A sound analyzer for measuring and analyzing the quality of singing sand was fabricated in order to clarify the deterioration factors of the sound-producing property of singing sand on the beach. The fundamental frequency measured by this instrument is used as an index. A technique that objectively evaluates the sound-producing property of singing sand was established. Using this technique, various environmental materials that affect the sound-producing property of singing sand were clarified. The environmental materials were sand moisture, precipitated salts from seawater, water-insoluble materials in fine powder state, and heavy oil and surfactant from environmental pollutants. Generally, the sound-producing property of singing sand deteriorates in the presence of these environmental materials. However, it was proven that the sound-producing property of singing sand is improved by the existence of moisture, heavy oil and surfactant at ultratrace levels. In addition, when physical forces, like vibration was applied to the sand particles, the sound-producing property of singing sand deteriorated, and actually disappeared. It was also proven that sand particle size has no effector the sound-producing property of singing sand.

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Alkylbenzyldimethylammonium chlorides (BACs) have been widely used as cationic surfactants with antiseptic properties, as disinfectants and in hair cosmetics. We developed a method for determining BACs in wastewater and sediment samples by liquid chromatography — mass spectrometry. C₁₂, C₁₄, and C₁₆ alkyl BACs are the major components in commercial products, and we therefore developed a determination method for these compounds. The detection limit for water samples was less than 0.01 μg · l^-1. Instrumental detection limits (IDLs), calculated from replicate analyses of standards, ranged from 0.00066 (C₁₄BAC) to 0.00284 (C₁₂BAC) μg · l^-1. Method detection limits (MDLs), calculated from replicate analyses of spiked purified water, were 0.00609 (C₁₂BAC) to 0.00803 (C₁₆BAC) μg · l^-1. Total method recoveries of purified water, ranged from 71.3% (C₁₆BAC) to 86.0% (C₁₂BAC) with relative standard deviations of 3.7% (C₁₂BAC) to 5.9% (C₁₆BAC). Recoveries of river water and sea water, ranged from 62.7% (C₁₆BAC) to 83.9% (C₁₂BAC). MDLs for sediments ranged from 0.821 (C₁₂BAC) to 0.963 (C₁₆BAC) μg · kg^-1 and recoveries of sediment, ranged from 63.9% (C₁₆BAC) to 87.6% (C₁₆BAC).

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The change in the sound-producing property of singing sand and its controlling factors were investigated at five investigation spots at Kotohikihama-beach over 6 years in order to clarify the factors in the deterioration of the sound-producing property of singing sand. As a result, it was proven that the sound-producing property deteriorated with the adherence of precipitated salts from seawater or silts and clays to the sand particle surface, which, except for moisture, markedly affects the sound-producing property. Such silts and clays had compositions the same as singing sand, and it was found that the feldspar component was more abundant than that in singing sand. Their particle size was about 10 μm or less caused by weathering or abrasion. Still, it is necessary to take removal countermeasure for these silts and clays, because the contamination of these materials in the sand layer seems to be mainly artificial. Surfactants and tobacco ashes that affect the sound-producing property were also investigated. However, these effects in the field could not be observed. The effect on singing sand by the NAKHODKA heavy oil spill incident, which occurred in 1997 during the investigation period, was also investigated. The pollution effect on singing sand by heavy oil was observed. However, it was found that the sound-producing property did not deteriorate ever in the presence of the oil.

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The objective of this study was to evaluate the restoration of eelgrass (Zostera marina L.) beds by filling up borrow pits along the coast of Iwakuni, in the Seto Inland Sea, Japan. We constructed an eelgrass habitat at the edge of previously constructed borrow pits in eelgrass beds by filling up the pits with natural sediment. We monitored sand movement, underwater irradiance and eelgrass shoot density in the constructed and natural habitats. Sand movement in the constructed habitat was from -8 cm to 9 cm, which is slightly different from that in the natural habitat. The averaged underwater irradiance in the constructed habitat was more than 3 mol photons · m^-2 · day^-1, which was the amount necessary for eelgrass. Eelgrass disappeared after typhoon occurrences in 2004-2006, whereas seedlings of eelgrass have continuously appeared in the constructed and natural habitats every winter. These results suggest that the restoration of eelgrass habitats by filling up borrow pits is a useful technique for eelgrass bed restoration.

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