Akira Shibata

Study on the fate of petroleum-derived polycyclic aromatic hydrocarbons (PAHs) and the effect of chemical dispersant using an enclosed ecosystem, mesocosm.

Polycyclic Aromatic Hydrocarbons (PAHs) are one of the components found in oil and are of interest because some are toxic. We studied the environmental fate of PAHs and the effects of chemical dispersants using experimental 500 l mesocosm tanks that mimic natural ecosystems. The tanks were filled with seawater spiked with the water-soluble fraction of heavy residual oil. Water samples and settling particles in the tanks were collected periodically and 38 PAH compounds were analyzed by gas chromatography-mass spectrometry (GC-MS). Low molecular weight (LMW) PAHs with less than three benzene rings disappeared rapidly, mostly within 2 days. On the other hand, high molecular weight (HMW) PAHs with more than four benzene rings remained in the water column for a longer time, up to 9 days. Also, significant portions (10-94%) of HMW PAHs settled to the bottom and were caught in the sediment trap. The addition of chemical dispersant accelerated dissolution and biodegradation of PAHs, especially HMW PAHs. The dispersant amplified the amounts of PAHs found in the water column. The amplification was the greater for the more hydrophobic PAHs, with an enrichment factor of up to six times. The increased PAHs resulting from dispersant use overwhelmed the normal degradation and, as a result, higher concentrations of PAHs were observed in water column throughout the experimental period. We conclude that the addition of the dispersant could increase the concentration of water column PAHs and thus increase the exposure and potential toxicity for organisms in the natural environment. By making more hydrocarbon material available to the water column, the application of dispersant reduced the settling of PAHs. For the tank with dispersant, only 6% of chrysene initially introduced was detected in the sediment trap whereas 70% was found in the trap in the tank without dispersant.

Study of the effect of water-soluble fractions of heavy-oil on coastal marine organisms using enclosed ecosystems, mesocosms

Mesocosm facilities composed of 4 experimental and 2 reservoir tanks (1.5 m in diameter, 3.0 m in depth and 5 tons in capacity) made of FRP plastics, were constructed in the concrete fish rearing pond in the Fisheries Laboratory, The University of Tokyo. The water-soluble fraction of Rank A heavy residual oil was formed by mixing 500 g of the oil with 10 l of seawater, which was introduced to the 5000 l-capacity tanks. Experimental Run 4 was conducted from May 31 to June 7, 2000. Oil concentrations in the tanks were 4.5 microg/l called LOW, and 13.5 microg/l, called HIGH tank. Bacterial growth rates very quickly accelerated in the HIGH tank just after the loading of oil which corresponded with a high increase of bacterial cells in the same tank after 2 days. Later, bacterial numbers in HIGH tank rapidly decreased, corresponding with the rapid increase of heterotrophic nano-flagellates and virus numbers on the same day. Sediment traps were deployed at the bottom of the experimental tanks, and were periodically retrieved. These samples were observed both under light microscope and epi-fluorescent microscope with UV-excitation. It was observed that the main components of the vertical flux were amorphous suspended matter, mostly originating from dead phytoplankton and living diatoms. It was further observed from the pictures that vertical transport of oil emulsions were probably conducted after adsorption to amorphous suspended matter and living diatoms, and were settling in the sediment traps at the bottom of the tanks. This means that the main force which drives the soluble fraction of oil into bottom sediment would be vertical flux of such amorphous suspended particles and phytoplankton. Further incubation of the samples revealed that the oil emulsions were degraded by the activity of autochtonous bacteria in the sediment in aerobic condition.

Scale-reconstructable Structure from Motion using refraction with a single camera

Three-dimensional (3D) measurement is an important means for robots to acquire information about their environment. Structure from Motion is one of these 3D measurement methods. The 3D reconstruction of objects in the environment can be obtained from pictures captured with single camera in Structure from Motion. Furthermore, the camera motion can be obtained simultaneously. Because of its simplicity, Structure from Motion has been implemented in various ways. However there is an essential problem in that the scale of the measured objects cannot be computed by Structure from Motion. In order to compute the absolute scale, other information is required. However this is difficult for robots in an unknown situation. In this paper, we propose a method that can reconstruct the absolute scale of objects using refraction. Refraction changes the light ray path between the objects and the camera. This method is implemented using only a refractive plate and single camera. The results of simulations show the effectiveness of the proposed method in both air and other media (e.g., water).

Seasonal variability in chromophoric dissolved organic matter in the Sakawa River and Sagami Bay, Japan

We investigated the chromophoric dissolved organic matter (CDOM) of river water in the Sakawa River and of surface water in the vicinity of the river’s mouth in Sagami Bay, Japan, during the period from July 2003 to July 2004. Absorption by CDOM was modeled as a logarithmic function. As a qualitative index of CDOM, the slope (S) of this function was estimated for a wavelength range from 280 to 500 nm. As a quantitative index of CDOM, the integration of absorption was determined between 280 and 500 nm (Σ280500aCDOM). High seasonal variability of S values was observed at the marine station. The S values at the upstream stations were related to chlorophyll a concentrations but not to bacterial abundance, whereas the integrated values at upstream stations were correlated with precipitation. Seasonal variability in the integrated values was low at the downstream stations, where the effect of effluent from nonpoint sources and sewage treatment plants was strong. Anthropogenic CDOM at the downstream stations appeared to be degraded by microbial utilization and photodegradation, whereas terrestrially derived CDOM at the upstream stations was less degraded. These qualitative differences in CDOM and the marked effect of dilution by seawater near the Sakawa River mouth suggest that the dynamics of CDOM in riverine and coastal environments should be studied with careful consideration of both spatial and temporal variations, particularly in small estuaries.

Absolute scale structure from motion using a refractive plate

Three-dimensional (3D) measurement methods are becoming more and more important to obtain information about the surrounding environment in many fields. Structure from Motion is one 3D measurement method using a single camera. This technique calculates the 3D reconstruction of objects from images captured by a single camera with motion. The camera motion can be estimated simultaneously as well as 3D information of objects. However, it is impossible to calculate the absolute scale of objects using Structure from Motion. Only the relative position can be obtained. In this paper, we propose a Structure from Motion method which can calculate the absolute scale of objects using refraction. Refraction occurs when light ray passes through different media. The absolute scale can be calculated using this change in light ray path. In order to generate the refraction, a refractive plate is placed in front of a camera. In a previous study we proposed a Structure from Motion method using refraction. However, the refractive plate was required to be placed perpendicular to the optical axis of the camera. In this new method, the refractive plate can be placed with any orientation in front of camera. In this aspect, the proposed method is more general than the previous one.