It is important that flocculation and settling of the suspended sediment (SS) on the formation mechanism of the bottom mud in the tidal river. In this study, the field observation on the settling rate was done in one tide in the tidal river of the Chikugo River, Japan at a spring tide. The new techniques for the measurement of the settling rate of SS were developed to compare settling velocity with the turbulence kinetic energy, SS concentration, chl-a/SS, and salinity. As a result of this study, it is clarified that the reason of the increase of the settling rate around the salinity front was owing to the mixing of the SS with algae, salinity intrusion and the rapid decrease of the turbulent around high tide.

View full abstract

Temporal variation of phytoplankton in the Chikugogawa estuary was observed for two weeks in the summer of 2009. The concentration of chlorophyll a in surface water was the highest two days after the neap tide, and that of pheophytin was the lowest during this time. The level of concentration of pheophytin increased gradually when the high tidal velocities produced strong vertical mixing. A strong correlation existed between pheophytin a and the suspended sediment concentration. Therefore, it is inferred that phytoplankton grows at the surface during the neap tide and that they settle to the bottom of the estuary to form detritus as the light penetration of the water column is reduced by the suspended sediment. It is suggested that detritus is resuspended with fine sediment owing to strong mixing during spring tide.

View full abstract

A mechanism of the oxygen-depleted water formation near the head of the Ariake Bay is presented based on the field observation data taken by Seikai National Fisheries Research Institute (2009). The first formation of oxygen-depleted water occurred just after big discharges from rivers due to strong salinity stratification and massive Skeletonema sp. growth. The second formation was occurred in August when thermal stratification was developed and Chattonella sp. grew rapidly by taking nutrients in the bottom with vertically migration. A numerical model to simulate these processes was constructed using DELFT3D. The model reproduced the field data very well and revealed that degradation of detritus derived from phytoplankton in the water column and sediment was the most important for the oxygen consumption process.

View full abstract

The blue tide began to occur every year after 2002 in the head of Osaka Bay. It is important to investigate an occurrence of the blue tide in the field. Therefore occurrences of the blue tide and these range were confirmed by visual observation and hearing investigation after 2005. In a result, occurrences of the blue tide counted up to 11. While, temporal and spatial variations of water temperature, salinity and DO were simultaneously investigated to clarify the mechanism of the blue tide. The analysis of observed seawater suggested that an occurrence and a range of the blue tide were closely related to a stratified intensity defined as a vertical gradient of density of seawater and oxygen depression.

View full abstract

Recently, an increase in the load from the land and a food scatter of aquaculture causes eutrophication in IMARI Bay. Therefore, red tides have been generated. It is necessary to decrease the red tide. So, as a basic research, we clarify the characteristics of flow structure and water quality by means of field observations and a numerical model. As a consequence, it is clear that flow structure around bay mouth is very complex. Bay water flows out in the upper layer during ebb tide, and outer sea water flows into the lower layer during flood tide. It is realized that the tidal exchange is strong comparatively in the western part of the bay, while it is weak in the central and south-eastern part.

View full abstract

The simultaneous estimation of SS and Chlorophyll-a (Chl.a) in shallow water through remote sensing was tried in this study. Lake Teganuma located in Chiba Prefecture was selected as a test site. Twelve spectral reflectance / Chl.a data sets were acquired using outboard boat in the lake on 28 May 2009 and 22 Oct. 2008. These data sets were related to SS or Chl.a using a simple single band or two band ratio models. As a result, a statically significant correlation was observed between "a reflectance of the simulated ALOS/AVNIR-2 Band 4 (760-890nm)" and "SS", or "reflectance ratio of the simulated AVNIR-2 band 3 (610-690nm) and band 4" and "Chl.a". These models were validated though the ALOS/AVNIR-2 data and the buoy data set on 20 May 2008 and 28 Oct. 2009.

View full abstract

Oxygen consumption by bottom sediment in a eutrophied port and harbor is modeled based on field investigation. The model consists of factors of biological contribution and chemical-physical contribution. It is presented that these factors can be estimated by water temperature and dissolved oxygen above the sea bottom. Through modeling sediment oxygen consumption it is found that a penetration depth of oxygen is a useful parameter to represent sea bottom environment as a remediation. Further, estimation method of penetration depth of oxygen is improved to take into the change of the dissolved oxygen above sea bottom consideration.

View full abstract

In order to elucidate a link between the sediment oxygen consumption (SOC) and the benthic environment, field observations of water quality and sediment environment were carried out during summer to autumn at 4 sites in the head of Tokyo Bay in 2009. SOC was observed by chamber methods after sampling by using fluorescent DO meter at a laboratory. The benthic environment was observed by a CN ratio and the quinine profile methods. Water quality on the seabed was also measured including DO, sulfide and nutrients at the same time. SOC was positively correlated with quinine concentrations. This correlation was the same level as water temperature, salinity and sulfide. From the long-term oxygen consumption experiments, influence of sediment microbial community was also confirmed.

View full abstract

To determine the recovery process of hypoxia of bottom water at northwestern Tokyo Bay, Japan, the seawater characteristics, climate condition and flow regime have been monitored for three years. Following results were obtained that 1) the recovery process of hypoxia could be triggered by the intrusion of high density and oxygen rich bottom water from the bay mouth, 2)the typical velocity of those water mass was estimated as 2.7(±1.2) km/day from the change of the isopycnic line, and 3) associated increment of the density and oxygen recovery were observed with short term tidal motion. Thus, the recovery process of the hypoxia of bottom water could be influenced and triggered by the wind and the flow regime of concerned area.

View full abstract

We conducted field observations in relation to hypoxia which occurs in strongly enclosed waters, such as ports and harbors, and examined generation mechanism and movement of hypoxia. Diurnal variations in hypoxia were driven by tide and wind in the strongly enclosed waters in the head of Osaka Bay. It was found that processes of the organism decomposition, oxygen consumption and carbon dioxide generation were different in and out of the ports. In the spring and summer when the water column is stratified, surface water absorbs CO2 and bottom water stores CO2 in strongly enclosed waters. On the other hand, in the end of summer, the stored CO2 upwells to the surface and causes spontaneous emission because the north wind induces the upwelling.

View full abstract

The characteristics of water environment of Yong-won Bay in Korea, where the coastal area has been largely reclaimed to construct Busan New Port, were investigated by means of field observation and numerical simulation. Low sea water exchange rate and stratification due to the residence of fresh water are found to be main causes of anoxic water in the western part of Yong-won Bay. Observed sediment which contains a lot of fresh organic matter, is possibly concerned with weak tidal current in the western part. Water-holding capability of organic sediment correlates with maximum current velocity. It seems possible to predict the sediment property by simulated current velocity.

View full abstract

This study is aimed at numerically discussing the formation mechanism of intermittent subsurface-layer hypoxia in summer season in Ise bay. The long-term variation of hypoxia was examined by using a quasi three-dimensional numerical ocean model with MOVE-WNP data, which are dataset of an ocean variational estimation system in Western North Pacific. The numerical result revealed that hypoxia in the subsurface-layer was formed by the intermittent intrusion of oceanic water into the bottom layer of the bay. The MOVE-WNP data were also confirmed to be useful in comprehending the influence of ocean on internal structure in a bay through the numerical experiments.

View full abstract

The environmental characteristics of seabed sediment in Isahaya Bay were investigated comprehensively in summer of 2009. The sediment was composed of the grain size from medium silt to fine silt. The value of IL was totally higher than 10 % and especially the organic pollution advanced near the both drain gates of the reclamation dike. The value of AVS was larger than the standard of water for fisheries and the sediment at the head of the bay was in the anaerobic condition. The velocity of the sediment oxygen consumption took the largest value near the south drain gate. The relationships of AVS, NH₄-N, NO₂-N+NO₃-N and PO₄-P versus ORP revealed that the seabed sediment had been in sulfate reduction and PO₄-P had been released in the sediment.

View full abstract

A field survey and laboratory analyses of sediment quality in the eastern part of Osaka Bay are carried out to clarify their characteristics and influence on the dynamics of hypoxia. Nitrogen, phosphorus and sulfur cycling in the coastal water and sediment are modeled with a focus on the formation of hydrogen sulfide in hypertrophic sediment and its release to the bottom water. In the calculated results the oxygen consumption in the bottom water by the release of sulfide is much larger than the direct oxygen consumption by the sediment in the northern port of the bay. Without the release of sulfide, the hypoxic water area would be estimated to be limited in and near the port area of the head of the bay. The wide spreading of hypoxia in the eastern part of the bay would be contributed largely by the sulfide release.

View full abstract

In coastal areas around big cities such as Tokyo Bay, intertidal flats decreased due to man-made reclamation lands constructions. Such a loss of tidal flats make, water quality environments deteriorated. In the study, we carried out field studies to estimate nutrient fluxes between inter tidal sediment and overlying water and intertidal water and neighbor sea water. In conclusion, we found the following results. (1) Function of this tidal flat is net source of phosphorus and net sink of nitrogen and chlorophyll-a in summer. And function of net source of phosphorus in summer changes to net sink of that in winter. (2)The fluxes of phosphorus and nitrogen from the intertidal sediment are 20% and 87% of the fluxes through the changes between tidal flat and neighbor sea water.

View full abstract

The aim of this study is to investigate a movement mechanism of organic fine particles (OFP) in a sand column, which is a useful knowledge in a restoration of aggravated tidal flat and a construction of man-mad sandy tidal flat. It was found that Hagen-Poiseuille equation could express the characteristics of flow in the sand column; and the pressure loss inside the sand column considering OFP could be formulated theoretically. The movement of OFP in the sand column estimated from the formula was verified by experiments. Moreover, the organic properties of OFP strongly affected the movement; namely, decomposed OFP were easy to travel through the sand column.

View full abstract

The Yatsu Higata wetland is one of the most significant tidal flat areas remaining in Japan. Although the site was officially recognized as an important wetland for migratory bird species in 1993 when it was registered as the Ramsar Convention, the extraordinary growth of Ulva sp. (sea lettuce) in recent years has severely impacted the ecology of the area and has resulted in the widespread death of benthic organisms such as clams and sandworms. Conversely, the crop of laver has decreased along the periphery of the tidal flat area.. This study examined the underlying causes of the increase and decrease in the crops of Ulva sp. and laver populations in the field, respectively. In addition, numerical simulations were performed to estimate the flow movement of Ulva sp. circulating in the inner Tokyo Bay area.

View full abstract

The mechanism of how mahogany clams could live at the depth of over 50 cm in tidal flat was examined by field and laboratory experiments. The mahogany clams bred in the different depth of tidal flat (10 to 50 cm). And the migration of mahogany clams in the tidal flat was investigated. It was understood that mahogany clams could live two months without feeding and breathing through the tidal flat surface. Moreover, survival rate of mahogany clam bred near the lowest groundwater level was higher than that near the tidal flat surface (0 to 10 cm).

View full abstract

Observation and laboratory experiments were performed to understand the re-suspension mechanism of organic mud under salinity variation at an estuarine bed. The organic mud is transported upstream under the separation into different types of organic matter. The re-suspension flux of organic mud depends on not only the shear stresses and organic properties but also surface water salinity. The re-suspension flux of organic mud was separated into fresh water and saline water components. The re-suspension flux also depends on the content rate of POCs originated in oil and fat/primary production. The trend of turbidity in the Tenma River can be almost explained with the re-suspension formula of organic mud considering the salinity effect.

View full abstract

The present study aims at examining the processes of benthic habitat selection as induced by optimal burrowing and geoenvironnmental gradients. We utilized a newly developed eco-geoenvironment-water tank in order to clarify the response of benthos to a wide variety of geoenvironments involving both optimal and critical conditions, OP and CR, for burrowing of sand-bubbler crab, Scopimera globosa. The results indicate that the benthos placed in the OP swiftly started burrowing, by contrast, the benthos placed in the CR migrated toward the OP to burrow there. Furthermore, the predicted patch formation based on our proposed optimal-burrowing-model is found to be well consistent with what has been manifested in the field. These results demonstrate that the burrowing benthos actively selects the suitable geoenvironments for their burrowing, thereby generating patch formation. Hence, the present finding will alter the current perspective of habitat selection based on optimal-foraging-model and will facilitate a new horizon of ecohabitat management in the future.

View full abstract

Referring field observation data on tree configurations consisting of coastal forests and invoking knowledge developed in tree morphology, a typical structure of coastal pine trees was determined. The dynamic responses of the tree structuree against sinusoidal wave motions were computed by modeling the tree into a lumped mass system. The temporal variations and spatial distributions of the horizontal displacement and bending stress of the trunk and branch elements were analyzed. Sensibility analyses were conducted by changing the imput parameters such as incident wave height, period and loading weight due to the leaves in the crown part. The obtained results on the maximum bending stresses can be utilized for the damage analysis of the tsunami barrier forests under tsunami attack conditions.

View full abstract

The shear stress acting on the bed around vertical circular cylinders and artificial seaweeds installed in a wave flume with multiple rows are measured by using a shear stress sensor. The sand movement and local scour around these plant models are also observed. The close agreement between the time variation of shear stress measured by the shear sensor and the estimated values from the theoretical values of boundary layer equation in harmonic flow with laminar flow are obtained in the case of regular wave with smooth bed. The shear stress on the smooth bed with vertical circular cylinders increase compare to the shear stress on the bed without circular cylinders. The sand in side of these plant models move mainly in the direction of shoreline. These phenomena may be due to the disappearance of ripple on the sand bed with circular cylinders.

View full abstract

This study conducted field observations in terms of beach surface temperature ground cover ratio of beach grass water content and grain size of beach sand in August 2003 at an open ocean beach in Japan in order to investigate the effect of the ground cover on thermal environment at beach. The temperatures of sandy area and grass area had strong proportional relationships with solar radiation. In addition the proportional coefficient of the grass area was one-tenth of that of the sandy area indicating that beach grass was effective in moderating the thermal environment in summer. Clear effects of the water content on the thermal environment could not be observed. These results obtained from high temporospatial resolution data will contribute to beach management.

View full abstract

Based on in situ primary production data in Kashima-nada, parameters in the photosynthesis formula of the ecosystem model were changed. As a result, a coefficient of determination (R2) between the measurements and the calculation value improved in 0.86 from 0.51. We calculated with a new parameter and considered a characteristic of the spatial and temporal variation of primary productivity around Kashima-nada. Repeatability of the seasonal variation of concentration of phytoplankton and nutrients improved especially on the sea surface. It is necessary to correct grazing by the zooplankton and boundary condition of nutrients to give calculation accuracy more.

View full abstract

This paper discusses about simulation methods for behavior of swimming Scallop larva. Diverse aquatic organisms exist as a larva under the water after birth. The larva moves and spreads according to flow condition, water temperature, salinity etc. Prediction of behavior of the larva is important and useful to manage sustainable fishery resources and fishing ground. Authors tried to simulate the behavior by means of two methods. One is concentration tracer method and the other is particle method. Applicability of both methods was examined based on comparison with field measurement data set in Lake Saroma. It was shown that particle method has high potential as a prediction method for behavior of the larva in Lake Saroma.

View full abstract

Benthos such as Amphipoda living in coastal sandy sediments are important food organisms for fish, but, factors controlling their distributions remain poorly understood. Here, we aim to solve this question by introducing our new approach encompassing ecology, geophysics and hydraulics / geotechnics. We performed sets of integrated observations / surveys and analyses concerning the in situ intertidal geoenvironments and the benthos distributions at three natural coasts. The results demonstrate that the waterfront suction governs the variety of the habitat environments, involving a range of the degree of saturation, stiffness and void state, and the manifestation of the peak and critical area of densities for the three dominant species are uniquely determined by the magnitudes of such suction which are found to be particular to species throughout the coasts. These findings will effectively contribute to the conservation and management of fishery resources at sandy coasts.

View full abstract

To evaluate the effect of artificial upwelling producing structure on lower tropic production hydrodynamics and lower-tropic ecosystem simulations were executed. To verify the reproducibility of the simulation results of the field observation were used. As a result the bottom layer flow acting on the structure and fluctuation of temperature induced by internal tide were reproduced. However the problem was left on the evaluation of mixed layer depth of the temperature. On lower-trophic ecosystem simulation POC Sinking fluxes were reproduced. Suggested by the simulation the area that primary production was increased by effect of the structure extended 30 km north-south direction and 10 km west-east direction. And the value of increase was estimated at 1.3 mgC/m²/day.

View full abstract

Sensitivity analysis for dominant factors of hypoxia was conducted using Benthic-Pelagic coupling model in Ariake Sea. It became clear that (1) Natural variation of tidal amplitude in open sea affects more than geographical features modification for the change of tidal current since 1977 (set as the case for analysis) in inner area. (2) Oxygen consumption changes influenced from the change in the amount of primary production which unavailable benthic activities. In addition, these analyses those made clear that the primary production variation depends on bivalve amounts and intensity of tidal current except river discharge change and meteorological variation from consideration. It was shown again that recovery of tidal current and benthic activity is important problem for reducing hypoxia.

View full abstract

We developed an ecosystem model for brackish lakes considering dynamics of suspended bacteria such as heterotrophs and nitrifier, and applied it to Hinuma Lake for its calibration and validation. The model predicted well seasonal water quality changes in 1998 and 2004 compared with the previous model in which the suspended bacteria were not incorporated as model components. In particular, the estimation of the biological reactions such as nitrification and denitrification was effective in the simulation of ammonia and nitrite concentration. Additionally, nitrogen balance in Hinuma Lake estimated from the simulation showed the reliability of the model structure.

View full abstract

The earlier Tokyo Bay before reclamation (tidal flat existing system) and the existing Tokyo Bay (present system) were simulated by ECOHYM, the ecological model representing benthic-pelagic ecosystem coupling, and were compared to investigate the tidal flat function on hypoxia and ecological chain from the lower to higher level trophic production. ECOHYM demonstrated that the tidal flat existing system decreased 50 % volume of hypoxia and increased 15% biomass of benthic fauna, treated as higher level living-organism in ECOHYM compared to the present system. In contrast, inhibition of nutrients load derived from rivers did not accelerate the ecological chain path from the lower to higher trophic level, although it was effective to decrease hypoxia and mortality of benthic fauna due to oxygen depletion. These results show that a bountiful ecosystem is not restored only by the inhibition of eutrophication but also by the recreation of tidal flats.

View full abstract

This study aims to build up the HSI model to estimate habitat suitability correctly for 7 kinds of benthic animals on a tidal flat in the Yoshino River. We used two or three kinds of physical quantity of median particle diameter, mud content and bed elevation as an environmental influence factor of the object benthos and built up 4 kinds of the HSI model. We selected the most accurate model among 4 models in the reproduction precision of the activity population every animal. The integrated prediction accuracy of the selected HSI models for 7 kinds of benthos is high with 86.5% from 71.5%. Furthermore, we utilized these HSI models, and the habitation prediction map of the benthos was created.

View full abstract

The estimating the settling velocity of suspended organic matter (SOM) under the effects of salinity is necessary for developing a pelagic-benthic coupled ecosystem model to evaluate the coastal environment, where SOM is deposited on the sea bottom. In this study, laboratory experiments were performed with several materials, such as bentonite and SOM by using a particle distribution analyzer in order to estimate the settling velocity of SOM. From the experiment results, it was found that salinity accelerated the flocculation of settling particles, especially, loose flocs formed when SOM was consisted low amount of organic matter. As the flocked particle size increased, the settling velocity of SOM decreased.

View full abstract

Numerical simulation of wind and sea-salt particle transport was performed using a Reynolds-averaged turbulence model. Spatial distributions of time-averaged airborne sea salt locally varied under the influence of complex terrains and ground surface roughness with decaying tendency according to the distance from shoreline. In comparison between observational value of deposited sea-salt and numerical value of airborne sea-salt, they showed significant correlation with each other except for points very close to shoreline, suggesting that this simulation technique has a capability to appropriately estimate the spatial distribution of deposited sea-salt and airborne sea-salt, though there is still room for improvement in inlet boundary conditions on the sea for better estimation of sea salt near shoreline.

View full abstract

To estimate dry and wet deposition flux of anthropogenic nutrient transported from the urban area to the sea surface, we observed behaviors of PM2.5, which is particulate matter smaller than about 2.5 micrometer generated from car, truck and bus in Hiroshima city. We have also developed a numerical simulation model that consists of atmospheric and chemical reaction model. We investigated characteristic of nitrate and NO₃^- in time and space and then estimated the dry and wet deposition flux. The nitrate deposition flux generated from vehicle transportation in the urban area affects the ocean environment at nearshore zone and its concentration can be computed by the model.

View full abstract

To examine temporal variations of floating-litter transport and evaluate annual flux into Tokyo Bay, we did field measurements of floating-litter transport in a large river (Edogawa River) under flooding conditions. We also did a laboratory experiment to investigate the effect of the litter on the dissolved oxygen (DO) consumption of the water column. The results indicate that the peak of the floating-litter transport in flooding events are significantly different with that of the discharge, and show an appreciable dependence of the temporal variations of floating-litter transport on the flooding conditions. The annual volume of floating litters flowing into Tokyo Bay under large-scale flooding condition is an order of 10⁵ [m³], and thus the DO consumption of floating litter in this condition may be almost the same as those of bottom sediments and river water.

View full abstract

To accurately evaluate pollutant load in high-flow conditions in rivers without measured water quality, we present a new rating curve for pollutant loads (L=aQ^b , b: coefficient) in which non-dimensional discharge Q and pollutant load L are introduced. The present method adopts correlation between the coefficient b in the rating curve and land use in watersheds. We apply the present method to evaluate the coefficient b and pollutant loads in several types of rivers. The results indicate that the pollutant load evaluated by the present method are acceptable agreements with observed data, showing the fundamental performance of the present method to evaluate pollutant load in flooding conditions in rivers without measured data of water quality.

View full abstract

The movement of sand and gravel placed on the tidal mud flat under the wave action was investigated on Nakatsu tidal flat in Oita Prefecture. On December 12, 2009 sand was newly deposited in front of the seawall where there was no sandy beach in the past. The newly formed beach is composed of coarse sand different from mud composed of the tidal flat. Such sand was suddenly transported from offshore and deposited. The cause was investigated through the field observations and numerical analysis using the contour-line-change model.

View full abstract

The final goal of this study is to develop a floating device for improvement of the sea environment in a semi-enclosed bay, which is driven by renewable wave energy. As a first step of such a study, under the assumption that the floating device was fixed to the water surface, various cross sections of the floating device were examined to find out an effective cross section for vertical mixing of sea water in comparatively deep sea. The major driving force of a device for vertical mixing of sea water is the piston mode wave motions in the water chamber located at the center of the body. Additional functions of the device, such as dissipations of reflected and transmitted waves were also examined. It was found out that the asymmetry cross section with a horizontal connecting channel only in offshore side to a vertical water chamber was most effective.

View full abstract

This study mainly deals with characteristics of hydrodynamic forces on upwelling structures constructed on the sea floor with comparatively deep depth, say about 200m. Two different configurations of upwelling structures, typically a vertical plate model and a V-shaped plate model in the horizontal plane, were used as a practical model. The numerical analysis based upon CFD was applied to examine the effectiveness of upwelling structures and fluid forces in a quasi-steady flow such as a tidal current. Experimental verifications for such a numerical study were also carried out. The importance of wave actions on the upwelling structure was further examined theoretically for the stability analysis and structural design.

View full abstract

To understand oxygen consumption characteristics of sediment for the case of oxygen supply to the bottom of sea under the hypoxic condition, we carried out a laboratory experiment by using sediment and artificial-seawater. It is found that the oxygen consumption pattern of sediment is changing while sediment consumes oxygen. Immediately after oxygen supplying, dissolved oxygen of seawater was consumed by the chemical reaction in the sediment. And then dissolved oxygen consumed by the biological reaction.

View full abstract

The Amagasaki Canal where is an enclosed waters have been polluted and occurred eutrophication and hypoxic condition chronically. According to restore water environment in the canal, design of new restoration plant and substantiative experiment are preceded by the Amagasaki Sea Blue Project. In this study, long-term field experiment of water quality improvement technique using algae was examined. Water of sea bottom drawn from the canal and flow into the experimental small channel. This study focused on reduction of nutrients concentration and aeration with the photosynthesis by algas which was luxurianced naturally. As a result, it is found that the technique was very effective in daytime and summer in particular and disposal of exuberant algae will be required for isolation from material circulation in the canal.

View full abstract

Relationships between environmental factors (such as the ground level and sediment qualities) and growth conditions of Zostera Japonica were investigated by a growth experiment using a tidal exchange tank. Z. japonica grew up well in the submergence condition which the ground level was below DL: 0m and max temperature was under 29℃. On the mad-sand mixure sediment, the Z. japonica grew up better than on the pure sand and the pure mad sediment. The root branch and the leaf growth were promoted by nutrients in pore water (above 0.15mg-N/L in DIN and 0.015mg-P/L : DIP). Therefore it is clear that the ground levels and the sediment qualities were important environmental factors for the growth of Z. japonica

View full abstract

Recently, the various environmental problems such as red tide, anoxic water and etc. occurred in Ariake Bay. Tidal flats in Ariake Bay were reclaimed from pre-Edo era to the post-WWII food shortage period for the main purpose of increasing farmland. In the process, the revetments were constructed to protect farmland existing around the supratidal zone (shoreline). In this study, the field demonstration of rehabilitation technologies for Ariake Bay "recovery of shoreline" was done in Kumamoto Port. As the result, the number of benthos species increased more than those before the shoreline construction.

View full abstract

This study aims to investigate experimentally the effects of an electrochemical method on growth promotion and settlement of corals. Naturally growing colonies of the pier in Taketomi Higashi port showed significant increase in density of corals corresponding with electricity of the cathodic protection. To know the reason of these effects on settlement and growth promotion, field experiments and laboratory experiments were carried out. As a result, the settlement rate of electrochemically deposited bases was 5 times larger than that of ceramic bases. The growth rate of the treated nubbins was relatively high in the field and its effect depended on species. The laboratory experiment results indicated that positive effects on the growth of corals by the feeble electric current densities in the range from 50mA/m² to 100mA/m².

View full abstract

A lot of artificial coasts and the water front parks were created in Japan in order to improve the water amenity recent years. Contrary to expectation, some were polluted due to the self-pollution effects. The purpose of this study is to examine the self-pollution effects and its countermeasure to depress them in the artificial sea pond. One of them was control the inflow and the residence time of sea water in the pond. When a water level were raised more than now by 35 cm, the average maximum water temperature was provisionally calculated falls by 0.8 degrees. In addition, we could propose to change the bottom material of pond made of the concrete to the mud such as in a tidal flat where various living things lived and many materials circulated.

View full abstract

In the sediment of the estuary of the Chikugo River where inflow load quantity to Ariake Sea was bigger ,the carbohydrate was measured. The carbohydrate in the sediment surface of the estuary of the Chikugo River quantity was around 10 times higher than Ariake Sea sediment. Carbohydrate quantity to the time of edd tide is increased and to the times of a high-tide was decrease, it based on dissolubility carbohydrate caused by an adhesion alga. The dissolubility carbohydrates have chesion effect, and stabilization of sediment increased.

View full abstract

The influence of global climate change due to green house effects on the earth environment will require impact assessment, mitigation and adaptation strategies for the future of our society. This study projects future extreme ocean wave climate in comparison with present wave climate based on the atmospheric general circulation model and global wave model. The extreme sea surface winds and waves are analyzed based on extreme value methods in detail. There is a clear regional dependence of extreme winds and wave heights changes from present to future climates. The extreme wave heights of future climate would be increased significantly in tropical cyclone areas.

View full abstract

Tropical cyclone "Gavin" caused extremely high wave situation in Funafuti atoll, Tuvalu on March 1997. Although the extremely high waves due to tropical cyclones caused large morphological changes on atoll islands, the detail of the waves under tropical cyclones are not fully understood, because such strong tropical cyclones attack atoll islands once in a few decades. In this study, the numerical simulation of winds and waves under the tropical cyclone "Gavin" were carried out. The simulated results showed that the lagoonal significant wave height increased twice as high as the mean wave height in March. In the tropical cyclone situation, the place of passage and effective fetch are important for the lagoonal wave condition.

View full abstract

A radius of maximum cyclospheric wind speed is necessary to estimate a wind field by an empirical typhoon model for storm surge and wave simulations. In the present study, a stochastic typhoon model was established which has high reproducibility for mean distribution of passage number and central pressure of typhoons in the northwest Pacific. The relationship between radius of maximum cyclospheric wind speed and central atmospheric pressure was analyzed and parameterized to represent the probability distribution. Then, two different methods to project future typhoons were examined to apply for stochastic typhoon model under climate change scenario. Finally, the stochastic typhoon model which employs the presumed future typhoon tracks as input data was applied to evaluate climate change impact on typhoon characteristics.

View full abstract

In this study, the sensitivity experiments on typhoon intensity using an axisymmetric typhoon model developed by Yoshino et al. (2009) are performed in order to improve the accuracy of typhoon intensity predictions. The model enables us to predict the typhoon intensity change with low cost and high accuracy, owing to the use of a high-resolution axisymmetric solver. A number of sensitivity experiments indicate that the changes of typhoon's moving speed and vertical wind shear have a significant influence on the typhoon intensity change. It is found that the modification of the axisymmetric typhoon model incorporating realistic values for these sensitive parameters allows for reducing the forecast error of all typhoons in the 1999 Pacific typhoon season.

View full abstract