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1.
A risk assessment of Tributyltin (TBT) in Tokyo Bay was conducted using the Margin of Exposure (MOE) method at the species level using the Japanese short-neck clam, Ruditapes philippinarum. The assessment endpoint was defined to protect R. philippinarum in Tokyo Bay from TBT (growth effects). A No Observed Effect Concentration (NOEC) for this species with respect to growth reduction induced by TBT was estimated from experimental results published in the scientific literature. Sources of TBT in this study were assumed to be commercial vessels in harbors and navigation routes. Concentrations of TBT in Tokyo Bay were estimated using a three-dimensional hydrodynamic model, an ecosystem model and a chemical fate model. MOEs for this species were estimated for the years 1990, 2000, and 2007. Estimated MOEs for R. philippinarum for 1990, 2000, and 2007 were approximately 1–3, 10, and 100, respectively, indicating a declining temporal trend in the probability of adverse growth effects.A simplified software package called RAMTB was developed by incorporating the chemical fate model and the databases of seasonal flow fields and distributions of organic substances (phytoplankton and detritus) in Tokyo Bay, simulated by the hydrodynamic and ecological model, respectively.  相似文献   
2.
A new coastal marine ecosystem model was developed, which was composed of pelagic and benthic ecosystems, and was applied to Mikawa Bay, Japan. This model deals with variations of biochemical and physical interactions among dissolved oxygen and C–N–P species (composition formed out of carbon, nitrogen and phosphorus elements) so that it resolves the flux dynamics of carbon, nitrogen, phosphorus and oxygen elements. The physical and biochemical mechanism figured in this model is constructed for the purpose of simulating the estuarine lower trophic ecosystem, in areas where the sea was too deep for light to reach the sea-bottom. As a result of coupling the benthic with pelagic system, the effect of process of sedimentation and nutrient diffusion back to the pelagic system could be indicated. In addition, by implementing the tidal flat ecosystem model's calculation result, the integrated model can include the effect of water purification in tidal flats where the light can reach the sea-bottom, and where sea-weed, sea grass and benthic algae exist. In this study, the model indicates that oxygen-depleted water exists at the sea-bottom especially in summer mainly caused by an increase of oxygen consumption in the benthic system and a decrease of the vertical mixing water process. Furthermore, by comparing the case – with the tidal flat ecosystem model and the case without it, the effect of water purification of tidal flat estuaries was indicated. From the viewpoint of a short time scale, the tidal flat has the potential to restrict red tide (rapid increase of phytoplankton), and from the viewpoint of a long time scale, it restricts the sedimentation of detritus. Restricting the sedimentation prevents oxygen-depleted water occurring in the coastal marine system of Mikawa Bay.  相似文献   
3.
An ecosystem model was used to evaluate the effects of reclaiming seagrass beds and creating artificial shallows with seagrass beds to mitigate the effects of the reclamation. The applied model can simulate the pelagic and benthic ecosystems including seagrass beds and tidal flats. The objectives of this study were (a) to investigate the likelihood of cultivating and maintaining seagrass beds in artificial shallows (Part 1), and (b) to understand the effects of the reclamation of seagrass beds and the creation of artificial shallows on the water quality in the estuary (Part 2). In Part 1, first, the nutrient turnover rates due to both biochemical and physical processes in the natural seagrass beds where reclamation is proposed were analyzed. Biological processes rather than physical processes were the most significant driving forces of nutrient cycles in seagrass beds. Second, the effects of filter feeding benthic fauna (suspension feeders) in the seagrass beds were analyzed. The scenario with suspension feeders resulted in higher transparency of the water column (8.7% decrease in the light attenuation coefficient) and an increase in nutrient supply (24.9% increase in NH4-N in the water column) contributing to the high specific growth rate of seagrass. Third, the specific growth rate of seagrass on the proposed artificial shallows was measured. The value on the artificial shallows set at a depth of datum line minus 0.8 m (D.L. − 0.8 m) was approximately the same as that of the natural seagrass beds. In Part 2, first, water quality in the estuary was compared among the scenarios with/without natural seagrass beds and artificial shallows. Then, the defined values of the water purification capability of (a) artificial shallows with/without seagrass beds, and (b) natural seagrass beds per unit area were evaluated. The reclamation of the natural seagrass beds resulted in a decrease of the removal of phytoplankton and detritus from the pelagic system (i.e. resulted in a loss in the purification rate). In contrast, the creation of artificial shallows resulted in an increase of the removal of phytoplankton and detritus from the pelagic system (i.e. resulted in a gain in the purification rate). Based on an annual average, approximately twice as much phytoplankton was removed from the artificial shallows at the depth D.L. − 0.8 m, than at the depth, D.L. − 1.5 m, and the artificial shallows with seagrass beds removed pelagic DIN and DIP at a rate 120% higher than that without seagrass beds.  相似文献   
4.
Sensitivity analysis of a coastal marine ecosystem   总被引：1，自引：0，他引：1  
An ecosystem with four compartments, i.e. PO4-P, phytoplankton, zooplankton and detritus, in a coastal region was considered. Sensitivity analysis of a phosphorus flow model in well-mixed water without currents concludes that (1) the maximal photosynthetic rate,V m , in Michaelis-Menten relation plays an important role in the distribution of biomass among compartments but the half saturation constant,K s , is not so important, (2) the natural death rate of phytoplankton is important for the ecosystem, (3) the natural death rate of zooplankton is also effective on the ecosystem.A numerical experiment was also performed on the ecosystem with four compartments are also studied using a dynamical barotropic model of tidal currents of Mikawa Bay (Japan). Diffusion coefficient in diffusion equation plays the role of a linear smoothing parameter in the horizontal distribution of compartment. On the other hand, perturbations of biological parameters cause nonlinear variations in the horizontal distribution of compartment.  相似文献   
5.
A 3-D chemical fate prediction model (FATE3D) was applied to predict the dioxin concentrations in the seawater of Tokyo Bay, Japan. The simulations were carried out for a period of one year (from September 2002 to August 2003). Parameters such as meteorological data, flow field conditions, concentrations and sinking rates of organic particulate matter, initial and boundary conditions, and loading fluxes and physico-chemical properties of dioxins were used as the model inputs.The simulation results compared favorably with the field measurements of dioxin concentrations in the bay for both the particulate and dissolved phases, indicating the validity and predictive capability of the model. Furthermore, the differences in the seasonal cycles and distributions between the particulate- and dissolved-phase dioxins in the bay were estimated from the simulation results.However, the particulate-phase dioxin concentrations in the bottom layers (+1 m from the bottom) were underestimated, probably because the resuspension process was not taken into account in the model. The improvement of the model's predictive capability, including the resuspension process, shall be the focus of our next study.  相似文献   
6.
Distributions and characteristics of water mass and chlorofluorocarbons (CFCs) in the North Pacific are investigated by using a General Circulation Model (GCM). The anthropogenic CO2 uptake by the ocean is estimated with velocity fields derived from the GCM experiments. The sensitivity of the uptake to different diffusion parameterizations and different surface forcing used in the GCM is investigated by conducting the three GCM experiments; the diffusive processes are parameterized by horizontal and vertical eddy diffusion which is used in many previous models (RUN1), parameterized by isopycnal diffusion (RUN2), and isopycnal diffusion and perpetual winter forcing for surface temperature and salinity (RUN3). Realistic features for water masses and CFCs can be simulated by the isopycnal diffusion models. The horizontal and vertical diffusion model fails to simulate the salinity minimum and realistic penetration of CFCs into the ocean. The depth of the salinity minimum layer is better simulated under the winter forcing. The results suggest that both isopycnal parameterization and winter forcing are crucial for the model water masses and CFCs simulations. The oceanic uptake of anthropogenic CO2 in RUN3 is about 19.8 GtC in 1990, which is larger by about 10% than that in RUN1 with horizontal and vertical diffusive parameterization. RUN3 well simulates the realistic water mass structure of the intermediate layer considered as a candidate of oceanic sink for anthropogenic CO2. The results suggest that the previous models with horizontal and vertical diffusive parameterization may give the oceanic uptake of anthropogenic CO2 underestimated. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   
7.
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8.
Current records obtained in the inshore region along the Fukushima coast are analyzed. The existence of periodical current fluctuations whose period is about 100 hours and whose amplitude is as large as 15–25cm s–1 is recognized. Auto-spectral analyses are made also for sea level, atmospheric pressure and wind records. Each spectrum has significant peaks at the similar period to the current spectrum. The wind spectrum has a broad peak compared with the current. The periodical current fluctuations propagate southward with speed of 3–5 km h–1. These propagation speeds seem to correspond to those of the second-and third-mode shelf waves.  相似文献   
9.
To understand when oxygen-depleted waters occur, how they develop and when they dissipate in inner Tokyo Bay, realistic simulations were attempted with fine spatial and temporal resolution by applying realistic time dependent external forcing. A 3D hydrodynamic model was driven by time-dependent external forcing factors/parameters such as solar radiation, air temperature, relative humidity, wind velocity, and fluvial discharge, under the open boundary conditions of 1995. A simulated time series of salinity and temperature agreed fairly well with observed data, except in summer. The model failed to reproduce the development of the surface mixed layer in summer. Several sensitivity analyses on the external forcing parameters such as wind velocity and vertical diffusivity were conducted to reproduce the mixed layer. However, changing these parameter values did not improve the model results.  相似文献   
10.
Water temperature, salinity, nutrient concentrations and the composition of the plankton community were recorded at three stations in inner Tokyo Bay over a period of 328 days (from June 8, 1995 to April 30, 1996) with a nominal sampling frequency of once per day. Inspection of the results revealed that the data could be divided into two blocs as an aid to analysis: the period from June to October was characterized by the development of stratification of temperature and salinity (stratification period), and November to March was characterized by uniform temperature and salinity in the water column due to vertical mixing (mixing period). Oxygen-depleted water forms in the bottom layer during the stratification period, but vertical mixing of the water column, due to changing wind and rainfall conditions caused by passing weather fronts, results in the breakdown of the oxygen-depleted water mass. Nutrient loads are high in the surface water due to the freshwater supply, but occasional pulses of primary production cause a depletion of phosphate in the surface water, suggesting that the phosphorus becomes a limiting nutrient for phytoplankton growth in this period. Several short-term peaks of plankton abundance (blooms) occurred as responses to temporal changes in water quality from June to November, with consequent species succession. Significant fluctuations in the densities of the diatom Skeletonema costatum and several species of ciliates corresponded to the daily changes in the physical and chemical characteristics of the coastal environment. During the mixing period, when water temperature and solar radiation decreased, there were no short-term variations in water quality and although nutrient concentrations gradually increased from November to February, primary production remained low. This study shows that the short-term dynamics of the phytoplankton community are closely coupled to fluctuations in environmental forcing, and that the degree of coupling is stronger during periods when solar radiation is greater. The results provide a novel typological understanding of seasonal plankton dynamics in a shallow, eutrophicated marine embayment, and suggest how such systems may be treated in simulation modeling.  相似文献   
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