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1.
The coastal zone of the Great Barrier Reef shelf, with an area of 30,000 km(2) and a water volume of 300 km(3), receives an average annual input of sediment on the order of 14-28 Mty(-1)--an estimated two- to fourfold increase since European settlement. There is considerable concern about the impact and ultimate fate of terrestrially-derived nutrients entering the Great Barrier Reef World Heritage Area (GBRWHA). Analysis of current data suggests that microbial communities in coastal waters and in unconsolidated sediments metabolise nutrients equivalent to the entire dissolved and particulate nutrient load debouched from land. River-derived nutrients account for 40-80% of the carbon, 13-30% of the nitrogen, and 2-5% of the phosphorus necessary to support the observed rates of benthic and pelagic mineralisation in Princess Charlotte Bay in the far north, and in Rockingham Bay and Missionary Bay in the central section, of the GBRWHA. Nearly all nitrogen is ultimately returned to the atmosphere via denitrification. There is little net burial of nutrients in subtidal sediments. These budget estimates are based on a sparse data set, but it is clear that marine sources of nutrients (N-fixation by pelagic and benthic cyanobacteria) must be important, but the magnitude of these sources is poorly known and likely to be highly variable in space and time. Data from sediment trap deployments suggest that, despite significant re-suspension, sedimentation fluxes are sufficient to balance benthic mineralisation rates. Most organic material deposited to the benthos appears to be flocculent or colloidal aggregates, perhaps formed via microbial mediation and exudation of extra-cellular material. The geophysical dynamics of the coastal boundary layer plays an important role in concentrating biological and biogeochemical activity within a shallow, narrow coastal zone. Mangroves and tidal flats are small in area, but trap, transform, and store a disproportionate amount of sediment and organic matter within the GBRWHA. The highly efficient use of terrestrially-derived nutrients by benthic and pelagic microbes in the coastal zone helps to explain why coral reefs on the middle and outer shelf have remained relatively unscathed despite a significant increase in sediment delivery.  相似文献   

2.
Sea breezes often have significant impacts on nearshore physical and biological processes. We document the effects of a diurnal sea breeze on the nearshore thermal structure and circulation of northern Monterey Bay, California, using an array of moorings during the summer upwelling season in 2006. Moorings were equipped with thermistors and Acoustic Doppler Current Profilers (ADCPs) to measure temperature and currents along the inner shelf in the bay. Temperature and current data were characteristic of traditional regional scale upwelling conditions along the central California coast during the study period. However, large diurnal fluctuations in temperature (up to 5 °C) were observed at all moorings inshore of the 60-m isobath. Examination of tidal, current, temperature, and wind records revealed that the observed temperature fluctuations were the result of local diurnal upwelling, and not a result of nearshore mixing events. Westerly diurnal sea breezes led to offshore Ekman transport of surface waters. Resulting currents in the upper mixed layer were up to 0.10 m s−1 directed offshore during the afternoon upwelling period. Surface water temperatures rapidly decreased in response to offshore advection of surface waters and upwelling of cold, subsurface water, despite occurring in the mid-afternoon during the period of highest solar heat flux. Surface waters then warmed again during the night and early morning as winds relaxed and the upwelling shadow moved back to shore due to an unbalanced onshore pressure gradient. Examination of season-long, moored time series showed that local diurnal upwelling is a common, persistent feature in this location. Local diurnal upwelling may supply nutrients to nearshore kelp beds, and transport larvae to nearshore habitats.  相似文献   

3.
Acoustic Doppler current profiles and current meter data are combined with wind observations to describe the transport of water leaving Florida Bay and moving onto the inner shelf on the Atlantic side of the Florida Keys. A 275-day study in the Long Key Channel reveals strong tidal exchanges, but the average ebb tide volume leaving Florida Bay is 19% greater than the average flood tide volume entering the bay. The long-term net outflow averages 472 m3 s−1. Two studies in shelf waters describe the response to wind forcing during spring and summer months in 2004 and during fall and winter months in 2004–2005. During the spring–summer study, southeasterly winds have a distinct shoreward component, and a two-layer pattern appears. Surface layers move shoreward while near-bottom layers move seaward. During the winter study, the resultant wind direction is parallel to the Keys and to the local isobaths. The entire water column moves in a nearly downwind direction, and across-shelf transport is relatively small. During the summer wet season, Florida Bay water should be warmer, fresher, and thus less dense than Atlantic shelf waters. Ebbing bay water should move onto the shelf as a buoyant plume and be held close to the Keys by southeasterly winds. During the winter dry season, colder and saltier Florida Bay water should leave the tidal channels with relatively high density and be concentrated in the near-bottom layers. But little across-shelf flow occurs with northeasterly winds. The study suggests that seasonally changing wind forcing and hydrographic conditions serve to insulate the reef tract from the impact of low-quality bay water.  相似文献   

4.
Massachusetts Bay is a semi-enclosed embayment in the western Gulf of Maine about 50 km wide and 100 km long. Bottom sediment resuspension is controlled predominately by storm-induced surface waves and transport by the tidal- and wind-driven circulation. Because the Bay is open to the northeast, winds from the northeast (‘Northeasters’) generate the largest surface waves and are thus the most effective in resuspending sediments. The three-dimensional oceanographic circulation model Regional Ocean Modeling System (ROMS) is used to explore the resuspension, transport, and deposition of sediment caused by Northeasters. The model transports multiple sediment classes and tracks the evolution of a multilevel sediment bed. The surficial sediment characteristics of the bed are coupled to one of several bottom-boundary layer modules that calculate enhanced bottom roughness due to wave–current interaction. The wave field is calculated from the model Simulating WAves Nearshore (SWAN). Two idealized simulations were carried out to explore the effects of Northeasters on the transport and fate of sediments. In one simulation, an initially spatially uniform bed of mixed sediments exposed to a series of Northeasters evolved to a pattern similar to the existing surficial sediment distribution. A second set of simulations explored sediment-transport pathways caused by storms with winds from the northeast quadrant by simulating release of sediment at selected locations. Storms with winds from the north cause transport southward along the western shore of Massachusetts Bay, while storms with winds from the east and southeast drive northerly nearshore flow. The simulations show that Northeasters can effectively transport sediments from Boston Harbor and the area offshore of the harbor to the southeast into Cape Cod Bay and offshore into Stellwagen Basin. This transport pattern is consistent with Boston Harbor as the source of silver found in the surficial sediments of Cape Cod Bay and Stellwagen Basin.  相似文献   

5.
Nutrient and suspended sediment concentrations were measured in the dry season and during the rising and falling stages of flood events in the Annan and Daintree rivers to estimate catchment exports. These flood events were also sampled along the salinity gradient in the estuary and nearshore shelf to quantify the modification of terrestrial sediment and nutrient loads as they pass through estuaries into the Great Barrier Reef lagoon. In the Daintree River TSS concentrations were found to increase between the catchment and the estuary plume. The source of TSS may have been scour of the estuarine channel or from land use in the catchment of the lower estuary. In the dry season nitrogen enters the Annan and Daintree estuaries predominantly in the form of PON and DON in roughly equal proportions. Nitrogen exports to the GBR are mostly in the form of DON. In the wet season the majority of nitrogen enters the estuaries as DON and leaves as PON. Nitrogen removal in the estuaries and plumes appears to be biologically mediated once suspended sediment concentrations decrease to a point where phytoplankton growth is not light limited. In the dry season phosphorus enters and leaves the estuaries primarily in organic form. PIP is the dominant form of phosphorus in river water, but leaves the estuary more evenly distributed between all forms. These estuarine processes result in less nitrogen and phosphorus being delivered to the GBR lagoon than is exported from the catchment. The differences between these estuaries highlights the need for further work to explore modifications in estuaries that drain into the Great Barrier Reef lagoon.  相似文献   

6.
Marine plants colonise several interconnected ecosystems in the Great Barrier Reef region including tidal wetlands, seagrass meadows and coral reefs. Water quality in some coastal areas is declining from human activities. Losses of mangrove and other tidal wetland communities are mostly the result of reclamation for coastal development of estuaries, e.g. for residential use, port infrastructure or marina development, and result in river bank destabilisation, deterioration of water clarity and loss of key coastal marine habitat. Coastal seagrass meadows are characterized by small ephemeral species. They are disturbed by increased turbidity after extreme flood events, but generally recover. There is no evidence of an overall seagrass decline or expansion. High nutrient and substrate availability and low grazing pressure on nearshore reefs have lead to changed benthic communities with high macroalgal abundance. Conservation and management of GBR macrophytes and their ecosystems is hampered by scarce ecological knowledge across macrophyte community types.  相似文献   

7.
For the managers of a region as large as the Great Barrier Reef, it is a challenge to develop a cost effective monitoring program, with appropriate temporal and spatial resolution to detect changes in water quality. The current study compares water quality data (phytoplankton abundance and water clarity) from remote sensing with field sampling (continuous underway profiles of water quality and fixed site sampling) at different spatial scales in the Great Barrier Reef north of Mackay (20 degrees S). Five transects (20-30 km long) were conducted from clean oceanic water to the turbid waters adjacent to the mainland. The different data sources demonstrated high correlations when compared on a similar spatial scale (18 fixed sites). However, each data source also contributed unique information that could not be obtained by the other techniques. A combination of remote sensing, underway sampling and fixed stations will deliver the best spatial and temporal monitoring of water quality in the Great Barrier Reef.  相似文献   

8.
Ocean circulation influences nearly all aspects of the marine ecosystem. This study describes the water circulation patterns on time scales from hours to years across Torres Strait and adjacent gulfs and seas, including the north of the Great Barrier Reef. The tridimensional circulation model incorporated realistic atmospheric and oceanographic forcing, including winds, waves, tides, and large-scale regional circulation taken from global model outputs. Simulations covered a hindcast period of 8 years (i.e. 01/03/1997–31/12/2004), allowing the tidal, seasonal, and interannual flow characteristics to be investigated. Results indicated that the most energetic current patterns in Torres Strait were strongly dominated by the barotropic tide and its spring-neap cycle. However, longer-term flow through the strait was mainly controlled by prevailing winds. A dominant westward drift developed in summer over the southeasterly trade winds season, which then weakened and reversed in winter over the northwesterly monsoon winds season. The seasonal flow through Torres Strait was strongly connected to the circulation in the north of the Great Barrier Reef, but showed little connectivity with the coastal circulation in the Gulf of Papua. Interannual variability in Torres Strait was highest during the monsoon period, reflecting variability in wind forcing including the timing of the monsoon. The characteristics of the circulation were also discussed in relation to fine sediment transport. Turbidity level in Torres Strait is expected to peak at the end of the monsoon, while it is likely to be at a low at the end of the trade season, eventually leading to a critically low bottom light level which constitutes a severe risk of seagrass dieback.  相似文献   

9.
《Continental Shelf Research》2006,26(17-18):2019-2028
Measurements of turbulence and suspended particulate matter (SPM) were measured over a 50 h period at a site in high tidal energy, mixed waters of the Irish Sea, NW European shelf. Turbulence parameters included both production (variance method from seabed ADCP) and dissipation (FLY profiler); SPM parameters included mass and volume concentrations and particle size (LISST 100 C). It is shown that the resultant SPM time series was due to a combination of time-varying turbulence at the measurement site and space-varying turbulence advecting through the site. Time asymmetry in turbulence at the site produced an asymmetric M4 signal in SPM volume concentration due to resuspension and disaggregation of flocs at times of peak turbulent energy. In terms of mass, the disaggregation contribution was 43% as much as the resuspension contribution near the bed, and 20% as much integrated throughout the water column. There was aggregation of flocs at high and low slack waters but the largest flocs occurred at low slack waters. Space-varying ambient turbulence was responsible for a horizontal gradient in floc size with small and large flocs at the high and low ends of the gradient, respectively; this generated a M2 signal in SPM properties. SPM concentrations and properties at any time resulted from combination of M2 and M4 variations which are responsible for the well-known twin peaks signature seen in transmissometer time series in tidal waters.  相似文献   

10.
A 2D depth-averaged numerical model is set up to simulate the macro-scale hydrodynamic characteristics, sediment transport patterns and morphological evolution in Hangzhou Bay, a large macro-tidal estuary on the eastern coast of China. By incorporating the shallow water equations, the suspended sediment transport equation and the mass-balance equation for sediment; short-term hydrodynamics, sediment transport and long-term morphological evolution for Hangzhou Bay are simulated and the underlying physical mechanisms are analyzed. The model reproduces the spatial distribution patterns of suspended sediment concentration (SSC) in Hangzhou Bay, characterized by three high SSC zones and two low SSC zones. It also correctly simulates the residual flow, the residual sediment transport and the sediment accumulation patterns in Hangzhou Bay. The model results are in agreement with previous studies based on field measurements. The residual flow and the residual sediment transport are landwards directed in the northern part of the bay and seawards directed in the southern part. Sediment accumulation takes place in most areas of the bay. Harmonic analysis revealed that the tide is flood-dominant in the northern part of the bay and ebb-dominant in the southern part of the bay. The strength of the flood-dominance increases landwards along the northern Hangzhou Bay. In turn sediment transport in Hangzhou Bay is controlled by this tidal asymmetry pattern. In addition, the direction of tidal propagation in the East China Sea, the presence of the archipelago in the southeast and the funnel-shaped geometry of the bay, play important roles for the patterns of sediment transport and sediment accumulation respectively.  相似文献   

11.
In the summer of 2001, a coastal ocean measurement program in the southeastern portion of San Pedro Bay, CA, was designed and carried out. One aim of the program was to determine the strength and effectiveness of local cross-shelf transport processes. A particular objective was to assess the ability of semidiurnal internal tidal currents to move suspended material a net distance across the shelf. Hence, a dense array of moorings was deployed across the shelf to monitor the transport patterns associated with fluctuations in currents, temperature and salinity. An associated hydrographic program periodically monitored synoptic changes in the spatial patterns of temperature, salinity, nutrients and bacteria. This set of measurements show that a series of energetic internal tides can, but do not always, transport subthermocline water, dissolved and suspended material from the middle of the shelf into the surfzone. Effective cross-shelf transport occurs only when (1) internal tides at the shelf break are strong and (2) subtidal currents flow strongly downcoast. The subtidal downcoast flow causes isotherms to tilt upward toward the coast, which allows energetic, nonlinear internal tidal currents to carry subthermocline waters into the surfzone. During these events, which may last for several days, the transported water remains in the surfzone until the internal tidal current pulses and/or the downcoast subtidal currents disappear. This nonlinear internal tide cross-shelf transport process was capable of carrying water and the associated suspended or dissolved material from the mid-shelf into the surfzone, but there were no observation of transport from the shelf break into the surfzone. Dissolved nutrients and suspended particulates (such as phytoplankton) transported from the mid-shelf into the nearshore region by nonlinear internal tides may contribute to nearshore algal blooms, including harmful algal blooms that occur off local beaches.  相似文献   

12.
This investigation showed that urban stormwater runoff provides a significant amount of petrogenic material to receiving waters and sediments. A characteristic hydrocarbon ‘fingerprint’ for sediments and particulate matter in the Hillsborough Reservoir, Hillsborough River and upper Hillsborough Bay was provided. Determination of source material for petroleum contamination in stormwater runoff and river sediment indicated that crankcase oil was a primary contributor to sediment hydrocarbon contamination. A comparison of sediment hydrocarbons with hydrocarbons from stormwater runoff showed that the most probable source of crankcase oil-like petrochemicals found in sediment was the stormwater runoff.A comparison of hydrocarbon composition in suspended particulate matter with that of accumulated bottom sediments in the reservoir, river and bay, during a non-storm period and rising tide showed no resuspension and upriver transport of petroleum contaminated bay sediment. No special influence of the bay upon the lower river was observed relative to hydrocarbon tracers, indicating that most contaminated sediment transport was downriver during storm events. Additional studies should be performed over various tidal cycles and storm events incorporating sediment cores, sediment grain size analysis and hydrocarbon characterization at more closely spaced stations near the river mouth to address adequately the question of specific hydrocarbon pollution sources, rate of petroleum influx and persistence of petrochemical contaminants in the sediment.  相似文献   

13.
A three-dimensional coupled hydrodynamic-sediment transport model for the Texas-Louisiana continental shelf was developed using the Regional Ocean Modeling System (ROMS) and used to represent fluvial sediment transport and deposition for the year 1993. The model included water and sediment discharge from the Mississippi River and Atchafalaya Bay, seabed resuspension, and suspended transport by currents. Input wave properties were provided by the Simulating WAves Nearshore (SWAN) model so that ROMS could estimate wave-driven bed stresses, critical to shallow-water sediment suspension. The model used temporally variable but spatially uniform winds, spatially variable seabed grain size distributions, and six sediment tracers from rivers and seabed.At the end of the year 1993, much of the modeled fluvial sediment accumulation was localized with deposition focused near sediment sources. Mississippi sediment remained within 20-40 km of the Mississippi Delta. Most Atchafalaya sediment remained landward of the 10-m isobath in the inner-most shelf south of Atchafalaya Bay. Atchafalaya sediment displayed an elongated westward dispersal pattern toward the Chenier Plain, reflecting the importance of wave resuspension and perennially westward depth-averaged currents in the shallow waters (<10 m). Due to relatively high settling velocities assumed for sediment from the Mississippi River as well as the shallowness of the shelf south of Atchafalaya Bay, most sediment traveled only a short distance before initial deposition. Little fluvial sediment could be transported into the vicinity of the “Dead Zone” (low-oxygen area) within a seasonal-annual timeframe. Near the Mississippi Delta and Atchafalaya Bay, alongshore sediment-transport fluxes always exceeded cross-shore fluxes. Estimated cumulative sediment fluxes next to Atchafalaya Bay were episodic and “stepwise-like” compared to the relatively gradual transport around the Mississippi Delta. During a large storm in March 1993, strong winds helped vertically mix the water column over the entire shelf (up to 100-m isobath), and wave shear stress dominated total bed stress. During fair-weather conditions in May 1993, however, the freshwater plumes spread onto a stratified water column, and combined wave-current shear stress only exceeded the threshold for suspending sediment in the inner-most part of the shelf.  相似文献   

14.
Surface waters of the inner shelf (coast to 20-m isobath) of the South Atlantic Bight (SAB) were sampled in July 1994 and August 1995 for pesticides currently used in the south-eastern United States to estimate offshore transport. Only atrazine was detected at all stations in 1994 and 1995 and simazine was detected at all stations in 1995. Atrazine levels were 5.60–12 ng/l in July 1994 and 3.1–11 ng/l in August 1995 and simazine levels were 0.8–4.6 ng/l in August 1995. We calculated reservoir masses (in inner shelf waters) of 550 kg atrazine in July 1994, and 325 kg atrazine and 180 kg simazine in August 1995. Using these reservoir masses and a previously estimated residence time for waters of the inner shelf of 30 days, annual export budgets were calculated. For 1994, a budget of 6600 kg atrazine was calculated. For 1995, budgets of 3900 kg atrazine and 2150 kg simazine were calculated.

Yearly riverine discharge to estuaries in the study region was estimated to range from 600 to 5600 kg atrazine and 100 to 550 kg simazine. The large budgets for the coastal inner shelf compared with yearly riverine discharge suggest that a significant fraction of atrazine and simazine applied in the region is being transported offshore from coastal waters. This transport pathway needs to be factored in when calculating mass balances and determining the ultimate fate of these pesticides.  相似文献   


15.
The characteristics of chromophoric dissolved organic matter (CDOM) were studied in Hudson Bay and Hudson Strait in the Canadian Arctic. Hudson Bay receives a disproportionately large influx of river runoff. With high dissolved organic matter (DOM) concentrations in Arctic rivers the influence of CDOM on coastal and ocean systems can be significant, yet the distribution, characteristics and potential consequences of CDOM in these waters remain unknown. We collected 470 discrete water samples in offshore, coastal, estuarine and river waters in the region during September and October 2005. Mixing of CDOM appeared conservative with salinity, although regional differences exist due to variable DOM composition in the rivers discharging to the Bay and the presence of sea-ice melt, which has low CDOM concentrations and low salinity. There were higher concentrations of CDOM in Hudson Bay, especially in coastal waters with salinities <28<28, due to river runoff. Using CDOM composition of water masses as a tracer for the freshwater components revealed that river runoff is largely constrained to nearshore waters in Hudson Bay, while sea-ice melt is distributed more evenly in the Bay. Strong inshore–offshore gradients in the bio-optical properties of the surface waters in the Hudson Bay cause large variation in penetration of ultraviolet radiation and the photic depth within the bay, potentially controlling the vertical distribution of biomass and occurrence of deep chlorophyll maxima which are prevalent only in the more transparent offshore waters of the bay. The CDOM distribution and associated photoprocesses may influence the thermodynamics and stratification of the coastal waters, through trapping of radiant heating within the top few meters of the water column. Photoproduction of biologically labile substrates from CDOM could potentially stimulate the growth of biomass in Hudson Bay coastal waters. Further studies are needed to investigate the importance of terrestrial DOM in the Hudson Bay region, and the impact of hydroelectric development and climate change on these processes.  相似文献   

16.
It has recently been shown that inner shelf waters of NE Monterey Bay, California function as an “extreme bloom incubator”, frequently developing dense “red tide” blooms that can rapidly spread. Located within the California Current upwelling system, this open bay is strongly influenced by oceanographic dynamics resulting from cycles of upwelling favorable winds and their relaxation and/or reversal. Different wind forcing causes influx of different water types that originate outside the bay: cold nutrient-rich waters during upwelling and warm nutrient-poor waters during relaxation. In this study, we examine how the bay's bloom incubation area can interact with highly variable circulation to cause red tide spreading, dispersal and retention. This examination of processes is supported by satellite, airborne and in situ observations of a major dinoflagellate bloom during August and September of 2004. Remote sensing of high spatial, temporal and spectral resolution shows that the bloom originated in the NE bay, where it was highly concentrated in a narrow band along a thermal front. Upwelling circulation rapidly spread part of the bloom, mixing cool waters of an upwelling filament with warm bloom source waters as they spread. Vertical migration of the dinoflagellate populations was mapped by autonomous underwater vehicle surveys through the spreading bloom. Following bloom expansion, a two-day wind reversal forced intrusion of warm offshore waters that dispersed much of the bloom. Upwelling winds then resumed, and the bloom was further dispersed by an influx of cold water. Throughout these oceanographic responses to changing winds, an intense bloom persisted in sheltered waters of the NE bay, where extreme blooms are most frequent and intense. Microscopic examination of surface phytoplankton samples from the central bay showed that spreading of the bloom from the NE bay and mixing with regional water masses resulted in significantly increased abundance of dinoflagellates and decreased abundance of diatoms. Similar dinoflagellate bloom incubation sites are indicated in other areas of the California Current system and other coastal upwelling systems. Through frequent bloom development and along-coast transports, relatively small incubation sites may significantly influence larger regions of the coastal marine ecosystems in which they reside.  相似文献   

17.
Tropical cyclones affect storm-dominated sediment transport processes that characterise Holocene shelf deposits in many shelf environments. A summary of cyclone-associated deposits in the Great Barrier Reef published by Larcombe and Carter [2004. Cyclone pumping, sediment partitioning and the development of the Great Barrier Reef shelf system: a review. Quaternary Science Reviews 23, pp. 107–135 indicates a pervasive northwards orientation of deposits on the lee side of reefs and other obstacles. In this paper, we describe the geomorphology of reef talus deposits found in the Gulf of Carpentaria and Arafura Sea, Australia, that we attribute to tropical cyclones. The orientation of these deposits is also indicative of a consistent, along-coast transport pathway. The deposits are located on the leeward side of submerged coral reefs; they are up to 10 m in thickness, comprised of re-worked carbonate sand and gravel and radiocarbon dating indicates that they are of Holocene age. An explanation for the consistent along-coast cyclone transport pathway is presented based on previously published hydrodynamic modelling results. These models illustrate how currents generated by the passage of a cyclone are asymmetric in plan view, such that stronger flows are generated between the eye of the cyclone and the coast. The result of the passage of many cyclones over geologic timescales is a net along-coast sediment transport pathway located on the inner- to mid-shelf, possibly extending over the entire length of northern Australia's coastline. This process provides an explanation for the observed sediment transport patterns on modern tropical continental shelves, as well as a basis for the interpretation of ancient tropical shelf deposits.  相似文献   

18.
The effect of offshore coral reefs on the impact from a tsunami remains controversial. For example, field surveys after the 2004 Indian Ocean tsunami indicate that the energy of the tsunami was reduced by natural coral reef barriers in Sri Lanka, but there was no indication that coral reefs off Banda Aceh, Indonesia had any effect on the tsunami. In this paper, we investigate whether the Great Barrier Reef (GBR) offshore Queensland, Australia, may have weakened the tsunami impact from the 2007 Solomon Islands earthquake. The fault slip distribution of the 2007 Solomon Islands earthquake was firstly obtained by teleseismic inversion. The tsunami was then propagated to shallow water just offshore the coast by solving the linear shallow water equations using a staggered grid finite-difference method. We used a relatively high resolution (approximately 250 m) bathymetric grid for the region just off the coast containing the reef. The tsunami waveforms recorded at tide gauge stations along the Australian coast were then compared to the results from the tsunami simulation when using both the realistic 250 m resolution bathymetry and with two grids having fictitious bathymetry: One in which the the GBR has been replaced by a smooth interpolation from depths outside the GBR to the coast (the “No GBR” grid), and one in which the GBR has been replaced by a flat plane at a depth equal to the mean water depth of the GBR (the “Average GBR” grid). From the comparison between the synthetic waveforms both with and without the Great Barrier Reef, we found that the Great Barrier Reef significantly weakened the tsunami impact. According to our model, the coral reefs delayed the tsunami arrival time by 5–10 minutes, decreased the amplitude of the first tsunami pulse to half or less, and lengthened the period of the tsunami.  相似文献   

19.
Pesticide runoff from agriculture poses a threat to water quality in the world heritage listed Great Barrier Reef (GBR) and sensitive monitoring tools are needed to detect these pollutants. This study investigated the utility of passive samplers in this role through deployment during a wet and dry season at river mouths, two near-shore regions and an offshore region. The nearshore marine environment was shown to be contaminated with pesticides in both the dry and wet seasons (average water concentrations of 1.3-3.8 ng L−1 and 2.2-6.4 ng L−1, respectively), while no pesticides were detected further offshore. Continuous monitoring of two rivers over 13 months showed waters flowing to the GBR were contaminated with herbicides (diuron, atrazine, hexazinone) year round, with highest average concentrations present during summer (350 ng L−1). The use of passive samplers has enabled identification of insecticides in GBR waters which have not been reported in the literature previously.  相似文献   

20.
Gorgan Bay is a semi-enclosed basin located in the southeast of the Caspian Sea, Iran. The bay is recognized as a resting place for migratory birds as well as a spawning habitat for native fish. However, apparently, no detailed research on its physical processes has previously been conducted. In this study, a 3D coupled hydrodynamic and solute transport model was used to investigate general circulation, thermohaline structure, and residence time in Gorgan Bay. Model outputs were validated against a set of field observations. Bottom friction and attenuation coefficient of light intensity were tuned in order to achieve optimum agreement with the observations. Results revealed that, due to the interaction between bathymetry and prevailing winds, a barotropic double-gyre circulation, dominating the general circulation, existed during all seasons in Gorgan Bay. Furthermore, temperature and salinity fluctuations in the bay were seasonal, due to the seasonal variability of atmospheric fluxes. Results also indicated that under the prevailing winds, the domain-averaged residence time in Gorgan Bay would be approximately 95 days. The rivers discharging into Gorgan Bay are considered as the main sources of nutrients in the bay. Since their mouths are located in the area with a residence time of over 100 days, Gorgan Bay could be at risk of eutrophication; it is necessary to adopt preventive measures against water quality degradation.  相似文献   

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