Experimental tidal flats with peaks and trenches were constructed in a tidal flat mesocosm system (TFMS). The effects of changes in absolute elevation, i.e.. changes in datum level on the structure of the benthic communities and sediment matter were investigated. Further, planktonic larvae of the Japanese littleneck clam (Ruditapesphilippinarum) were added, and the relationship between larval settlement and the peaks and trenches was investigated. In terms of the structure of macrobenthic communities, the spatial distribution of the biomass of each feeding type corresponding to the areas of peaks and trenches was maintained, although the datum level was lowered from 0.3 m to 0 m. Macrobenthic biomass. as a whole, did not change with variations in the datum level. However, when the datum level was lowered, feeding type of macrobenthos altered from subsurface deposit-feeding types to suspension and surface deposit-feeding types. This may be due to the increase in flux of particulate organic matter, and the increase in the abundance of sedimentary organic matter and bacteria in the trenches. Moreover, it is thought that physical accumulation in trenches is also an important factor. The spatial distribution of mciobenthic biomass was similar to that observed in macrobenthos with variations in the datum level: however, the biomass as a whole decreased. The deviations of biomass of the sediment matter and bacteria at the areas of peaks and trenches increased when the datum level was lowered. Trenches exhibited the highest density of Japanese littleneck clams: this tendency was similar to that observed in suspension-surface deposit feeders, and may be attributable to physical accumulation. The juvenile density was loo large for these animals to have been initial settlers: thus, they were probably relocated individuals. It is thought that juveniles actively drifted in the TFMS.
The water exchange between a borrow pit and an ambient water is widely divergent, which is dependent on the aspect ratio of the borrow pit. and stability condition of water column. Large Eddy Simulation (LES) method was applied to examine this type of water exchange. In model experiments, various types of stratification and current velocity conditions were examined by using LES model for the water exchange between a borrow pit and an ambient water. We found an optimum Richardson numbers to start a water exchange between a borrow pit and an ambient water.
Aiming at understanding the flow velocity, temperature and salinity fields, a 3D time-dependent hydrodynamic model was applied to Hirota bay using the few monitoring data. The model was run to reproduce the time variation in water temperature, salinity and flow velocity during two periods, flood season from September to October 1991 and normal season from July to September 1992. The hourly-change regimes of the observed tidal elevation at the open boundary, river discharges, winds and meteorological parameters were incorporated into the forcing variables of the model. The model results agreed fairly well with the observed date except some minor discrepancies. It was found from the results that the flow field in the surface layer varied considerably yearto- year depending on the river discharge. The flow field in the autumn of 1991 was characterized by an offshore current system affected by flood river plume, and in the summer of 1992. it was very stagnant under dry and calm conditions. On the other hand, simulated vertical flow fields at the longitudinal cross section were consistent with two periods, despite the differences of current velocity. It was characterized by outflow in the surface layer, inflow in the middle layer and outflow in the bottom layer.
The Lake Sanaru is one of the representatives of coastal lagoon, and this system is well known as the most polluted aquatic
system in Japan. In order to understand the water pollution mechanism of this lake, we applied the physical-ecological coupled
model to this area. This study is still under model calibration stage. We changed the parameter values of potential growth rate of diatom, feeding pattern of carnivorous zooplankton. and mineralization rate of DOC. and examined the sensitivity of these parameters. These parameters were key factors in the model, and we could estimate appropriate order of these parameters from these calibration runs. By introducing optimum temperature for diatom growth, the succession between diatom and blue green algae can be reproduced well in the model. By reducing the mineralization rate of POM and DOM. the biomass of carnivorous zooplankton and inorganic nutrients concentrations are well reproduced in the model. Based on the calibration run. the biochemical fluxes in Lake Sanaru in terms of nitrogen and phosphorus were examined.
Previous observation revealed that dugong (Dugong clugon) often feeds at intertidai flats near Talibong Island where the seagrass beds are completely exposed in the air during low tide. We aimed to determine the reason why the intertidel seagrass beds are more important for dugong than other subtidal beds. In dry season, we collected seagrassses at intertidai feeding ground and other subtidal site and compared the biomass(dry wt). species composition and grazing efficiency of seagrass between two feeding grounds. We also compared the nutrients contents between the seagrasses at each seagrass bed in dry season. There were no significant differences of all comparisons between intertidai and subtidal seagrass beds in dry season. At the same time. Dugong ’s feeding sounds were recorded at the intertidai and subtidal bed. There was a significant bias in the distribution of average feeding sounds per 30 minutes at every 50 cm depths. According to the distribution, dugongs seemed to prefer to feed in the specific tide level zone. This study suggests that the tide level at feeding affected the feeding ground utilization by dugongs.
As a part of studies for the Amitori remains, we carried out recently the seismic and electrical explorations in Iriomote Island, southwestern Okinawa prefecture. Amitori village was finally abandoned in 1971. because of its imperfect infrastructures. At present, however, there only exists one institution, the Okinawa Regional Research Center of Tokai University. Archaeological explorations in the Amitori area have already been made several times and many relics of the past were dug out within a 1.5-2.0 m thick surface layer. This is the first attempt to apply geophysical (seismic refraction and electrical resistivity) methods to the Amitori area in order to make clear a detailed shallow structure down to the depths of 10m or so. We selected three main survey lines with the lengths of about 100-150 m. two of which locating within the central part of village and the other in a nearby rice field. The results obtained are summarized as follows;
(1)The most suitable seismic model of the underground structure in this area is composed of four layers. These are, the surface layer (sand), 2nd (sand stone), 3rd (mud stone), and 4th (sandy shale) layers, continuously. The distribution patterns of electrical resistivity are harmonized strongly with the seismic model. Moreover low resistivity zones may be inferred as to be connected with groundwater distribution.
(2)The thickness of surface layer is presumed as about 2.0 m uniformly within the whole area of Amitori village. In the
archaeological surveys most of the relics are found in the surface zone within 1.5-2.0 m thickness, consequently all relics being buried in the first layer.
(3)Generally it is difficult to discriminated directly on the location and, or shape of buried relics using simply the seismic on electrical method, but it must be easy to make clear on the form or boundary of surface layer as an object of archaeological surveys. Therefore the present results obtained by geophysical techniques may play an important role in the archaeological studies of Amitori remains. Iriomote Island. SW Okinawa.
This study compares the sensitivity of temperature variability in ice and snow cover layers and heat flux in ice layer to change in air temperature between 3 m thick Arctic sea ice with 40 cm thick snow cover and 40 cm thick Okhotsk sea - ice with 18 cm thick snow cover. In Arctic sea-ice, only the top 70 cm thick layer shows clear sensitivity and the lower layer below this level shows no marked sensitivity to fluctuation in air temperature, even when the air temperature showed as large as 17 t) of change in several days because the ice is covered with thick snow. On the contrary, in Okhotsk sea-ice which has only 18 cm thick snow cover, the temperature in both snow cover and ice layers is very sensitive to change in air temperature, even when 10 ℃ is reached in change in air temperature. The estimated heat flux in ice layer was almost constant at 8. 2 ± 1. 5 W/m^2 at any depth below the sensitive layer in the Arctic sea - ice, however, the heat flux through entire layer of the Okhotsk ice showed a wide range of 8. 7 ± 8. 3 W/m^2. It was noticed that the heat flux through thinner sea-ice with thinner snow cover like the Okhotsk sea-ice was more sensitive to the change in air temperature. The temperature in ice layer followed the change in air temperature with a few to some hours of delay.
A seasonal variation of phytoplankton community structure in Shimizu Port was estimated from photosynthetic pigment compositions based on a nonlinear optimization algorithm. Observations were carried out 20 times from February 2006 to February 2007 at 7 stations. 7 major pigments including chlorophyll-a were quantified by HPLC, and five dominant classes of alga were selected for the analysis based on microscopic observations. Obtained station-pigment data matrix Y for each observation date was decomposed to the product of an alga-pigments matrix A and a station-alga matrix X simultaneously by using a nonlinear optimization program equipped in Microsoft Excel Solver. Each element of matrix X was constrained to be non-negative, and each element of matrix A was limited within a minimum and a maximum values. A time series of matrices Xkand Ak(k = I, ・・・20) were obtained from the iterative calculation for 20 observation datasets. The resulted Akshowed a seasonal variation of the fucoxanthin/chlorophyll-a ratio contained in Bacillarvphyceae, which increased when their sizes increased. On the contrary, zeaxanthin/chlorophyll-a ratio contained in Cyanophyceae decreased when their population increased. The characteristics of the method applied to spatial datasets were also examined.
We have developed a bioaccumulation model to predict the levels of hazardous chemicals in a food chain of Tokyo Bay. The
model, called the AIST-Bioaccumulation Model for Conger myriaster in Tokyo Bay. has four compartments: phytoplankton.
zooplankton. small fish and the conger eel (Congermyriaster). which was set as the top predator in this food chain.
The chemical Coplaner Poly Chlorinated Biphenyl (Co-PCB) is a persistent organic pollutant that bioaccumulates in the natural environment and is highly toxic to humans. In this study, we modelled the accumulation of Co-PCB in Conger myriaster using the environmental concentrations of Co-PCB from existing data of 2004 collected in Tokyo Bay in 2004. and estimated the temporal variation in the concentration of Co-PCB in Conger myriaster over five years at a stationary field in Tokyo Bay. The Co-PCB concentrations in Congermyriaster predicted by the model were the same as the levels recorded in water samples collected in July 2008. This suggests that this model simulates bioaccumulation of this chemical with great accuracy.
We have developed an ecological risk assessment model and used it to estimate the ecological risk of specific harmful chemicals in seawater. We calculated the concentration of chemicals, such as TBT. in a high-resolution gradient of an estuary and with high accuracy using a database of the results from a 3-D hydrodynamic model and ecosystem model. Generally, the ecosystem risk assessment model has been used with a mainframe and a workstation. Further, only some researchers and experts were able to operate the model since they needed to set the many complex parameters. To make this model more user-friendly, we rewrote the program in C++ language so that it runs Windows® with a Graphical User Interface (GUI). The calculation domains were set as Tokyo Bay (AIST-RAMTB). Ise Bay (AIST-RAMIB) and Seto- Inland Sea (AIST-RAMSIS). These domains have the following functions: 1) allowing the manual setting of chemical loading fluxes from user-defined points such as, major rivers, commercial harbors, navigation routes, and the atmosphere. 2) calculating chemical concentrations in their dissolved and adsorbed phases in seawater. 3) setting the NOEC(No Observed Effect Concentration) and the UF(Uncertainty Factor) for user-defined biota in the estuary. 4) estimating the ecological risk to aquatic organisms. 5) plotting the calculation results as a horizontal distribution, vertical cross section, and a time-series graph, 6) storing the calculation data in the CSV format and images of the display data in WMF, BMP, and JPEG formats. This software is freely available to the public on the Advanced Industrial Science and Technology (AIST) website: http://www.aist-riss.jp/projects/RAM/. It is already widely used by over 230 groups at universities, technical colleges, institutes, local governments, and companies. These groups use the model toassess ecological risks in sea areas, and for environmental education. research, and policy-making.