has to be applied when R > 10 and λ > 0.001. 相似文献
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Interstitial water and hydrochemistry of a mangrove forest and adjoining water system, south west coast of India 总被引:1,自引:0,他引:1
Eh, pH, salinity, total alkalinity, dissolved O2, NO2
–, PO4
–3, SiO2 and NH4
+ of waters from a mangrove forest, an estuary and a creek connecting the mangrove forest and the estuary have been measured.
Further, the chemistry of interstitial waters of surficial and core sediments from the mangrove forest have been analyzed
for the above parameters, except dissolved oxygen. To understand the flux of nutrients from the mangrove forest to the adjoining
estuary, creek waters were monitored during tidal phases. PO4
–3, SiO2 and NH4
+ were found to be at elevated levels in mangrove waters whereas NO2
– shows no variation compared to the estuary. Dissolved O2 is low in mangrove waters. PO4
–3, NH4
+ and SiO2 are several times higher in interstitial waters than in overlying waters. Several fold enrichment of PO4
–3, NH4
+ and, to some extent, SiO2 were measured in creek waters during ebbing relative to flooding, indicating that mangroves act as a perennial source for
the above nutrients.
Received: 26 May 1998 · Accepted: 21 July 1998 相似文献
16.
The concentrations of N, P and Fe in surface sediments and interstitial and overlying (bottom and surface) waters of the
Ashtamudi estuary located in the southwest coast of India are reported along with the various chemical species of N (NO2–N, NO3–N, NH3–N and total N) and P (organic P, inorganic P and total P) in interstitial and overlying waters and discussed in terms of
the physico-chemical environment of the system. The interstitial water exhibits higher salinity values compared to bottom
and surface waters, indicating the coupled effects of salt-wedge phenomena and gravitational convection of more saline-denser
marine water downward through surface sediments. N, P and Fe as well as their chemical forms are enriched in the interstitial
water compared to bottom and surface waters. However, the dissolved oxygen (DO) shows an opposite trend. The marked enrichment
of NH3–N in the interstitial water and its marginal presence in bottom and surface waters, together with the substantial decrease
in the DO concentrations of bottom water and consequent increase in the concentrations of NO2–N and NO3–N in interstitial and bottom waters, points to the nitrification process operating in the sediment-water interface of the
Ashtamudi estuary. The enrichment of total N, P and Fe in the interstitial water compared to the overlying counterparts and
the positive correlation of sediment N, P and Fe with mud contents as well as organic carbon indicate that these elements
are liberated during the early diagenetic decomposition of organic matter trapped in estuarine muds.
Received: 5 Oktober 1998 · Accepted: 9 February 1999 相似文献
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Hans Jürgen Hahn 《Limnologica》2003,33(2):138-146
In the sediments of a southwestern German headwater, pumping and two types of unbaited traps were compared with respect to their suitability for the sampling of interstitial meiofauna. The aim of the study was to discover whether the type-2 trap, having been developed for universal use, could be utilised in the hyporheic zone, as well as in groundwater. Trap samples demonstrate both greater abundance and taxonomic richness than those samples obtained by pumping, though very few differences could be detected between the two types of trap. The taxonomic composition, however, was found to be very similar for all three sampling methods. Other researchers also observed a high similarity of stygofaunal communities between pumped groundwater and the water of the bores, which act as traps. This would imply that not only do trap samples as well or better reflect community structure of the surrounding sediment than does pumping, but also that the type-2 trap is, indeed, suitable for the sampling of meiofauna in both the hyporheic zone and in groundwater. 相似文献
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