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1.
We investigated the vertical and temporal distributions of portunid zoea andCallinectes megalopae in a tidal pass of the Texas coast. Zoea were equally abundant on ebb and flood tide but were more abundant during the day than at night. Megalopae were more abundant during flood tide and at night than during ebb tide or during the day. We examined the evidence for selective tidal stream transport in both life-history stages. Depth of the centers of mass of the larval distributions and the dispersions around those centers were unrelated to temperature, salinity, current velocity, and time of day. Scaling arguments suggest that the absence of pattern in the vertical distributions was not due to turbulent mixing. There was little evidence that either larval stage used these environmental characteristics as cues for changes in behaviour. However, the presence of megalopae in the water column primarily during flood tide does support the tidal transport hypothesis. Megalopae may have difficulty sensing and reacting to environmental cues in wellmixed estuaries with semidiurnal tides. 相似文献
2.
Fluvial to tidal transition in proximal,mixed tide‐influenced and wave‐influenced deltaic deposits: Cretaceous lower Sego Sandstone,Utah, USA 
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下载免费PDF全文 Marijn van Cappelle Stephen Stukins Gary J. Hampson Howard D. Johnson 《Sedimentology》2016,63(6):1333-1361
Facies models for regressive, tide‐influenced deltaic systems are under‐represented in the literature compared with their fluvial‐dominated and wave‐dominated counterparts. Here, a facies model is presented of the mixed, tide‐influenced and wave‐influenced deltaic strata of the Sego Sandstone, which was deposited in the Western Interior Seaway of North America during the Late Cretaceous. Previous work on the Sego Sandstone has focused on the medial to distal parts of the outcrop belt where tides and waves interact. This study focuses on the proximal outcrop belt, in which fluvial and tidal processes interact. Five facies associations are recognized. Bioturbated mudstones (Facies Association 1) were deposited in an offshore environment and are gradationally overlain by hummocky cross‐stratified sandstones (Facies Association 2) deposited in a wave‐dominated lower shoreface environment. These facies associations are erosionally overlain by tide‐dominated cross‐bedded sandstones (Facies Association 4) interbedded with ripple cross‐laminated heterolithic sandstones (Facies Association 3) and channelized mudstones (Facies Association 5). Palaeocurrent directions derived from cross‐bedding indicate bidirectional currents which are flood‐dominated in the lower part of the studied interval and become increasingly ebb‐directed/fluvial‐directed upward. At the top of the succession, ebb‐dominated/fluvial‐dominated, high relief, narrow channel forms are present, which are interpreted as distributary channels. When distributary channels are abandoned they effectively become estuaries with landward sediment transport and fining trends. These estuaries have sandstones of Facies Association 4 at their mouth and fine landward through heterolithic sandstones of Facies Association 3 to channelized mudstones of Facies Association 5. Therefore, the complex distribution of relatively mud‐rich and sand‐rich deposits in the tide‐dominated part of the lower Sego Sandstone is attributed to the avulsion history of active fluvial distributaries, in response to a subtly expressed allogenic change in sediment supply and relative sea‐level controls and autocyclic delta lobe abandonment. 相似文献
3.
Jianhua GAO Yang YANG Yaping WANG Shaoming PAN Rui ZHANG 《Frontiers of Earth Science》2008,2(3):249-261
High-resolution current velocity and suspended sediment concentration (SSC) data were collected by using an Acoustic Doppler
Current Profiler (ADCP) at two anchor stations and a cross-section in the South Channel of the Changjiang River mouth during
meso and neap tides on Nov. 16, 2003. In addition, tidal cycle (13-hour) observation at two stations was carried out with
traditional methods during the spring tide. Results indicated that resuspension occurred not only at the flood and ebb maximum,
but also in the early phase of ebb in the meso and neap tide. When tidal current transited from high to ebb phase, current
speed accelerated. Subsequently, fine-grained sediment with low critical threshold was resuspended and increased concentration.
The river mouth area remained in siltation in the meso and neap tidal phase during the observation season, with calculated
resuspension flux in the order of magnitude of 10−4–10−7 kg·m−2/s. Suspended sediment transport in the South Channel was dominated by freshwater discharge, but the Storks drift,
vertical circulation and vertical shear effect due to tidal oscillation also played an important role in resuspension and
associated sediment transport. In contrast, resuspension sediment flux in the spring tide was larger than that in meso and
neap tide, especially at the ebb maximum and flood maximum. The present study revealed that intensive resuspension corresponded
well with the larger current velocity during winter. In addition, the ‘tidal pumping’ effect and tidal gravity circulation
were also vital for forming the turbidity maximum in the Changjiang River estuary. 相似文献
4.
采用大凌河实测长系列河道径流及水下地形等数据, 通过建立水动力数值模型, 综合考虑潮流和河道径流的影响, 对大凌河口的潮流进行模拟, 探讨大凌河口及辽东湾北部海域水动力过程的主要特征. 结果表明: 大凌河口附近海域的海流以潮流为主, 具有明显的往复性质. 潮流总的运动趋势是, 涨潮主流向为北东, 落潮主流向为南西. 大潮流速大于小潮流速, 涨潮流历时与落潮流历时几乎相当. 最大涨潮流速约为0.52 m/s, 最大落潮流速约为0.4 m/s, 潮流涨落平均潮流强度的分布大体和该海域等深线相适应. 相似文献
5.
Surface films on marsh creeks form water-air interfaces of high biological activity. The development, movement, deposition, and breakup of the tidal creek surface film in a naturalSpartima alterniflora-dominated salt marsh in Delaware were followed seasonally over tidal cycles. The metabolic activity, i.e., photosynthesis and respiration, of the surface film and underlying water were determined in the field at the time of peak film formation, just prior to high tide, and the particulate material and chlorophylla were quantified over the tidal cycles. The quantities of organic and inorganic components of the particulate material were all significantly higher in the surface film than in the underlying water (on a volume basis). Numbers of algal cells and quantities of chlorophyll were orders of magnitude greater in the surface film than in the water column. Photosynthesis and respiration were significantly higher in the surface film than in the underlying water. The spectrum of fatty acids was more diverse and their total content was significantly greater in the surface film than in the water column, indicating a concentrated food source contributed by the film as well as a biological richness of the film. When water in the creek flooded the marsh plain at high tide, film deposition was greatest on simulated creek bankS. alterniflora stems, compared to stems along rivulets in the marsh and those in the marsh plain. Using surface film dry weight measurements on an areal basis and film velocity in the creek, both measured throughout a tidal cycle during the summer, it was determined that approximately 12 kg (dry weight) of particulate material moved on the creek surface (2 m wide) past a given point on the flood tide, and 14 kg moved in the opposite direction on the ebb tide. The biological and physical data collected in this study illuminate the contribution of the surface film to the biological (food web) and physical (sediment transport and deposition) functions of a salt marsh. 相似文献
6.
Freshwater fraction and tidal prism models are simple methods for estimating the turnover time of estuarine water. The freshwater
fraction method prominently features flushing by freshwater inflow and has sometimes been criticized because it appears not
to include flushing by seawater, but this is accounted for implicitly because the average estuary salinity used in the calculation
reflects all the processes that bring seawater into the estuary, including gravitational circulation and tidal processes.
The model relies on measurable salinity differences among water masses and so must be used for estuaries with substantial
freshwater inflow. Tidal prism models are based on flushing by flood tide inflow and ignore seawater inflow due to gravitational
circulation. These models should only be applied to estuaries with weak or nonexistent gravitational circulation, which are
generally those with little freshwater inflow. Using a framework that is less ambioguous and more directly applicable to the
estimation of turnover times than those used previously, this paper critically examines the application of tidal prism models
in well-mixed estuaries with complete tidal exchange, partial ebb return, or incomplete flood mixing and in partially mixed
estuaries. Problems with self-consistency in earlier versions of these models also apply to the budgeting procedure used by
the LOICZ (Land-Ocean Interactions in the Coastal Zone) program. Although freshwater fraction and tidal prism models are different
approaches to estimating turnover times in systems with very different characteristics, consistent derivation shows that these
models have much in common with each other and that they yield equivalent values that can be used to make comparisons across
systems. 相似文献
7.
为更合理选取涌潮河口的底摩擦系数,基于无结构三角网格和有限体积法,建立了适用于反演潮汐涌潮河口底摩擦系数随空间和涨、落潮变化的伴随资料同化模型。一系列"孪生"实验均较精确地反演出了给定底摩擦系数。孪生实验表明底摩擦系数的空间分布会影响反演的精度,也表明充足的观测数据资料能够提高反演的准确性。利用实测数据进行了钱塘江河口伴随同化实验,得到涨、落潮底摩擦系数分别为0.000149和0.001520(相当于曼宁系数为0.012206和0.038987),利用该值模拟出了潮波变形和涌潮形成等现象,验证了前人在钱塘江河口数值模拟时关于底摩擦系数选取经验的合理性,反映了钱塘江河口底摩擦"涨小落大"的实质。 相似文献
8.
0-group sea bass,Dicentrarchus labrax, colonize intertidal marsh creeks of Mont Saint Michel Bay, France, on spring tides (e.g., 43% of the tides) during flood
and return to coastal waters during ebb. Most arrived with empty stomachs (33%), and feed actively during their short stay
in the creeks (from 1 to 2 h) where they consumed on average a minimum of 8% of their body weight. During flood tide, diet
was dominated by mysids,Neomysis integer, which feed on marsh detritus. During ebb, when young sea bass left tidal marsh creeks, the majority had full stomachs (more
than 98%) and diet was dominated by the most abundant marsh (including vegetated tidal flats and associated marsh creeks)
resident amphipod,Orchestia gammarellus. Temporal and tidal effects on diet composition were shown to be insignificant. Foraging in vegetated flats occurs very rarely
since they are only flooded by about 5% of the tides. It was shown that primary and secondary production of intertidal salt
marshes play a fundamental role in the feeding of 0-group sea bass. This suggests that the well known nursery function of
estuarine systems, which is usually restricted to subtidal and intertidal flats, ought to be extended to the supratidal, vegetated
marshes and mainly to intertidal marsh creeks. 相似文献
9.
In October of 2004, a 3-d observational program to measure flow and sediment resuspension within a coastal intertidal salt
marsh was conducted in the North Inlet/Winyah Bay National Estuarine Research Reserve located near Georgetown, South Carolina.
Current and acoustic backscatter profiles were obtained from a moored acoustic Doppler current profiler (ADCP) deployed in
a shallow tidal channel during the spring phase of the tidal cycle under high discharge conditions. The channel serves as
a conduit between Winyah Bay, a large brackish estuary, and North Inlet, a saline intertidal coastal salt marsh with little
freshwater input. Salinity measurements indicate that the water column is vertically well mixed during flood, but becomes
vertically stratified during early ebb. The stratification results from brackish (15 psu) Winyah Bay water entering North
Inlet via the tidal channel, suggesting an exchange mechanism that permits North Inlet to receive a fraction of the poor water
quality and high discharge flow from upland rivers. Although maximum flood currents exceed maximum ebb currents by 0.2 m s−1, suspended sediment concentrations are highest during the latter ebb phase and persist for a longer fraction of the ebb cycle.
Even though the channel is flood-dominated, the higher concentrations occurring over a longer fraction of the ebb phase indicate
net particulate transport from Winyah Bay to North Inlet during spring tide accompanied by high discharge. Our evidence suggests
that the higher concentrations during ebb result from increased bed friction caused by flow asymmetries and variations in
water depth in which the highest stresses occur near the end of ebb near low water despite stronger maximum currents during
flood. 相似文献
10.
We examined high frequency fluctuations in water quality parameters in two tropical coastal plain estuaries in response to
changing tidal flow conditions. The variability in total suspended sediments (TSS), volatile suspended solids (VSS), total
organic carbon (TOC) concentrations, and indicators of water quality, including pH, temperature, salinity, and dissolved oxygen,
over one spring tidal cycle during the early wet monsoon season was measured in two estuaries in eastern Sumatra. The relatively
high rainfall experienced throughout the year, in combination with the recent extensive vegetation clearing and modification
of the landscape, resulted in significant concentrations of TSS, VSS, and TOC being discharged to coastal waters. Maximum
values are reached on the ebb tide (TSS > 1,013 mg l−1; VSS > 800 mg l−1; TOC >60 mg l−1). The influence of freshwater discharge and tidal flow on water properties of the lower estuaries is also marked by the variability
in salinity, dissolved oxygen, and pH over the tidal cycle, with minimum values for each of these parameters following maximum
current velocities and after the completion of the strong ebb tide. Estimation of seaward sediment fluxes, which are of significant
interest in a region where rapid environmental change is occurring, would require further examination of sedimentary processes,
such as resuspension and advection of sediment, as well as a consideration of neap-spring tidal variations and the effect
of seasonality on estuarine circulation. 相似文献
11.
The distribution of two classes of lipid biomarker compounds (fatty acids and sterols) was used in conjunction with several
bulk parameters (total suspended solids, chlorophyll a, and particulate carbon and nitrogen concentrations) to examine spatial and temporal variability in the sources of particulate
organic matter (POM) important to southern Chesapeake Bay. Based on these geochemical parameters, we found that suspended
and sedimentary organic matter in the southern Chesapeake Bay is derived from autochthonous sources including a mixture of
fresh and detrital phytoplankton, zooplankton, and bacteria. The dominant factor contributing to temporal variability during
our study was phytoplankton productivity. Enrichments in particulate organic carbon, chlorophyll a, total fatty acids, total sterols, and a number of biomarkers specific to phytoplankton sources were found in particles collected
from surface (1 m) and deep (1 m above the bottom) portions of the water column at several sites during the spring bloom in
March 1996 and during a localized bloom in July 1995. Comparison of sites at the mouths of two tributaries (York and Rappahannock
rivers) to southern Chesapeake Bay with two sites located in the bay mainsterm indicates spatial variation in the composition
of POM was not significant in this region of the bay. The energetic nature of this region of the Chesapeake Bay most likely
contributes to the observed homogeneity. Comparison with biomarker studies conducted in other estuaries suggests the high
levels of productivity characteristic of the Chesapeake Bay contribute to high background levels of POM. 相似文献
12.
We describe the tidal circulation of a coastal plain estuary across a flood tide delta located at its entrance. The area connects
the downstream portion of the main estuary extending 30–40 km inland to the more complex delta reach that consists of a shallow
main channel and a series of smaller side channels. The delta acts as a frictionally dominated zone that modifies the tidal
wave from a simple sinusoid to one with ebb currents that accelerate to maximum early in the tidal cycle and last more than
one-half of the tidal cycle. Along smaller side channels, the tidal currents favor stronger flood or ebb currents, depending
upon the local surrounding morphology. The phase difference between ebb currents in the small channels relative to those in
the main channel cause some of the salt to be retained thus reducing the tendency of freshwater discharge to flush salt out
of the system. This mechanism of retention differs from the selective withdrawal mechanism described for this estuary in Blanton
et al. (2000). 相似文献
13.
Ned P. Smith 《Estuaries and Coasts》1979,2(4):218-227
Current, water level and wind data collected from a study site at the Aransas Pass, Texas, during a 45-day period in mid 1977 are used to describe tidal motions and low-frequency, meteorologically-forced exchanges between the inner shelf and a series of intracoastal bays. Analysis of individual tidal constituents indicates a mixed but principally diurnal tide. Tidal constituents move through the Pass as nearly progressive waves. Asymmetry in the co-oscillating tidal motions is explained as a result of unequal frictional forces acting on flood and ebb currents in the Pass. Tidal excursions computed from the tidal harmonic constants and from cumulative net displacements suggest that tidal-period exchanges are not effective in flushing the bays even under tropic tidal conditions. Nontidal water levels are related to the cross-shelf component of the coastal windstress at statistically significant levels. This suggests that low-frequency local meteorological forcing, as a set-up or set-down of coastal water levels, plays a valuable role in assisting tidally-driven exchanges. 相似文献
14.
We describe the tidal circulation and salinity regime of a coastal plain estuary that connects to the ocean through a flood
tide delta. The delta acts as a sill, and we examine the mechanisms through which the sill affects exchange of estuarine water
with the ocean. Given enough buoyancy, the dynamics of tidal intrusion fronts across the sill and selective withdrawal (aspiration)
in the deeper channel landward appear to control the exchange of seawater with estuarine water. Comparison of currents on
the sill and stratification in the channel reveals aspiration depths smaller than channel depth during neap tide. During neap
tide and strong vertical stratification, seawater plunges beneath the less dense estuarine water somewhere on the sill. Turbulence
in the intruding bottom layer on the sill promotes entrainment of fluid from the surface layer, and the seawater along the
sill bottom is diluted with estuarine water. During ebb flow, salt is effectively trapped landward of the sill in a stagnant
zone between the aspiration depth and the bottom where it can be advected farther upstream by flood currents. During spring
tide, the plunge point moves landward and off the sill, stratification is weakened in the deep channel, and aspiration during
ebb extends to the bottom. This prevents the formation of stagnant water near the bottom, and the estuary is flooded with
high salinity water far inland. The neapspring cycle of tidal intrusion fronts on flood coupled with aspiration during ebb
interacts with the sill to play an important role in the transport and retention of salt within the estuary. 相似文献
15.
This research investigates the dynamics of the axial tidal flow and residual circulation at the lower Guadiana Estuary, south Portugal, a narrow mesotidal estuary with low freshwater inputs. Current data were collected near the deepest part of the channel for 21 months and across the channel during two (spring and neap) tidal cycles. Results indicate that at the deep channel, depth-averaged currents are stronger and longer during the ebb at spring and during the flood at neap, resulting in opposite water transport directions at a fortnightly time scale. The net water transport across the entire channel is up-estuary at spring and down-estuary at neap, i.e., opposite to the one at the deep channel. At spring tide, when the estuary is considered to be well mixed, the observed pattern of circulation (outflow in the deep channel, inflow over the shoals) results from the combination of the Stokes transport and compensating return flow, which varies laterally with the bathymetry. At neap tide (in particular for those of lowest amplitude each month), inflows at the deep channel are consistently associated with the development of gravitational circulation. Comparisons with previous studies suggest that the baroclinic pressure gradient (rather than internal tidal asymmetries) is the main driver of the residual water transport. Our observations also indicate that the flushing out of the water accumulated up-estuary (at spring) may also produce strong unidirectional barotropic outflow across the entire channel around neap tide. 相似文献
16.
The contribution of terrigenous organic matter (TOM) to high molecular weight dissolved and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. Dissolved organic matter (DOM) was fractionated by ultrafiltration into 1–30 kDa (HDOM) and 30 kDa–0.2 μm (VHDOM) nominal molecular weight fractions. Thermochemolysis with tetramethylammonium hydroxide (TMAH) was used to release and quantify lipids and lignin phenols. Stable carbon isotopes, fatty acids and lignin content indicated shifts in sources with terrigenous material in the river and turbid region and a predominantly algal/planktonic signal in the lower estuary and coastal ocean. Thermochemolysis with TMAH released significant amounts of short chain fatty acids (C9–C13), not seen by traditional alkaline hydrolysis, which appear to be associated with the macromolecular matrix. Lignin phenol distributions in HDOM, VHDOM and particles followed predicted sources with higher concentrations in the river and turbid region of the estuary and lower concentrations in the coastal ocean. TOM comprised 12% of HDOM within the coastal ocean and up to 73% of HDOM within the turbid region of the estuary. In the coastal ocean, TOM from high molecular weight DOM comprised 4% of total DOC. The annual flux of TOM from the Delaware Estuary to the coastal ocean was estimated at 2.0×1010 g OC year−1 and suggests that temperate estuaries such as Delaware Bay can be significant sources of TOM on a regional scale. 相似文献
17.
Dissolved inorganic nutrient elements were analyzed from the samples collected in the South Passage of the Changjiang (Yangtze River) Estuary in March 2003, including NH4 , NO3-, NO2- and PO43-. The water samples were collected with a Niskin sampler hourly at the near-surface, middle and near-bottom depths at the three stations -A1, A2 and A3-during two complete tidal cycles of neap tide and spring tide. Results showed that 1) the concentrations of NH4 , NO3- and NO2- were a little higher respectively during the neap tide than those during the spring tide, while PO43- showed an opposite trend, and each was higher in the ebb tide than in the flood tide, either for the neap tidal cycle or the spring tidal cycle; 2) higher stratification of the nutrients existed obviously in this area, with the concentrations of which increased from the bottom to the surface, especially for NH4 and NO3-; 3) the coefficient of variation (C.V.) values of all dissolved inorganic nutrients varied from 4.06% to 36.8% beyond different influences of the tidal current and Changjiang runoff; 4) with increasing suspended matter in the water column, the concentrations of PO43- became lower in the filtered water; and 5) the total transport of each tidal cycle was much more in the spring tide than in the neap tide, and the positive values indicated that the nutrients had been exported to the East China Sea. Studies on the variations and net transport of dissolved inorganic nutrients in the South Passage of the Changjiang Estuary will provide the scientific basis for the study of the mechanism of red tide in the East China Sea. 相似文献
18.
19.
珠江口的沉积作用和沉积相 总被引：6，自引：2，他引：6
珠江口为华南沿海的重要河口,是珠江水(系(西江、北江、东江、流溪河)的受水盆地。珠江流域每年有8000余万吨悬沙。大约3000万吨溶解质和少量底沙进入珠江河口区域,它们在迳流、潮流和其他海洋动力因素共同影响下,沉积作用甚为活跃。但是珠江口水域宽阔,地形复杂,各河口、河口湾或湾外区域的动力背景及泥沙运动不尽相同,因而其沉积作用和沉积特征也具有区域差异。 相似文献
20.
A rhodamine dye tracer study was conducted over eight tidal cycles to investigate mixing and tidal exchange processes in Perch Pond, a Cape Cod embayment subject to recurrent blooms of the toxic dinoflagellate, Gonyaulax tamarensis. Dye injected at the inlet to Perch Pond during flood tide became well-mixed within the pond in one day and was removed at an effective first order rate of 0.36 d?1, equivalent to a 70% utilization of the maximum possible tidal exchange. This relatively high flushing efficiency can be attributed to a density-driven circulation within the pond, consisting of a subsurface inflow of high salinity dense water on the flood tide followed by removal of lighter surface layers through the shallow inlet during ebb tide. The formation of a frontal convergence near the inlet on flood tide is consistent with the observed distribution of G. tamarensis cysts and shelifish toxicity. It is also clear that phytoplankton like G. tamarensis, whose maximum growth rates approximate the rate of tidal flushing, can only bloom within the embayment by avoiding the outflowing surface waters. Mixing within the pond is probably less efficient and population losses greater during dry periods when the pond salinity is higher and the stratification weaker. 相似文献