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1.
Rhythmic movements in response to tidal cycles are characteristic of infaunal inhabitant of intertidal soft-bottoms, allowing them to remain in the area with best living conditions. The effect of bioturbators as modifier of local environmental conditions and thus of gradients in intertidal habitats, has not been investigated yet. The Atlantic estuarine intertidal areas are dominated by the burrowing crabChasmagnathus granulatus that generates strong environmental heterogeneity by affecting the physical-chemical characteristics of the sediment. The comparison between intertidal areas with and without crab shows that sediments in the crab beds remain more humid, softer, and homogeneous across the intertidal and along the tidal cycle than areas without crabs. The densities of infauna were higher at high intertidal zones in crab beds than in similar areas without crabs. Infaunal organisms performed vertical movements into the sediment following the tidal cycle that were always of higher magnitude in habitats without crabs. Infaunal species tend to spend most of the time buried into the sediment in the crab bed. Migratory shorebirds use the Atlantic estuarine environments as stopover or wintering sites. They feed (mainly on polychaetes) in the low intertidal zones of both habitats (with and without crabs), but they also feed in the upper intertidal of the crab bed; polychaete per capita mortality rate is higher in the upper part of the crab bed. Environmental heterogeneity produced by crab disturbance has an effect on the infaunal behavior, risk of mortality, and the zonation pattern. This is another example of the ecosystem engineering ability of a burrowing intertidal species.  相似文献   

2.
Spatial patterns of environmental processes are intrinsic yet complex components of estuaries. Spatial characterization of environmental gradients is a necessary step to better understand and classify estuarine environments. A geographic information system is developed to analyze the major abiotic environmental processes, to evaluate accuracy and spatial uncertainty, and to analyze potential zonation within the choked coastal lagoon of Chincoteague Bay in Maryland and Virginia, USA. Spatially extensive grid-based models of environmental gradients are constructed from existing geospatial and environmental databases, including tidal prism, bathymetry, salinity, wave exposure, and Secchi disk depth. Integration of wetland boundaries and bathymetric data provide for full basin analysis of flushing and tidal prism. Multivariate Principal Components Analysis demonstrates the covariation among gradients and provides an empirical approach to mapping multidimensional zones within the lagoon. The project documents the development of an estuarine geographic information system that can be used to analyze and compare estuarine environments and provide data for environmental decision making.  相似文献   

3.
It is often presumed that salt marshes provide a predation refuge for small fishes, but predation risks have rarely been compared in intertidal and subtidal habitats, making the importance of salt marshes as a predation refuge speculative. We measured relative survival of tethered mummichog (Fundulus heteroclitus) in four habitats in a salt marsh?Ctidal creek system: unvegetated and vegetated intertidal areas and the subtidal creek at high and low tide. At high tide, mummichog in the intertidal zone had significantly higher survival than in the subtidal creek in June through August. Survival rates in unvegetated and vegetated intertidal habitats were not significantly different, suggesting that higher intertidal survival was due to less abundant predators compared with the creek, rather than predators being less effective in vegetation. The lower predation risk experienced by mummichog in the intertidal marsh suggests that access to intertidal habitats will be important for production of small estuarine fishes.  相似文献   

4.
Backwater tidal sloughs are commonly found at the landward boundary of estuaries. The Cache Slough complex is a backwater tidal region within the Upper Sacramento–San Joaquin Delta that includes two features that are relevant for resource managers: (1) relatively high abundance of the endangered fish, delta smelt (Hypomesus transpacificus), which prefers turbid water and (2) a recently flooded shallow island, Liberty Island, that is a prototype for habitat restoration. We characterized the turbidity around Liberty Island by measuring suspended-sediment flux at four locations from July 2008 through December 2010. An estuarine turbidity maximum in the backwater Cache Slough complex is created by tidal asymmetry, a limited tidal excursion, and wind-wave resuspension. During the study, there was a net export of sediment, though sediment accumulates within the region from landward tidal transport during the dry season. Sediment is continually resuspended by both wind waves and flood tide currents. The suspended-sediment mass oscillates within the region until winter freshwater flow pulses flush it seaward. The hydrodynamic characteristics within the backwater region such as low freshwater flow during the dry season, flood tide dominance, and a limited tidal excursion favor sediment retention.  相似文献   

5.
Tidal freshwater sections of the Cooper River Estuary (South Carolina) include extensive wetlands, which were formerly impounded for rice culture during the 1,700s and 1,800s. Most of these former rice fields are now open to tidal exchange and have developed into productive wetlands that vary in bottom topography, tidal hydrography and vegetation dominants. The purpose of this project was to quantify nitrogen (N) transport via tidal exchange between the main estuarine channel and representative wetland types and to relate exchange patterns to the succession of vegetation dominants. We examined N concentration and mass exchange at the main tidal inlets for the three representative wetland types (submerged aquatic vegetation [SAV], floating leaf vegetation, and intertidal emergent marsh) over 18-21 tidal cycles (July 1998–August 2000). Nitrate + nitrite concentrations were significantly lower during ebb flow at all study sites, suggesting potential patterns of uptake by all wetland types. The magnitude of nitrate decline during ebb flow was negatively correlated with oxygen concentration, reflecting the potential importance of denitrification and nitrate reduction within hypoxic wetland waters and sediments. The net tidal exchange of nitrate + nitrite was particularly consistent for the intertidal emergent marsh, where flow-weighted ebb concentrations were usually 18–40% lower than during flood tides. Seasonal patterns for the emergent marsh indicated higher rates of nitrate + nitrite uptake during the spring and summer (> 400 μmol N m-2 tide-1) with an annual mean uptake of 248 ± 162 μmol m–2 tide–1. The emergent marsh also removed ammonium through most of the year (207 ± 109 μmol m–2 tide–1), and exported dissolved organic nitrogen (DON) in the fall (1,690 ± 793 μmol m–2 tide–1), suggesting an approximate annual balance between the dissolved inorganic N uptake and DON export. The other wetland types (SAV and floating leaf vegetation) were less consistent in magnitude and direction of N exchange. Since the emergent marsh site had the highest bottom elevation and the highest relative cover of intertidal habitat, these results suggest that the nature of N exchange between the estuarine waters and bordering wetlands is affected by wetland morphometry, tidal hydrography, and corresponding vegetation dominants. With the recent diversion of river discharge, water levels in the upper Cooper estuary have dropped more than 10 cm, leading to a succession of wetland communities from subtidal habitats toward more intertidal habitats. Results of this study suggest that current trends of wetland succession in the upper Cooper River may result in higher rates of system-wide inorganic N removal and DON inputs by the growing distributions of intertidal emergent marshes.  相似文献   

6.
One of the most conspicuous anthropogenic disturbances to estuaries worldwide has been the alteration of freshwater and tidal influence through the construction of water control structures (dikes, tide gates, culverts). Few studies have rigorously compared the responses of differing groups of organisms that serve as contrasting conservation targets to such anthropogenic disturbances in estuarine ecosystems. Elkhorn Slough in central California includes a spectrum of tidally restricted habitats behind water control structures and habitats experiencing full tidal exchange. To assess community composition for several different taxa in habitats with varying tidal exchange, we employed a variety of field approaches and synthesized results from several different studies. Overall, we found that communities at sites with moderately restricted tidal exchange were fairly similar to those with full tidal exchange, but those with extremely restricted tidal exchange were markedly different from other categories. These differences in community composition are likely the result of several factors, including restricted movement due to physical barriers, differences in water quality characteristics, and differences in habitat structure. Indeed, in this study, we found that water quality characteristics strongly vary with tidal restriction and may strongly influence patterns of species presence or absence. We also found that different conservation targets showed contrasting responses to variation in tidal exchange. Full exchange appears to favor native oysters, commercially valuable flatfish, migratory shorebirds, and site-level biodiversity. Minimal tidal exchange due to water control structures supports a suite of estuarine endemics (including the tidewater goby and California brackish snail) not represented elsewhere and minimizes invasions by non-native marine species. Altogether, our results suggest that total estuary-wide biodiversity may be enhanced with a mosaic of tidal exchange regimes.  相似文献   

7.
In late December 1991, an accidental release of 5,700 CI of tritiated water (HTO) from the Savannah River Site was transported via site streams into the Savannah River where it was carried downstream to the coastal zone. HTO released into a semitropical Georgia estuary was forced into the tidal marshes surrounding the estuary as well as discharged directly into the Atlantic Ocean. The spreading of HTO was studied with a 3D hydrodynamic model (ALGE) that includes flooding and draining of intertidal areas. Comparisons of model simulations to measured HTO concentration showed that ALGE simulated well the general increase and decrease of HTO as its plume passed a given area. The “sheet flow” approximation for marsh and small tidal creek flow largely compensated for lack of model resolution and accurate bathymetry in areas with numerous small to medium-sized tidal creeks. The water volume of the unresolved tidal creeks had to be accounted for in the simulations by increasing the initial water depth over the marshes. ALGE and a simple box model both reproduced the trapping of HTO in intertidal areas. The time scale over which intertidal areas import and export HTO back to the tidal channels varies between 10 and 30 days.  相似文献   

8.
A high-resolution coastal ocean model is used to investigate salinity variability and water exchange in a complex coastal system off the southern U.S. characterized by three adjacent sounds that are interconnected by a network of channels, creeks, and intertidal areas. Model results are generally highly correlated with observations from the Georgia Coastal Ecosystem Long Term Ecological Research (GCE-LTER) program, revealing a high degree of salinity variability at the Altamaha River and Doboy Sound, decreasing sharply toward Sapelo Sound. A Lagrangian particle tracking method is used to investigate local residence time and connectivity in the system. Local residence time is highly variable, increasing with distance from the Altamaha River and decreasing with river flow, revealing that discharge plays a dominant role on transport processes and estuary-shelf exchange. The Altamaha River and Doboy Sound are connected to each other in all seasons, with exchange occurring both via coastal and estuarine pathways. While particles released at the Altamaha and Doboy rarely reach Sapelo Sound, particles released at Sapelo Sound and the creeks surrounding its main channel can reach the entire estuarine system.  相似文献   

9.
Deepening of estuarine channels is a common practice to ensure navigation. Here, we investigate whether such deepening impacts physical processes such as the strength of the estuarine exchange flow, the horizontal salinity gradient, and tidal dynamics. We analyze recent and historical hydrodynamic observations in Newark Bay, New Jersey, to assess the effect of channel deepening on tides, circulation, and salinity. The Bay’s navigational channel has undergone significant deepening, from 3 to 10 m in the nineteenth century to ~16 m today. Observations presented here include sea-level data from the nineteenth, twentieth, and twenty-first century, and moored Doppler current data and bottom salinity measurements made over the past 20 years. Results show a doubling of the estuarine exchange flow, a slight increase in salinity and in the horizontal salinity gradient, a decrease in tidal current amplitude, and a spatially variable change in the tidal range. The doubling of the exchange flow is consistent with the Hansen and Rattray scaling provided that the horizontal salinity gradient is unable to fully adjust landward because the dredging is limited to a short reach of the estuary. However, uncertainty in channel depth leaves open the possibility that the exchange flow is also augmented by an increase in the horizontal salinity gradient and/or a reduction in vertical mixing. Nevertheless, results demonstrate that a relatively small (15%) increase in depth appears to have doubled the exchange flow. We believe that this result is relevant to other systems where dredging is limited to a short reach of an estuary.  相似文献   

10.
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11.
极浅水边界层的沉积环境效应   总被引：1，自引：1，他引：0  
高抒 《沉积学报》2010,28(5):926-932
极浅水环境是水深远小于正常边界层厚度的环境,潮滩滩面和潮水沟就经常处于这种环境之中。来自江苏潮滩的观察资料表明,落潮后期滩面和潮水沟在薄层低速水流作用下可形成浅水波痕、平床和次级潮水沟形态,而边界层内的流速结构仍然得以维持,物质输运强度也与Von Kármán-Prandtl模型所定义的u100数值相一致。涨急时段中潮位附近形成的滩面涌潮是极浅水边界层的另一种动力学行为,它代表薄层高速水流作用下发生的底部边界层系统的崩溃,此时Von Kármán-Prandtl模型所刻画的流速结构不复存在。滩面涌潮高度是系统崩溃的临界水深,它可以定量地表示为Hb=4z0。极浅水边界层过程对潮滩沉积和地貌形成具有独特的作用。  相似文献   

12.
Cool-water skeletal carbonate sediments are forming in Spencer Gulf, South Australia, an area of high salinity and moderate tidal range. Four environments can be distinguished: deeper marine areas (10–20 m); shallow subtidal platforms and banks (2–10 m); intertidal and supratidal zones; and coastal springs and lakes fed by saline continental groundwaters. The sediments are predominately bioclastic carbonate sands; muddy sediments occur in protected intertidal environments. The most common grain types are gastropods, bivalves, foraminifera, coralline algae and quartz. Indurated non-skeletal carbonate grains have not been seen. Composition of the sediment varies little between environments, but considerable textural variation results from variation in the stability of the substrate, hydrodynamic conditions, depth of water, period of tidal inundation, supply of terrigenous grains, temperature, and salinity. The Spencer Gulf data suggests that temperature, and particularly minimum temperature, controls the distribution of skeletal and non-skeletal grain associations in high-salinity environments. The textures of the sedimentary facies of Spencer Gulf closely parallel those of equivalent environments in warm-water carbonate provinces.  相似文献   

13.
The fringing environments of lower Chesapeake Bay include sandy shoals, seagrass meadows, intertidal mud flats, and marshes. A characterization of a fringing ecosystem was conducted to provide initialization and calibration data for the development of a simulation model. The model simulates primary production and material exchange in the littoral zone of lower Chesapeake Bay. Carbon (C) and nitrogen (N) properties of water and sediments from sand, seagrass, intertidal silt-mud, and intertidal marsh habitats of the Goodwin Islands (located within the Chesapeake Bay National Estuarine Research Reserve in Virginia, CBNERR-VA) were determined seasonally. Spatial and temporal differences in sediment microalgal biomass among the habitats were assessed along with annual variations in the distribution and abundance ofZostera marina L. andSpartina alterniflora Loisel. Phytoplankton biomass displayed some seasonality related to riverine discharge, but sediment microalgal biomass did not vary spatially or seasonally. Macrophytes in both subtidal and intertidal habitats exhibited seasonal biomass patterns that were consistent with other Atlantic estuarine ecosystems. Marsh sediment organic carbon and inorganic nitrogen differed significantly from that of the sand, seagrass, and silt habitats. The only biogeochemical variable that exhibited seasonality was low marsh NH4 +. The subtidal sediments were consistent temporally in their carbon and nitrogen content despite seasonal changes in seagrass abundance. Eelgrass has a comparatively low C:N ratio and is a potential N sink for the ecosystem. Changes in the composition or size of the vegetated habitats could have a dramatic influence over resource partitioning within the ecosystem. A spatial database (or geographic information system, GIS) of the Goodwin Islands site has been initiated to track long-term spatial habitat features and integrate model output and field data. This ecosystem characterization was conducted as part of efforts to link field data, geographic information, and the dynamic simulation of multiple habitats. The goal of these efforts is to examine ecological structure, function, and change in fringing environments of lower Chesapeake Bay.  相似文献   

14.
Short-term otolith growth rates, residence times, and forage of two species of juvenile salmon (Oncorhynchus spp.) were compared in a created and natural estuarine slough on the Chehalis River in Washington to assess the functional equivalency of the created slough in providing suitable rearing habitat. Otolith microstructure, mark-recapture data, and forage of sub-yearling chinook, O. tshawytscha, and coho, O. kisutch, residing in both sloughs during the spring of 1991 and 1992 served as indicators of rearing habitat quality. No significant differences in the number or width of coho daily otolith increments were detected between the sloughs. Juvenile chinook residence and emigration times were also comparable. Aquatic and terrestrial insects composed the majority of all chinook and coho diets; however, the order of importance of main prey items did differ between sloughs, and salmon in the created slough had emptier stomachs, possibly because of reduced prey availability and/or foraging efficiency.  相似文献   

15.
Detritus from terrestrial ecosystems is the major source of organic matter in many streams, rivers, and estuaries, yet the role of detritus in supporting pelagic food webs is debated. We examined the importance of detritus to secondary productivity in the Sacramento and San Joaquin River Delta (California, United States), a large complex of tidal freshwater habitats. The Delta ecosystem has low primary productivity but large detrital inputs, so we hypothesized that de tritus is the primary energy source fueling production in pelagic food webs. We assessed the sources, quantity, composition, and bioavailability of organic matter among a diversity of habitats (e.g., marsh sloughs, floodplains, tidal lakes, and deep river channels) over two years to test this hypothesis. Our results support the emerging principle that detritus dominates riverine and estuarine organic matter supply and supports the majority of ecosystem metabolism. Yet in contrast to prevailing ideas, we found that detritus was weakly coupled to the Delta's pelagic food web. Results from independent approaches showed that phytoplankton production was the dominant source of organic matter for the Delta's pelagic food web, even though primary production accounts for a small fraction of the Delta's organic matter supply. If these results are general, they suggest that the value of organic matter to higher trophic levels, including species targeted by programs of ecosystem restoration, is a function of phytoplankton production.  相似文献   

16.
A buried archaeological site at Tecolote Canyon provides an ideal case study for relating past human land use patterns to changes in coastal paleogeography. Postglacial sea level transgression, erosion, and other marine and fluvial processes form the context for examining two deeply buried archaeological components excavated at CA‐SBA‐72. Archaeological shellfish assemblages provide proxy data for evaluating the evolution of local marine environments. Pismo clams dominate shellfish assemblages dated to 5800 cal yr B.P., suggesting the presence of a broad and sandy, high‐energy beach environment. At 5500 cal yr B.P., the almost exclusive use of California mussels by humans signals the development of rocky intertidal habitats. During the late Holocene, estuarine species dominate the marine mollusk assemblages at CA‐SBA‐72, reflecting the development of local estuarine conditions or trade with nearby Goleta Slough villages. The buried components at Tecolote Canyon appear to have served as temporary camps for shellfish harvesting and processing. While general changes in coastal paleogeography and human subsistence have been reconstructed for the Santa Barbara Coast, high resolution ecological data from Tecolote Canyon suggest that Native peoples also adapted to localized and shorter‐term shifts in intertidal habitats, changes not evident in most larger or more disturbed surface sites in the region. Linking these changes with shifts in human land use patterns highlights the interaction between humans and a dynamic coastal system. These data demonstrate the importance of small, buried sites in understanding the full spectrum of human subsistence and settlement choices and local environmental change. © 2004 Wiley Periodicals, Inc.  相似文献   

17.
To assess the effects of tidal energy extraction on water quality in a simplified estuarine system, which consists of a tidal bay connected to the coastal ocean through a narrow channel where energy is extracted using in-stream tidal turbines, a three-dimensional coastal ocean model with built-in tidal turbine and water quality modules was applied. The effects of tidal energy extraction on water quality were examined for two energy extraction scenarios as compared with the baseline condition. It was found, in general, that the environmental impacts associated with energy extraction depend highly on the amount of power extracted from the system. Model results indicate that, as a result of energy extraction from the channel, the competition between decreased flushing rates in the bay and increased vertical mixing in the channel directly affects water quality responses in the bay. The decreased flushing rates tend to cause a stronger but negative impact on water quality. On the other hand, the increased vertical mixing could lead to higher bottom dissolved oxygen at times. As the first modeling effort directly aimed at examining the impacts of tidal energy extraction on estuarine water quality, this study demonstrates that numerical models can serve as a very useful tool for this purpose. However, more careful efforts are warranted to address system-specific environmental issues in real-world, complex estuarine systems.  相似文献   

18.
This study was designed to investigate seasonal changes on food available for benthic consumers in relation to tidal levels and sediment depth in an estuarine beach. The relationships between the biochemical characteristics of sedimentary organic matter and benthic macrofauna were analyzed quarterly over 2 years (from January 1997 to January 1999), in an estuarine soft intertidal zone from the NW coast of Spain (42°64′04″N, 8°88′36″W). Sediment samples were collected to provide a two-dimensional view of macroinfauna distribution in the intertidal zone and its relationship with the quantity and quality of the organic matter. The nutritional value of organic matter (i.e., lipid, protein, and carbohydrate) and the content of chlorophyll a of the sediment were measured. Macrofaunal assemblages and food availability in the sediment were studied at three tidal levels on the shore: two intertidal and one supratidal. Macroinfauna and biochemical compounds showed a clear vertical stratification with the highest macrofaunal abundance at the superficial layer of the sediment, where redox potential discontinuity was also observed. Crustaceans were found mainly inhabiting the supratidal level of the estuarine beach, while polychaetes and mollusks occupied the intertidal level. Food availability, measured as biopolymeric carbon, and also chlorophyll a from the sediment were better related to macroinfauna abundance, biomass, and abundance of main taxonomic groups. Macrofauna assemblages showed particular distribution in both vertical and horizontal ranges suggesting specific preferences to several abiotic factors. No clear seasonal pattern was found in macrofauna and sedimentary organic characteristics suggesting that macrofaunal assemblages are controlled by complex and unpredictable factors, including small-scale changes in substrate and hydrological characteristics.  相似文献   

19.
Intertidal (tidal flat) reclamation along the Chinese coastline, especially which is in Jiangsu Province, has increased markedly in recent years. However, the hydrodynamic disturbance and environmental impacts of this activity are not yet fully understood. In this study, a process-based depth-averaged model is used to evaluate quantitatively the possible impacts of intertidal reclamation for the southern Yellow Sea region. The simulation results show that reclamation of both inshore and offshore intertidal areas of ~1800 km2 (according to the approved governmental reclamation scheme) would result in three remarkable changes in tidal patterns: enhanced M2 and M4 tidal amplitudes in coastal areas, strengthened negative tidal asymmetry in the southern region of the sand ridge system, and an enhanced tidal energy flux toward offshore through the main channels in the south. These changes would result in some negative impacts. The enhancement in local tidal amplitude could increase the probability of coastal hazards, and the offshore sediment transport tendency resulting from negative tidal asymmetry in the south could lead to severe erosion. The enhanced energy flux transported offshore may also affect far-field regions. On the other hand, alternative reclamation of ~400 km2 of offshore intertidal area could significantly minimize hydrodynamic disturbances to the local tidal system. Offshore reclamation with lower environment impacts may be the future for coastal development. To cope with the potential environmental risks caused by reclamation, it is recommended to strengthen environmental impact assessment and overseeing of reclamation plans, and advance international cooperation in terms of coastal management. Our findings provide a reference for coastal management in countries with substantial areas of tidal flats.  相似文献   

20.
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   

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