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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.
A holistic ecosystem simulation model has been developed for the Cumberland Basin and upper Chignecto Bay, a turbid macrotidal estuary at the head of the Bay of Fundy. This one-dimensional deterministic model has three compartments, three boundaries and three interacting submodels (physical, pelagic and benthic). Twenty-eight biological state variables represent broad functional groups of organisms and non-living organic carbon pools. All major components of the estuarine ecosystem are included. At the present stage of development, individual pelagic state variables give reasonable annual simulations which are in general agreement with available calibration data. Major problems remain with some benthic state variables, especially the subtidal ones about which little is known. In aggregate, the model performs well and output at the ecosystem level agrees with field observations. In the Cumberland Basin water column, annual community respiration exceeds phytoplankton net production (1–3 g C m−3) by a factor of 2–5 suggesting the importance of carbon imported from surrounding saltmarshes and the seaward boundary. Annual community respiration and microalgal net production (28 g C m−2) on the other hand are closely balanced in intertidal sediments. Respiration in subtidal sediments is entirely dependent upon sedimented carbon. The model supports the hypothesis that the Cumberland Basin is a heterotrophic ecosystem with low primary production which requires imported organic carbon to support the production and respiration of higher trophic levels.  相似文献   

3.
A probabilistic method of calculating the occurrence of oxygen-depleted water within a combined hydrothermal and water quality model was presented in this paper to investigate the environmental impact of eutrophication on the living resources. The method was applied to an eutrophicated shallow coastal bay in western Japan, where the occurrence of red tides at the water surface and the onset of bottom hypoxic waters are observed every summer. Both meteorology and freshwater inflow contribute to the development of stratification of the bay, thus limiting the dissolved oxygen supply to bottom waters. The resulting hydrodynamics enhances the development of oxygen-depleted bottom waters by transporting organic matter produced by algal blooms to the inner bay, where it decomposes and exerts high SOD. During August, about 60% of the inner bay is hypoxic for prolonged durations and as a result most of the benthic biota and fish die. The method used here is a very useful and informative way to evaluate the spatial and temporal damage and severity caused by hypoxia on living resources. Moreover, the model results agreed very well with the observed hydrodynamics, thermal structure and water quality data of the stratified bay. The model can be used for other lakes and bays where knowledge of temperature and density stratification is important for assessing water quality.  相似文献   

4.
The benthic response to nutrient loading of the water column was determined in the transition from early to mid-summer in a semi-enclosed, shallow estuarine ecosystem of the Baltic Sea. The procedure involved the inoculation of an in situ mesocosm with nitrogen and phosphorus to induce hypertrophic conditions, and comparison of this treated compartment with an untreated control. Sediment activity was assessed as oxygen turn-over, and measured in the laboratory with a simulated in situ polarographic flow-through method. Nutrient addition induced the development of pelagic organisms, particularly phytoplankton and protozoa, which resulted in turbidity within the water column. The latter appeared to depress benthic primary productivity. On the other hand, the greater organic matter load, upon sedimenting, caused increased biological respiration of the sediment. Chemical oxygen demand was unaffected by the increased organic matter input.  相似文献   

5.
An ecosystem model is used to calculate and summarize carbon budgets within the Ems Estuary, The Netherlands. The similarity between model calculations and field data is established using a validation procedure. Model results show that the seaward boundary concentration for suspended matter is important in determining whether an estuary is an importer or exporter of carbon. Lowered boundary concentrations of suspended matter enhance pelagic primary production, but reduce sedimentation and hence the carbon flux from pelagic to benthic systems.  相似文献   

6.
Effects of spilled oil on microbial communities in tidal flats were examined by use of a simulator for a tidal flat ecosystem. The simulator is composed of a wave generator, a tide control device, and a tidal flat. Sediment for the tidal flat was obtained at a natural tidal flat in Hiroshima Bay, Japan. After stabilizing the benthic organisms, fuel oil C was added to the surface of the flat at 1 lm(-2). Although the total number of micro-organisms remained at 1.5-3.5 x 10(9) cells g(-1) dry sediment irrespective of the addition of oil, bacterial communities which were analyzed based on the 16S rDNA showed clear changes after the addition of fuel oil C and after a subsequent recovery period. Bacterial colonies were randomly isolated from the oil-supplemented sediment during the experiments, and the isolates were examined for susceptibility to hydrocarbons in order to screen the oil-susceptible bacteria. The proportion of oil-susceptible bacteria in the isolates decreased with the addition of the oil. Oil-susceptible bacteria showed an inability to assimilate petroleum compounds as well as an inhibition of growth. The possibility of using oil-susceptible bacteria as an indicator of bioremediation in tidal flats was discussed.  相似文献   

7.
Nitrogen budgets and predominant benthic organisms were examined at a matured artificial tidal flat of Osaka Nanko bird sanctuary and an artificial young tidal flat of Hannan Second District, Osaka Bay, Japan. At the Osaka Nanko bird sanctuary, indexes of the quality of the bottom sediment increased over the time course and no abiotic area was observed in the macrobenthic fauna. Dissolved inorganic nitrogen imported into the tidal flat changed its form and was exported in the form of dissolved organic nitrogen. As a result, total nitrogen was trapped at the tidal flat at an average rate of 138 mgN m(-2)day(-1). At the young tidal flat of Hannan Second District net exchange of nitrogen varied markedly among 2000, 2001, 2002 and 2003. In September 2000 when only 5 months had passed after construction, the tidal flat functioned as a site of source for nitrogen. However, it changed as a sink for nitrogen in 2001-2002 in relation to the growth of seaweeds (Ulva spp. and Gracilaria vermiculophylla) and clams (Tapes philippinarum). In 2003 nitrogen was again released from the artificial tidal flat due to the decrease of biomass of the dominant organisms. Comparing the nitrogen budget between the two sites on a per unit time and area basis, net exchanges of nitrogen by tidal exchange were apparently low and relatively constant at the tidal flat of Osaka Nanko bird sanctuary. This suggests that the aged artificial tidal flat of Osaka Nanko bird sanctuary has a stable ecosystem compared to the young artificial tidal flat of Hannan Second District.  相似文献   

8.
Competition between pelagic and benthic microalgae for phosphorus and light   总被引：2，自引：0，他引：2  
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9.
浅水湖泊中的初级生产者主要由分布在底栖生境中的底栖植物和生活在敞水生境中的浮游植物组成.底栖植物主要包括维管束沉水植物和底栖藻类等,浮游植物则主要为浮游藻类.贫营养浅水湖泊湖水营养盐浓度低,透明度高,底栖植物因能直接从沉积物中获取营养盐,往往是浅水湖泊的优势初级生产者.随着外源营养盐负荷的增加,湖水中的营养盐浓度不断升高,浮游植物受到的营养盐限制作用减小,加上其在光照方面的竞争优势,逐步发展成为湖泊的优势初级生产者,湖泊逐步从底栖植物为优势的清水态转变为浮游植物为主的浑水态,即稳态转换.在稳态转换过程中,浅水湖泊生态系统结构与功能发生了一系列变化,本文综述了浅水湖泊沉积物性质和生物(浮游植物、底栖植物、底栖动物和鱼类等)群落结构的变化,分析了这些变化对底栖植物、浮游植物之间竞争优势和底栖敞水生境间磷交换的影响,探讨了富营养化驱动的底栖敞水生境耦合过程变化和稳态转换机理.了解浅水湖泊底栖敞水生境耦合过程与稳态转换机理对富营养化浅水湖泊修复有重要意义.富营养化浅水湖泊修复实际就是重建其清水态,在制定修复目标时应该关注评价清水态的指标,如透明度、浮游植物生物量、底栖植物的覆盖度或优势度等.在开展湖泊修复技术研发与工程应用时,应该重点关注对底栖敞水生境耦合有重要影响的关键技术,如沉积物磷释放和底栖生物食性鱼类控制以及底栖植物(尤其是沉水植物)恢复等有关技术.  相似文献   

10.
Microbial activity in permeable tidal flat margin sediments is enhanced by two main processes. First, organic matter is supplied by rapid sedimentation at prograding tidal flat margins. Second, surface and deep pore water advection lead to a replenishment of the dissolved organic matter and sulfate pools. Increasing microbial activity towards the low water line is reflected in sulfate and methane profiles as well as in total cell numbers, sulfate reduction rates, and remineralization products. The impact of high sedimentation rates on pore water biogeochemistry is confirmed by inverse modeling reproducing the depth profiles obtained by measurements. In central parts of the tidal flats, low sedimentation rates and pore water flow velocities limit microbial activity despite the high availability of electron acceptors for microbial respiration such as sulfate. Therefore, tidal flat margins with high microbial activity are of special importance for budgeting biogeochemical cycling in tidal flat areas.  相似文献   

11.
A history of water pollution and countermeasures for water purification in Dokai Bay, Japan are reviewed. Now, Dokai Bay suffers from the occurrences of red tides and oxygen-deficiency in summer. In order to prevent the occurrences of red tides and oxygen-deficiency, an ecological numerical model has been developed. The model experiments forecast that when the phosphorus or nitrogen load from land will be cut by 90% or 95%, respectively, red tides and oxygen-deficiency will not occur in Dokai Bay. If the industrial and sewage facilities are not sufficient to cut the nutrients load to the necessary degree, we have to consider other countermeasures such as cultivating bivalves and algae in order to decrease the nutrients concentration in the bay. International co-operation related to coastal zone management is also discussed.  相似文献   

12.
《Marine pollution bulletin》2012,64(5-12):237-242
Terrigenous loading into enclosed water bodies has been blamed for eutrophic conditions marked by massive algal growth and subsequent hypoxia due to decomposition of dead algal cells. This study aims to describe the eutrophication and hypoxia processes in a semi-enclosed water body lying near a big metropolis. Phosphorus mass balance in a small inlet, Ohko Inlet, located at the head of Hiroshima Bay, Japan, was quantified using a numerical model. Dissolved inorganic phosphorous inflow from Kaita Bay next to the inlet was five times higher than that from terrigenous load, which may cause an enhancement of primary production. Therefore, it was concluded that not only the reduction of material load from the land and the suppression of benthic flux are needed, but also reducing the inflow of high phosphorus and oxygen depleted water from Kaita Bay will form a collective alternative measure to remediate the environmental condition of the inlet.  相似文献   

13.
Terrigenous loading into enclosed water bodies has been blamed for eutrophic conditions marked by massive algal growth and subsequent hypoxia due to decomposition of dead algal cells. This study aims to describe the eutrophication and hypoxia processes in a semi-enclosed water body lying near a big metropolis. Phosphorus mass balance in a small inlet, Ohko Inlet, located at the head of Hiroshima Bay, Japan, was quantified using a numerical model. Dissolved inorganic phosphorous inflow from Kaita Bay next to the inlet was five times higher than that from terrigenous load, which may cause an enhancement of primary production. Therefore, it was concluded that not only the reduction of material load from the land and the suppression of benthic flux are needed, but also reducing the inflow of high phosphorus and oxygen depleted water from Kaita Bay will form a collective alternative measure to remediate the environmental condition of the inlet.  相似文献   

14.
Spartina alterniflora is ecologically important in its original habitat; however, it has caused controversy since it was introduction into China (now it has been spreading rapidly on the Jiangsu, Shanghai, Zhejiang and Fujian coasts). The purpose of the present contribution is, on the basis of an analysis and synthesis of existing data sets, to evaluate the environmental-ecological effects of S. alterniflora, and to identify the relevant scientific problems that require further research in the future. Investigations have shown that, by reducing the near-bed shear stress associated with tidal currents, S. alterniflora can enhance the settling flux of suspended sediment and deposition rate on the tidal flats over the region. Further, field survey and analysis indicate that the S. alterniflora salt-marsh has a high primary production and provides a new type of habitat for the native benthic fauna. Some macro-, meio- and micro-fauna that used to live in the native salt-marshes have adapted to the S. alterniflora salt-marsh, forming a new ecosystem. Under the influences of a number of background factors, such as latitude variations and the coastal type, the environmental-ecological changes induced by Spartine have regional differentiations. To the north of Hangzhou Bay, with a high position of the pre-Holocene stratum base, a large width of the tidal flats, and a gentle bed slope, only a small part of the intertidal zone is occupied by the S. alterniflora salt-marsh. Here, the S. alterniflora salt-marshes mainly play a positive role in coastal protection and ecosystem functioning. In contrary, to the South of Hangzhou Bay, The pre-Holocene deposits are situated in relatively deeo waters, and the width of the tidal flats formed within coastal embayments is relatively narrow. As such, the expansion of S. alterniflora has squeezed the living space of other intertidal organisms, thus has a negative ecological effect. Therefore, the regional differentiation of the Spartina effects should be sufficiently considered in coastal development and management. Furthermore, in order to predict the future evolution of the S. alterniflora wetlands over the region, in addition to in situ monitoring and measurements, an ecosystem dynamic model should be established, taking into account the coupling of the rerrestrial and marine environmental-ecological processes.  相似文献   

15.
Perturbation of regional ocean tides due to coastal dikes   总被引：1，自引：0，他引：1  
The tidal regime modeling system for ocean tides in the seas bordering the Korean Peninsula is designed to cover an area that is broad in scope and size, yet provide a high degree of resolution in coastal development areas, including the Saemangeum area in the eastern Yellow Sea and the Ariake Sea in Japan, where serious environmental problems have occurred after the completion of interior tidal dikes. With this simulation system, we have estimated the changes in tidal regime due to barriers at Saemangeum and Isahaya Bay in the Ariake Sea. Some results in terms of perturbations in tidal elevations due to the construction of coastal dikes are presented and discussed.  相似文献   

16.
Fluxes of dissolved inorganic nutrients: NH4+, NO2-, NO3-, PO4(3-) and Si(OH)4 from nearshore sediments of Gazi Bay were measured in situ within mangrove, seagrass and coral reef biotopes using benthic flux bell-jar chambers of cross-sectional area 0.066 m2 and volume 0.0132 m3. The objectives were: (1) to determine the influence of benthic fluxes, fluvial discharge and seasonal variations on the nutrient budget in the Bay waters; (2) to determine the effect of tidal and spatial variations on nutrient loads in the water column and (3) to establish the relative importance of the nutrient sources with regard to total community production of the Bay. The directly measured fluxes ranged from -270 to +148 micromol NH4+-N/m2/h; -60 to +63 micromol NO2(-)-N/m2/h; -79 to +41 micromol NO3(-)-N/m2/h; -79 to +75 micromol PO4(3-)-P/m2/h and +30 to +350 micromol Si(OH)4-Si/m2/h for and respectively. It was established that benthic fluxes are the major sources of dissolved inorganic NH4+, NO2- and Si(OH)4 while fluvial sources are important for NO3- and PO4(3-) into Gazi Bay waters. Seasonal variations had an appreciable effect on the PO4(3-) fluxes, N:Si ratio, river nutrient discharge, plankton productivity and important environmental factors such as salinity and temperature. Tidal and spatial variations had no significant effect on nutrient concentrations and net fluxes within the water column. The results imply that benthic fluxes are largely responsible for the nutrient dynamics of the nearshore coastal ecosystems especially where direct terrestrial inputs do not contribute significantly to the nutrient budget.  相似文献   

17.
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18.
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19.
The Hangzhou Bay is a macro-tidal bay located to the south of the Changjiang estuary in China. Along its northern shore, a large-scale tidal channel system has developed, which includes a main northern tidal channel, with a length of more than 50 km and a width up to 10 km, and a secondary southern tidal channel. A process-based morphodynamic model, incorporating the cohesive sediment transport module of Delft3D, is used to analyze the physical processes and mechanisms underlying the formation and evolution of this tidal channel system. The results show that spatial gradients of flood dominance, caused by boundary enhancement via current convergences, is responsible for the formation of the channel system, due to a combination of the various factors such as funnel-shaped geometry hindering associated with the presence of islands, and flow deviation by the southern tidal flat and so on. The model results agree well with the real morphological features. This study also indicates that the reclamation of the southern tidal flat imposes a profound influence on the morphological evolution of the tidal channel system in the Hangzhou Bay. It is feasible to use the model to simulate long-term estuarine morphological changes with cohesive sediment settings.  相似文献   

20.
The Bay of Fundy in eastern Canada has the highest tides in the world. Harnessing the tidal energy in the region has long been considered. In this study, the effects of tidal in-stream energy extraction in the Minas Passage on the three-dimensional (3D) tidal circulation in the Bay of Fundy (BoF) and the Gulf of Maine (GoM) are examined using a nested-grid coastal ocean circulation model based on the Princeton Ocean Model (POM). The nested-grid model consists of a coarse-resolution (~4.5 km) parent sub-model for the GoM and a high-resolution (~1.5 km) child sub-model for the BoF. The tidal in-stream energy extraction in the model is parameterized in terms of nonlinear Rayleigh friction in the momentum equation. A suite of numerical experiments are conducted to determine the ranges of extractable tidal in-stream energy and resulting effects on the 3D tidal circulation over the Bay of Fundy and the Gulf of Maine (BoF-GoM) in terms of the Rayleigh friction coefficients. The 3D model results suggest that the maximum energy extraction in the Minas Passage increases tidal elevations and tidal currents throughout the GoM and reduces tidal elevations and circulation in the upper BoF, especially in the Minas Basin. The far-field effect of tidal energy extraction in the Passage on the 3D tidal circulation in the BoF-GoM is examined in two cases of harnessing tidal in-stream energy from (a) the entire water column and (b) the lower water column within 20 m above the bottom in the Passage. The 3D model results demonstrate that tidal in-stream energy extraction from the lower water column has less impact on the tidal elevations and circulation in the BoF-GoM than the energy extraction from the whole water column in the Minas Passage.  相似文献   

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