A float-type evacuation shelter has ever been proposed as one of urgent evacuation facilities by one of the authors. In this study, a new shelter covered by a sphere shell was proposed in order to control rotation of evacuation space for refugee. A series of hydraulic experiment was carried out to understand motion of the outer spherical shell and inner shelter. The outer shell had been kept rotating immediately after tsunami attack. In contrast, the inner shelter rotated once, but reverted back to the initial condition. The possibility of control of rotation velocity of the inner shelter by the weight was implied.

抄録全体を表示

The offshore harbor refugee is one of the most important topics in harbor planning and operation. Numerical simulations have been improved, however, they do not consider dynamic chain forces and wave diffraction in coastal area. The influence of dynamic chain forces is compared with the static catenary method. Ship motions become irregular, and the chain tension is much larger. Anchored ship motions are reproduced by considering the dynamic chain analysis and wave diffraction due to the Boussinesq Equations. New simulation method can improve the accuracy against our previous models. The effectiveness of two anchoring is verified. Simulated results show that the two anchoring is not effective in heavy seas at all. It is necessary to reconsider the current definition of offshore harbor refuge as the new stage of port planning.

抄録全体を表示

All large waves in a service time lead to slide of breakwaters should be considered in the probability design method based on allowable sliding displacement. Previous studies assumed that the sliding failure is caused by annual maximum waves obtained from a given extreme value distribution. However, the second or third maximum wave comparable to the annual maximum can cause the sliding failure of breakwaters. This study evaluates the sliding stability of breakwaters considering several storm events in one year as well as the difference of offshore wave's extreme distributions. It was found that depending on the tail length parameter and extreme value distributions, the expected sliding distances are different and that previous methods estimating for sliding distance underestimate the expected sliding distance in some cases.

抄録全体を表示

In order to examine the stability of caisson breakwater against Tsunami which flow over the top of caisson, wave flume experiments and numerical calculations were carried out. As a result of experiments, it is shown that the water surface elevation observed behind the caisson breakwater reached the maximum (or minimum) value earlier than that observed in front of the caisson did and this may decrease the stability of the caisson. As for numerical calculations, the water particle velocity which flow over the top of caisson is very large and large scale turbulence was computed behind the caisson. This large velocity and the turbulence may cause the caisson overturning, which was observed in the experiments.

抄録全体を表示

Recently, CFD and FEM analysis are being applied to design and disaster measures of port and harbor structures, and various reports have been performed so far. However, there are not many techniques for simulating accurancy good to the iteraction between wavefields and deformation and fracture of structures. So, we improved the system in the past by Arikawa(2009), and developed as a new Fluid-Structure coupled system, CADMAS-SURF/3D--STR3D, which can treat the large scale model and large scale deformation. And we verified the validity of this developed system, comparing with the water tank test in the past.

抄録全体を表示

Evaluation of the amount of the deformation is necessary for the performance-based design of caisson type composite breakwaters. However, the evaluation method of the deformation except for the sliding failure mode has not been established yet. Authors showed that the deformation of breakwaters is not as simple as mere sliding but is accompanied by the deformation in the rubble mound by using a past hydraulic model experiment result. In this study, authors discussed deformation characteristic of breakwater from the viewpoint of the penetration angle of the edge of caisson into the rubble mound and proposed an estimation equation of the penetration angle.

抄録全体を表示

This study discusses the target safety level of breakwaters against wave force in view of minimizing the life cycle cost. We considered both damage recovery cost and economic loss cost in the calculation of life cycle cost. We found that target safety level changes according to the condition such as extreme value distribution of waves and ratio of economic loss cost to damage recovery cost. Target safety levels of composite breakwaters were found to be different from those of breakwaters covered with wave dissipating blocks. In addition, target safety levels corresponding to the minimum life cycle cost were found to be different from the allowable safety levels by the technical standards.

抄録全体を表示

Kainan region of Wakayama port is predicted with a high probability to be attacked and inundated by huge tsunami. To prevent the tsunami disaster a set of special movable breakwaters, which are called vertically telescopic breakwater (VTB), is planned to construct at the mouth of Kainan Port. The set of the piles consist of a movable upper pile and a fixed lower one. The upper pile is raised by the buoyancy of air supplied into the upper pile through a pipe, as soon as a tsunami warning is issued. After the tsunami calms down, the air is discharged by opening of a valve. The present paper describes a performance based design of VTB for the protection of Kainan region from tsunami. In the design the performance requirements for VTB are defined and the evaluation procedures of the required performances are proposed.

抄録全体を表示

Stability of armor units of rubble mound breakwater against tsunamis was investigated using armor units of which mass ranges from 14g to 500g. Water depth and velocity were measured on the rubble mound breakwater to discuss the applicability of an experimental formula. The water depth and velocity were also estimated applying 2D numerical simulation for complementing velocities which were not obtained by the experiments. Soliton fissions generated in short period tsunamis were also simulated. The present work has revealed that the mass of armor units is underestimated if the Isbash's formula is used for the rubble mound breakwater.

抄録全体を表示

In Japan, detached breakwaters made with wave dissipating concrete blocks such as Tetrapods have been widely applied. On March, 11^th, 2011 the huge, devastating tsunami generated by The 2011 off the Pacific coast of Tohoku Earthquake attacked and damaged the east coast area of Japan. In our study, hydraulic model tests have been systematically and carefully carried out using solitary tsunami waves to evaluate the stability of concrete blocks following the our previous study on the effect of detached breakwaters from the viewpoint of reducing run-up and wave pressure onto seawalls behind the detached breakwaters.

抄録全体を表示

A composite type breakwater with back-filling was applied to improve the stability acting on wave forces. In this paper, 2-dimensional wave tank tests were carried out to reveal the effects of the interaction wave forces and back-filling reaction forces. The back-filling reaction forces acting on the breakwater were measured by 2-dimensional load cell. The composite type breakwater with back-filling is stability more than without back-filling structures. And it is confirmed that the existing design method is safety side evaluation more than the experimental results.

抄録全体を表示

This study aims to develop an accurate placement method of fish nursery blocks utilizing free fall in the deep sea area. Falling behavior of concrete blocks in water was investigated by the hydraulic model tests and numerical simulations. As a result, a new nursery block shape which falls through water with highly stable behavior was developed. The validity of the numerical simulation method was confirmed by model tests. In addition, an quick estimable system on the placement position and the probability distribution on the sea bottom was also developed. In the system, the average placement position is calculated from hydrodynamic force calculations based on the hydrodynamic force coefficients. The probability distribution of the placement positions is predicted by applying Markov chain theory.

抄録全体を表示

This study aims to investigate the characteristics of wave force on the seawall with a large-scale artificial reef, in Shimane Nuclear Power Plant facing to the Sea of Japan. Field observations were carried out to measure the wave field and the wave pressure on the seawall. From the comparison between field observations and numerical analysis by CADMAS-SURF/3D which is a three-dimensional numerical wave tank model, we clarified that the nonlinearity of the primary waves, wave direction, and reflection by the seawall cause the increase of the amplitude of the long period waves. As a result we confirmed that the wave force on the seawall increases in proportion to the amplitude of the long period waves.

抄録全体を表示

An evaluation method of incipient motion on armor block for submerged breakwater is proposed. The method is based on a wave induced flow field around the submerged breakwater, which is calculated by a numerical wave flume CADMAS-SURF (Isobe et. al., 1999), and successive wave force calculation based on the Morison equation. Trial computation and comparison with experimental results demonstrate the validity and usefulness of the proposed method.

抄録全体を表示

Level 2 performance based design, which considers the probability of design values as normal or lognormal distribution, is introduced for coastal pumping stations. Considering inundation risk, the outer forces are assumed to be the increase of water levels in drainage canals caused by inflow, and counter forces are assumed to be the decrease of water levels in drainage canals caused by pumping discharge and drainage gate discharge. Design rainfall is modeled as lognormal distribution based on data from the Saga Meteorological station. Design tide levels are modeled as the sum of residuals of high tides caused by typhoons and astronomic tides at Oura. Based on a Monte Caro simulation for 100,000 years, the maximum water level data in drainage canals are calculated to evaluate performance.

抄録全体を表示

Recently, the use of sandbags made of a fiber-containing material has been examined for coastal protection. When the bag stuff worker is applied on an actual site, it is necessary to check the tension that acts on the bag material. In the present study, the tension acting on the sandbag was determined by performing a large-scale experiment. Moreover, the tension that acted on the bag material at that time was checked in reproducing the deformed state of by waves with the real-size model.

抄録全体を表示

Recently, an increase in the load from river basin and a food scatter of aquaculture causes eutrophication in the Imari Bay. Therefore, red tides have been generated. In order to decrease the red tide in the Imari Bay, we have clarified the characteristics of flow structure and water quality by means of water quality predicting model, taking account of river loads. As a consequence, it is clear that the main reason of strong red tide is the river loads form Sisa River. The river loads flow toward the south-east area of Takashima Island, meeting the warm water from the Matsuura thermal power station. And red tide bloomed enormously in 1999.

抄録全体を表示

"Aoshio" (the anoxic blue-green turbid water) was first observed in Isahaya Bay, Ariake Sea in August 15, 2008. Field data analysis and numerical experiments were made to clarify the generation mechanism of this "Aoshio" in Isahaya Bay. The field observations showed that the occurrence of "Aoshio" was associated with three characteristic phenomena, the intrusion of high density water (HDW) into the lower layer at neap tide just before the occurrence of "Aoshio", rapid decrease of dissolved oxygen(DO) concentration, leading to the formation of anoxic water during the HDW intrusion and transportation of this anoxic water to the head of Isahaya bay due to south-west wind-induced current, followed by the vertical mixing at around spring tide. Numerical experiments could reproduce these phenomena with high accuracy and the generation mechanism was confirmed by the numerical experiments.

抄録全体を表示

Open-ocean water intrusions from the Kuroshio surface (and/or intermediate) layer are considerable processes for the ecosystem of the semi-enclosed coastal sea such as the Seto Inland Sea. To reproduce the ecosystem in the Seto Inland Sea, a numerical ocean model is constructed by using daily reanalysis data demonstrating the Kuroshio path of the open ocean. The model results are verified quantitatively and examined the ocean water intrusion focusing cold water intrusion into the bottom layer of the Bungo Channel, and warm water intrusion in the surface layer of the channel, called kyucho. Modeled temperature explains the cold water intrusion into the bottom layer of the channel, and cannot demonstrate kyucho because of the lack of disturbance derived the Kuroshio frontal eddies in the reanalysis data.

抄録全体を表示

The effect of the salinity and organic mattter, such as Extraceller Polymeric Substances on the settlement of the suspended sediment and erosion of the estuarine sediment was studied. The surface sediments were sampled at the tidal river of the Chikugo River where the turbidity maximum is observed to use flocculation and erosion experiments. The results of the experiments showed that "concentration-based" settling velocity of the suspended mud increaces with increases of salinity. Suspended mud with EPS has much higher settling velocity comparing with the EPS removed sediment. On the other hand, "flux based " settling velocities of each sediments were almost same regardless of whether EPS was removed or not. Erosion thresholds of the sediments whose EPS were removed had lower than those of raw sediments

抄録全体を表示

We monitored temporal variations of a bottom sediment quality and benthic species diversity based on sediment sampling and analysis around the Tama river mouth in the Tokyo Bay. The monitoring started in 2006 and we focused on the impact of the extensive flood event in September 2007 on the benthic environment. As a result, the diversity and biomass of the benthic species were increased after the flood especially in the off shore of the river mouth. The re-colonization of the benthic biota is considered to be related with the favorable change in the sedimentary environment for the species with disappearance of fluff layer on the bottom surface by the flood event.

抄録全体を表示

The specific objective of this research is to investigate the characteristics of temperature changes between sea water and the covered material on the sea bottom, aiming to delineate the formation of thermal gradient due to the construction of large pore layer on the sea bottom. Field observations of water quality were conducted consecutively, and the formation of thermal gradient and the diffusivity coefficient were investigated based on the observation data. It is understood that the diffusivity coefficient in the large pore layer is smaller than that in the bottom sediment, resulting in the formation of a strong stratification. The large pore layer plays a major role in suppressing the increase in temperature of the bottom sediment.

抄録全体を表示

An unstable density field is formed near the bottom of Kaita Bay. It is predicted that the unstable density field is kept by density increment from suspended organic mud. In order to understand the property and behavior of suspended organic mud, relationship among of settling time, diameter and composition was investigated. Furthermore, density increment from suspended organic mud is confirmed. As a result, it is cleared that property of slowly suspended organic mud is small diameter and low C/N ratio. Additionally, density increment of suspended organic mud is bigger than that of soil particle.

抄録全体を表示

In Osaka Bay, water pollution phenomena such as red tide and blue tide still occur frequently, in spite of the efforts to improve water qualities for years. To make a decision about effective environmental measures in the bay, it is necessary to clarify the budget and cycle of nutrients in the waters. In this study, focusing on the water mass intruding from the outer ocean, a cluster analysis using salinity, nutrient concentrations, and stable isotope ratio δ¹⁸O and δD is conducted. The cluster analysis divides the coastal sea waters in and around Osaka Bay into six groups, including the clusters related to Kuroshio surface water and sub-surface ocean water, and the results show that the sub-surface ocean water had intruded into the Kii Channel due to off-shore migration of the Kuroshio Current in spring 2009.

抄録全体を表示

Coccolithophores are important microorganism for the carbon and sulfur cycles. Coccolithophores bloom was found on 3 October 2007 in Suruga Bay. The seasonal appearance of coccolithophores and the relationship between nutrients are as follows.1. Coccolithophores generally increased in spring and showed the maximum in May. In spring they distributed more offshore surfaces than coastal area. The whole cell density decreased in summer and became the peak in October. 2. The dominant species was Emiliania huxleyi. 3. Increase of coccolithophores at the forehead of stratification appeared after the bloom of small diatoms. As for the nutrients, phosphate and silicate were less than the half of saturation constant of diatoms, while nitrate still remained, of which concentration sufficient for coccolithophores to increase.

抄録全体を表示

In recent years, some of researchers have reported that most of nutrients in Suo nada are derived from open ocean through the Bungo Channel and Iyo nada. If these nutrients flow into euphotic zone of Suo nada, they can provide primary production and play an important role in Suo nada. We investigated pathway from Iyo nada to Suo nada by using observation data such as temperature, salinity, density and nutrients. As the result, we confirm existence of inflow from Iyo nada at euphotic zone in Suo nada. However, it is presented that less of contribution to primary production in Suo nada because of low nutrients in Iyo nada.

抄録全体を表示

Under water micro video scope was developed to measure floc settling velocity and applied to the suspended sediment floc in the Chikugo River estuary. The effective densities of the flocs were measured successfully. The floc density distribution function was proposed from the floc settling speed and their diameters. The floc density distribution function varied with tide. In ebb tide, floc densites were smaller than in flood tide. This fact shows that the flocs in flood tide mainly consists of the mud which was suspended from the river bed. Mass settling flux was also calculated. When suspended sediment contains algae or algal residuals, the settling velocity showed lower value. On the other hand, containing high concentration of extracellular polymeric substances (EPS) made settlement velocity high.

抄録全体を表示

To clarify change and actual condition of inflow load and sea environment in Osaka Bay from a not only quantitative but also qualitative point of view, loading amounts of COD, phosphorus, and nitrogen from 1980 to 2005 were estimated by collecting and analyzing statistical data about rivers, coastal waters, sewerage systems and so on. As a result, it was revealed that the plan outlined for reducing total pollution loads and the construction of sewerage system for years have shifted a nutrient balance of the inflow load and brought about changes in water quality structure and ecosystem in the bay. Moreover, analysis results indicated that nutrient loads caused by flood which people couldn't control had a significant impact on an annual total load compared with inflow loads in the ordinary condition.

抄録全体を表示

The environmental characteristics in seabed sediment behind the north and south drain gates of Isahaya Bay were investigated by sampling the undisturbed sediment cores. The vertical distributions of TOC, DO, AVS, NH₄-N, NO₃-N and PO₄-P were obtained. The material circulations in the sediment at two sites were analyzed by using a sediment model. The model parameters were adjusted so that the analytical results agree well with the observed ones. The model analysis revealed that the fluxes of organic material and oxygen consumption to the seabed surface at St.2 were two times larger than those at St.1, respectively. These differences at St.1 and St.2 may be attributed to the current in Isahaya Bay.

抄録全体を表示

Countermeasures against the formation of oxygen-depleted water in the bottom layer near head of the Ariake bay were studied using the ecosystem model developed by authors (2010). Three options of the countermeasures were chosen to satisfy the three conditions: effectiveness, feasibility and capability of numerical simulations. The first option is a reduction of load from the land, the second option is increase in Sarubow which is a bivalves live in the tidal flat near the head of the bay and the third option is increase in Oyster beds. The results of numerical simulations showed the effectiveness of each option quantitatively. The numerical experiments under some virtual conditions were also conducted to understand the problem. The numerical results presented some useful indications to solve the problem.

抄録全体を表示

Nutrient distribution and its relationship with salinity, turbidity, and the presence of phytoplankton in the highly turbid Chikugo river estuary were investigated in the early spring of 2010 by using multiple regression analysis. Water samples were collected from the surface and the bottom of the estuary at eight stations extending over twelve hours during two tidal periods. The relationship between the salinity and the nutrients during the spring tide was different from that observed during the neap tide. The dominating factors influencing the variation in the dissolved nutrient concentrations were both the salinity and the suspended sediment concentration. It is suggested that dissolved nutrients were supplied from the pore water of the sediment and that they were affected by the dilution with the seawater.

抄録全体を表示

Possible methods for reducing blooms of blue-green algae in Sagami Dam, Kanagawa, Japan, by controlling hydro power discharge were considered on the basis of field measurements and numerical experiments. Field data for currents and water quality were obtained and analyzed as well as time series of temperature. The measured hydrodynamic fields were successfully reproduced by numerical computation using MIKE by DHI. Using a developed simple water quality model, we performed numerical experiments controlling the hydro power discharge and found that a change of the discharge layer from the whole to the surface layer is considered to be effective for reducing booms of blue-green algae in the dam due to enhancement of surface currents toward the outlet and reduction in the surface temperature.

抄録全体を表示

Measurement technique of CO₂ for coastal seas is developed and applied to elucidate CO₂ dynamics in the coastal regions, where the photosynthetic rate is far larger than that in the open sea and the short-term change is significant. Continuous measurements of salinity, pH and DO were conducted at three stations in Osaka Bay. The values of CO₂ related terms were calculated using a classical method that uses pH and total alkalinity. Dissolved inorganic carbon (DIC) and DO fluctuated with high correlation (R² = 0.97). This suggests that CO₂ system can be measured by this method in coastal regions. DO and pCO₂ (CO₂ partial pressure) records in the eastern Osaka Bay, where primary production is significant, indicated prominent diurnal variations which correspond to diurnal irradiation variations. In contrast, magnitudes of DO and pCO₂ variations were smaller in a well mixed reason in the western Osaka Bay.

抄録全体を表示

Yatsushiro Bay is a typical closed bay on the west of the Kyushu Island, this sea area where a vast tidal flat develops. Recently, various environmental degradations are reported occur in Yatsushiro Bay, as red tidal and anoxic water. In this study, we tried the time series analysis of characteristic of the sediment, aim at the sea area environmental change characteristic in Yatsushiro Bay. As the result, the characteristic of the sediment in Yatsushiro Bay was classified into five patterns by the cluster analysis. The deterioration of the sediment being progressing in inner part of bay, near estuary and deep area in center part of bay became clear.

抄録全体を表示

It is demonstrated that duration of strong wind is one of the main factors which may enhance recovery from hypoxia in Tokyo Bay. Meteorological conditions are revealed to change, which may have caused more flood disaster, greater typhoon and so on in terms of climate change. Therefore, strong wind pattern is also expected to change and to have an effect on water quality in Tokyo Bay. This study thus aims to clarify the impact of meteorological change on the occurrence of and recovery from hypoxia by using Global Climate Model (GCM) outputs. As a result, it is suggested that the duration of strong wind decreases in the future.

抄録全体を表示

Importance of chemical oxygen consumption to the formation of hypoxia was cleared by measuring the DO concentration at the 0.2 m above the bottom, analyzing the hydrogen sulfide profiles in the sediment and some field experiments of the fraction of oxygen consumption (biochemical and chemical oxygen consumption) in the inner western area of Ariake Bay. Contribution rate of the chemical oxygen consumption to the total oxygen consumption at the 0.2 m above the sediment were 99.6% on 1 August, others were low (18 and 31 August). High chemical oxygen consumption before the hypoxic condition implicated that the chemical oxygen consumption has an important role to the generation of hypoxia in the inner western area of Ariake Bay.

抄録全体を表示

Constant monitoring system was established in Osaka Bay in April of 2010. Seven of 13 stations can monitor water quality, but are located near a northeast coastline of the bay. The spatial resolution of the monitoring water quality is not sufficient in broad eastern part of the bay where hypoxia and excess growth of phytoplankton occurs. In the present study, the obtained data are verified by field survey with a boat and used to clarify a behavior of hypoxic water. The data unveils that vertical mixing occurs in the innermost area during 24 hours of a southerly strong wind, resulting in the hypoxic water disappears. External drift kriging with the numerically simulated results by three-dimensional water quality model ROMS (Regional Ocean Modeling System) is tested and improve the spatial interpolation.

抄録全体を表示

Changes in concentrations of organic substances of the sediment and nutrient salts in the pore water of the riverbed were examined at a tidal area of the mouth of the eutrophic Yamato River in 2009-2010. TOC and TN contents of the sediment, together with NH₄-N and NO₂+NO₃-N concentrations in the pore water drastically changed depending on time, month and station. Production rate of NH₄-N in the pore water of the Yamato River was ca.10-100 times higher than that of laboratory experiments. These results suggest the importance of tidal change and wave in evaluating dynamics of organic substances and nutrients at the tidal area of the mouth of a river.

抄録全体を表示

It is important to understand physical conditions associated with the wave and the current in order to enhance settlement of the clam Ruditapes philippinarum on tidal flats. In this study, we unveiled the criterion for spatial distribution of the juvenile of the clam using frequency of sediment transport and Shields number based on the wave data. Consequently, we found that the clam could not inhabit the area where sediment was moved higher frequency more than 5 percent or no less than 0.2 of Shields number. Also, adequacy of these results was confirmed by the field survey.

抄録全体を表示

Eelgrass beds have important functions as water purification, spawning and nursery grounds for valuable marine resources. In recent several decades, eelgrass beds have been decreased by coastal reclamation. In order to suppress that phenomenon, various environments improvement technology has been tested. However, the long-term conservation of constructed eelgrass bed construction is difficult and there are not many success cases. It is considered that it is attributed to the surrounding condition in the objective marine area is not suitable for the optimum eelgrass habitat environment. In this study, we conducted the evaluation and analysis of eelgrass growth factors using the Self Organization Future Map (SOM) that kinds of neural network. Also, we verify the complicated relationship between the eelgrass growth factor and changes of marine environment. It would be the effective approach for the sea grass bed construction.

抄録全体を表示

The complex channel networks have dominant roles for flow, sediment and nutrient transport on salt marshes and tidal flats, and therefore provide rich habitat structures. This study discusses the fundamental geometric properties of tidal channel network by statistical analysis to their channel length and planimetric shapes. We employed channel networks which delineated from experimental and numerical result and also satellite image of real field. It is found that the probability density distribution of channel length can be described by a lognormal distribution, and network in experimental and real scale have similar properties for channel length. The results also indicate that the difference of tidal conditions change the characteristics of tidal channel network configuration.

抄録全体を表示

Tidal flat restoration was carried out from Apr. 2010 by opening the floodgates on the concrete dike, which was constructed for reclamation. The restoration site is about 2ha and located in the inner part of the bay (Ishibuchi in Shima city). Improvements were evaluated by monitoring sediment quality, benthic abundance and species diversity every season. Before the restoration, only 6 species of macro faunas, which lives in brackish water, were found. After the opening of the floodgate, the macro faunas was changed from brackish to saltwater and the number of species gradually increased. After 6 months, 22 kinds of juvenile fish, migratory macro faunas and small clams were found in the restoration tidal flat. At the same time, the COD and AVS in sediment decreased. in the restoration tidal flat.

抄録全体を表示

Temporal variability of carbon and nitrogen stable isotope ratios (δ¹³C and δ¹⁵N) in bivalves were investigated from May 2007 to February 2009 at two different stations in Tamagawa River estuary, Japan, together with chemical and isotopic compositions of potential food sources, such as suspended particulate matter and surface sediment. δ¹³C and δ¹⁵N in bivalves were enriched in the downstream station irrespective of the species. δ¹³C and δ¹⁵N of bivalves in both stations showed seasonal cycle, in which they were enriched in summer and depleted in winter. At both stations, remarkable decrease of clam δ¹³C was observed after a high flood discharge, indicating strong influence of terrestrial organic matter inflow. In conclusion, it is revealed that δ¹³C and δ¹⁵N in bivalves are useful markers to trace time-integrated information of estuarine environments.

抄録全体を表示

Mesoscale velocity fields of coastal region including the tidal flat area and the dispersion characteristic of floating larva of Tapes philippinarum were investigated based on the observational result with VHF radar and the numerical simulation results for the Nakatsu tidal flat and the surrounding coastal region in Suonada ( western part of the Seto Inland Sea). The results have shown that the characteristic tidal current fields are generated around the Nakatsu tidal flat by the topographical effects of river mouth, Nakatsu tidal flat. In addition, the simulation results of floating larva dispersion have revealed that the larva supply from Nakatsu tidal flat to the east fishery ground by the west wind in autumn, which is strongly influenced by the coastal topography, may play an important role for the dispersion processes of the floating larva.

抄録全体を表示

The aim of this study is to reveal the effects of flow rate and pore size on the general behavior of mud transport in sand beds, which is a useful knowledge in the restoration of aggravated tidal flats and the construction of man-mad sandy tidal flats. It is found that an increase in flow rate boosts the deposition amount of mud in sand beds. Moreover, it is noted that the deposition condition of mud in pores is mostly dependent on flow rate. Mud is easily deposit into pores in the case of a lower flow rate, and it deposits in a looser condition with a higher flow rate. Finally, it is suggested that the deposition distribution of mud corresponded with the pore distribution of sand bed, and mud deposits with a looser condition in larger pores.

抄録全体を表示

Emissions of CO₂ from tidal-flat sediments were measured using the chamber method to investigate the characteristic of organic matter degradation at the north pond of Osaka Nanko Bird sanctuary. Indoor experiments were also conducted to clarify the effect of changes of the groundwater level on the CO₂ emission by manipulating the water table level of the sediment. The amount of organic matter degradation varied seasonally and increased with increase of temperature and biomass of benthic organisms in summer. Emissions of CO₂ from the bottom sediment were highest when the water table level was lowest at low tide in a day. These results demonstrate that the amount of organic matter degradation varies daily or seasonally depending on temperature, groundwater level and biomass of organisms of the bottom sediment.

抄録全体を表示

The carbon captured by living organisms in oceans is stored in the form of sediments from mangroves, salt marshes and seagrasses. We evaluated the blue carbon sinks by gastropod Cerithidea cingulata in river mouth tidal flat. We determined oxygen consumption of C. cingulata in the air and water conditions. Oxygen consumption grew with increasing temperature and shell length in both conditions. Approximately 80% of the carbon biomass was an inorganic carbon from shell origin. We calculated that the amount of carbon source as respiration and dead was 26 kgC/year, sink as production, shell formed, shell buried was 40 kgC/year in this muddy tidal flat. These results indicated that C. cingulata plays a role for contribution to sink the blue carbon

抄録全体を表示

By utilizing our new approach in Ecological Geotechnics, we have recently constructed a burrowing performance chart which enables an interspecific comparison of the burrowing capabilities of benthic fauna in light of the associated geophysical environments in the field. Here, we performed sets of integrated observations / surveys and analyses concerning the in-situ intertidal geoenvironment and benthos distributions at various natural and artificial tidal flats located in Kumamoto, Chiba, Okinawa and Yamaguchi Prefectures in Japan. The benthic fauna analyzed involve five species of invertebrates that belonged to Arthropoda, Mollusca, and Annelida. The results demonstrate the validity and effectiveness of the burrowing performance chart in not only evaluating but also predicting the linkage between the benthos distributions and the ensuing geoenvironment in these tidal flats. Hence, this chart will effectively contribute to a new horizon of the performance-based geoenvironmental assessment, design and management of habitats with diverse ecological activity.

抄録全体を表示

To understand effects of river environment on water quality in mangrove estuary, distribution of physical (depth, salinity, DO and turbidity) and chemical parameters (NO₃-N, NO₂-N, NH₄-N, PO₄-P, TN, TP and SS) were investigated in two different mangrove rivers (Miyara and Fukido river) in Ishigaki island, Japan. Concentrations of NO₃-N were approximately 16 times higher in the Miyara river which is located near sugarcane fields and cowsheds than in the Fukido river, with intact mangrove forests. DIN/TN ratios in the Miyara river were high (>65%) throughout the tides, but ratios in the Fukido river increased at ebb tide and decreased at flood tide. These results suggest that compositional characteristics of nitrogen in the Fukido river change with tidal dynamics and it may affect coastal ecosystem from the aspects of nutrient source.

抄録全体を表示

Behaviors of organic sediment and groundwater in tidal flats in a bend of a tidal river were investigated by field experiments. The horizontal advection was reduced by the hydraulic resistance of mangroves, and sediment which has large C/N ratio repeats deposition and re-suspension near the mangroves. At the inside of the bend, since fresh fine organic mud deposited on the sandy bed 10 cm thick, the groundwater salinity in the sandy layer was hardly influenced by the tidal variation of stream water salinity. Low salinity water flows down at the inside bend and current velocity decreases at the outside bend due to mangroves and shallow water.

抄録全体を表示