A dispersion equation and dispersion coefficient for material transport in Inland Seas

To analyse material transport in inland seas, a horizontal two-dimensional dispersion equation is derived, and the dispersion coefficient due to the combined effect of vertical turbulent mixing and vertical shear of both a steady current and a tidal current is studied. In the present study, the assumption that velocity is uniform in horizontal planes is not necessary, and velocity has a free vertical profile; thus the dispersion coefficient formulated is general, and is represented by a tensor of the second order. The properties of the dispersion coefficient in the horizontal two-dimensional dispersion model are also investigated, and it is shown that the time-averaged dispersion coefficient due to the tidal current over a tidal period is approximately half that due to the steady current, if the velocity amplitude and the vertical profile of the tidal current are the same as those of the steady current (a similar result was presented byBowden (1965) for horizontal one-dimensional models). Finally, the dispersion coefficient in Hiuchi-Nada (Hiuchi Sound) in the central part of the Seto Inland Sea is evaluated by using the model. The values of the dispersion coefficient in that region range from 10³ cm² s^–1 to 10⁵ cm² s^–1 when vertical turbulent diffusivity is taken to be 50 cm² s^–1.     

Three-dimensional mapping of red stingray (Dasyatis akajei) movement with reference to bottom topography

Most demersal fishes maintain strong relations with bottom substrates and bottom depths and/or topography during their lives. It is important to know these relations to for understand their lives. In Tokyo Bay, red stingray, Dasyatis akajei, classified as near-threatened species by IUCN, has increased since the 1980s. It is a top predator and engages in ecosystem engineer by mixing the sand bed surface through burring behavior, and greatly influences a coastal ecosystem. It is reported that this species invades in plage and tidal flats and has sometimes injured beachgoers and people gathering clams in Tokyo bay. Thus, it is necessary to know its behavior and habitat use to avoid accidents and to better conserve the biodiversity of ecosystems. However, previous studies have not examined its relationship with the bottom environment. This study aims to describe its behavior in relation to the bottom environment. We sounded three dimensional bottom topography of their habitat off Kaneda Cove in Tokyo Bay with interferometric sidescan sonar system and traced the movement of red stingrays by attaching a data logger system to survey their migration. The results revealed that red stingray repeated vertical movement between the surface and bottom, and used not only sand beds but also rocky beds.

     

Relationship between groundwater flow estimated by soil temperature and slope failures caused by heavy rainfall, Shikoku Island, southwestern Japan

Most of the slope failure disasters in a humid area such as that of Japan are caused by heavy rain. However, even for the case of heavy rainfall that occurs once in every 10 years, total area of slope failures seldom exceeds 10% of a watershed. From this background, we focused on the vein-like groundwater flows that increase pore-water pressure, and clarified the relationship between distributions of slope failures and groundwater veins. In this study, a 1-m-depth ground temperature survey and water-chemistry analyses at springs and boreholes were conducted in Zentoku area of Shikoku Island, southwestern Japan, to grasp the distribution of groundwater veins and their sources. Subsequently, slope-stability was analyzed to investigate the relationship between groundwater veins and slope failures at study sites. These results lead to the following conclusions: The slope failures appear to concentrate around shallow groundwater veins and groundwater veins rising from deep layers. This means that slope failures caused by these groundwater veins in addition to rainfall. Two types of groundwater originate in the deep layers: one has short storage time as indicated by the fact that dissolved substances are low; the other is stored for a lengthy period as noted by a high concentration of dissolved substances. By combining the results of stability analyses and distribution of groundwater veins, it is suggested that prediction of zones with high potential for slope failure can be more accurate.     

Short-Timescale Chemo-Mechanical Effects and their Influence on the Transport Properties of Fractured Rock

Anomalous changes in permeability are reported in fractures circulated by fluids undersaturated with respect to the mineral host. Under net dissolution and net removal of mineral mass, fractures may alternately gape or seal, depending on the prevailing mechanical and chemical conditions. The influence on transport properties is observed to be large, rapid, and irreversible: Permeabilities may change by two orders of magnitude in a month, and the direction of permeability change may switch spontaneously, for no apparent change in environmental forcing. These behaviors are apparent in continuous circulation experiments conducted on fractures in novaculite and limestone, intermittently imaged by X-ray CT. In novaculite, permeability reduces by two orders of magnitude as silica is net removed from the sample. Surprisingly, these changes can occur at modest temperatures (~80°C) and stresses (~3.5 MPa), where compaction progresses as temperatures are incremented. Isothermal (~20°C) circulation tests in limestone show similar compaction driven by pressure solution. Where circulation remains undersaturated in Ca, the change in permeability spontaneously switches from net reduction to net increase as a wormhole forms. The surprising magnitude and rapidity of these changes are investigated in the context of the competition between stress- and chemistry-mediated effects.     

Optimization of causative factors using logistic regression and artificial neural network models for landslide susceptibility assessment in Ujung Loe Watershed,South Sulawesi Indonesia

Landslide susceptibility maps(LSMs) play a vital role in assisting land use planning and risk mitigation. This study aims to optimize causative factors using logistic regression(LR) and an artificial neural network(ANN) to produce a LSM. The LSM is produced with 11 causative factors and then optimized using forward-stepwise LR(FSLR), ANN, and their combination(FSLR-ANN) until eight causative factors were found for each method. The ANN method produced superior validation results compared with LR. The ROC values for the training data set ranges between 0.8 and 0.9. On the other hand, validation with the percentage of landslide fall into LSM class high and very high, ANN method was higher(92.59%) than LR(82.12%). FSLR-ANN with nine causative factors gave the best validation results with respect to area under curve(AUC) values, and validation with the percentage of landslide fall into LSM class high and very high. In conclusion, ANN was found to be better than LR when producing LSMs. The best Optimization was combination of FSLR-ANN with nine causative factors and AUC success rate 0.847, predictive rate 0.844 and validation with landslide fall into high and very high class with 91.30%. It is an encouraging preliminary model towards a systematic introduction of FSLR-ANN model for optimization causative factors in landslide susceptibility assessment in the mountainous area of Ujung Loe Watershed.     

Thermal Image Velocimetry

A method for measuring the two-dimensional distribution of wind velocity vectors near a surface exposed to solar radiation, by tracking brightness temperature images instead of particle images, is proposed. It is based on time-sequential thermography with the algorithm used for particle image velocimetry. This thermal image velocimetry (TIV) was tested on a full-scale building wall covered by polystyrene boards attached side-by-side over a vertically elongated area measuring 22.2 m by 2.73 m. A thermal infrared camera was installed 8 m from the test wall to capture the wall-surface temperature at 30 Hz frequency. A sonic anemometer was also installed 35 mm from the surface used for validation of the TIV. The advection velocity estimated from thermal infrared imagery had a linear relationship with the wind velocity measured by the sonic anemometer, irrespective of the wind speed and direction. This linear slope was multiplied by the advection velocity of the thermal infrared image to rescale it to the wind velocity, and the term ‘TIV velocity’ was then used. A histogram and power spectra of the TIV velocity showed quantitatively good agreement with the velocity measured by the sonic anemometer, except for the high-frequency region of the spectra, where the TIV velocity was overestimated compared with that of the sonic anemometer. The method was also tested on ground covered by artificial turf to demonstrate its application to a horizontal plane with a wider area, extending for more than 80 m by 60 m.     

Feeding Strategy of Japanese Sand Lance Larvae in Relation to Ciliated Protozoa in the Vicinity of a Thermohaline Front

Larval feeding and survival strategies are described on a Japanese sand lance, Ammodytes personatus Girard, collected in the vicinity of a thermohaline front in the Ise Bay, in comparison with those of other predominant larvae, Hexagrammos spp. and Sebastiscus marmoratus (Cuvier). First-feeding A. personatus larvae (3.1–3.9 mm NL) fed primarily on tintinnid ciliates, subsequently switching to copepod nauplii (4.0–7.9 mm NL larvae) and post-naupliar copepods (8.0–11.3 mm NL larvae). First-feeding Hexagrammos spp. larvae (6.5–6.9 mm NL) fed primarily on post-naupliar copepods, and first-feeding S. marmoratus larvae (<4.0 mm NL), mostly on copepod nauplii. The different food preferences of these species at first-feeding were related to their different mouth widths (0.15–0.19, 0.52–0.56 and 0.32–0.40 mm, respectively) and/or body size (3.1–3.9, 6.5–6.9 and 3.2–3.9 mm NL, respectively). Ciliate-feeding by first-feeding A. personatus larvae was strongly related to the convergence of the larvae and their prey near the thermohaline front, densities of both being greater on the inshore side of the frontal zone. In conclusion, the aggregation of ciliates near the thermohaline front may have improved feeding conditions and survival of first-feeding A. personatus larvae.     

Crude oil bioremediation field experiment in the Sea of Japan

Experimental bioremediation of crude oil was conducted for approximately 3 months in the intertidal zone of the Sea of Japan, Hyogo Prefecture. Artificial mixtures of weathered Arabian light crude oil and sand taken from the experimental site were wrapped in polyester net envelopes. The envelopes were placed in drum-shaped acrylic vessels with perforated sides to facilitate seawater exchange. The vessels were laid in the intertidal area. Slow release nitrogen and phosphorus synthetic fertilizer granules were added to the oil-sand mixtures in three different amounts. Some oil-sand mixtures were unfertilized controls. The oil-sand mixtures were periodically sampled and changes in the composition of the residual oils were monitored. Oil samples were subjected to gas chromatography coupled with mass spectrometry for analysis of some representative semi-volatile aliphatic and aromatic compounds. All values for each analyte were normalized against that of hopane to evaluate the extent of oil biodegradation. Significant increases in the concentrations of both nitrogen and phosphorus were found in the fertilized sections in accordance with the amounts of added fertilizers. Although significant natural attenuation of oil was observed in the unfertilized sections, fertilization stimulated the degradation rate of the oil in the early stage of the experimental term. The extent of the oil biodegradation increased as the amount of added fertilizer increased. However, the final degradation efficiencies for each oil component in the fertilized sections were not significantly different from those in the unfertilized sections, and the degradation of each oil component had almost ceased after 6 weeks. We conclude that excessive amounts of macronutrients are required to accelerate oil biodegradation and that fertilization is only effective in the early stages.     

A compound-specific n-alkane δC and δD approach for assessing source and delivery processes of terrestrial organic matter within a forested watershed in northern Japan

We measured molecular distributions and compound-specific hydrogen (δD) and stable carbon isotopic ratios (δ¹³C) of mid- and long-chain n-alkanes in forest soils, wetland peats and lake sediments within the Dorokawa watershed, Hokkaido, Japan, to better understand sources and processes associate with delivery of terrestrial organic matter into the lake sediments. δ¹³C values of odd carbon numbered C₂₃-C₃₃n-alkanes ranged from −37.2‰ to −31.5‰, while δD values of these alkanes showed a large degree of variability that ranged from −244‰ to −180‰. Molecular distributions in combination with stable carbon isotopic compositions indicate a large contribution of C3 trees as the main source of n-alkanes in forested soils whereas n-alkanes in wetland soil are exclusively derived from marsh grass and/or moss. We found that the n-alkane δD values are much higher in forest soils than wetland peat. The higher δD values in forest samples could be explained by the enrichment of deuterium in leaf and soil waters due to increased evapotranspiration in the forest or differences in physiology of source plants between wetland and forest. A δ¹³C vs. δD diagram of n-alkanes among forest, wetland and lake samples showed that C₂₅-C₃₁n-alkanes deposited in lake sediments are mainly derived from tree leaves due to the preferential transport of the forest soil organic matter over the wetland or an increased contribution of atmospheric input of tree leaf wax in the offshore sites. This study demonstrates that compound-specific δD analysis provides a useful approach for better understanding source and transport of terrestrial biomarkers in a C3 plant-dominated catchment.     

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.