In forested headwater streams, various types of tree-derived materials such as leaf litter and woody debris are transported downstream through channel networks. Little is known about their characteristics and the mechanisms of their export, especially woody debris export. We review the roles of woody debris in streams from the aspects of geomorphology, ecology, erosion control engineering and water chemistry. We also demonstrate three processes, i.e., production, transport and retention, that affect woody debris export from forested catchments to provide needed information for water environment research.

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The total amount of phosphorus in a volcanic ash soil type adsorbent adsorbing phosphate from secondary effluent (used volcanic ash soil type phosphate adsorbent) is 13.8gP · kg^-1, mainly consisting of aluminum combination type phosphorus, and the amount of citrate-soluble phosphorus is 57%. A though this used volcanic ash soil type phosphate adsorbent is not suitable as a phosphate fertilizer according to the Fertilizer Regulation Law, it is found suitable as a soil amendment matter with a phosphate supply function because of its high amount of citrate-soluble phosphorus. The soil physics of the subsoil of andosol seldom changes with the application of the used volcanic ash soil type phosphate adsorbent. However, this absorbent has a large effect of promoting the growth of Brassica campestris cv. Komatsu, and is more effective than superphosphate. Moreover, its phosphorus adsorption rate low at only 0.8%, which proves that it is very promising for soil reduction and recycling.

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The perfluorinated surfactants, perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) have been reported to be present in the environment. Their behaviors in the environmental, however, are still unknown. In this study, we measured their concentrations in seawater and sediment from Tokyo Bay and in the waters of six major rivers that run into the bay. Then, their mass balances and behaviors in the bay were estimated. PFOS and PFOA existed mainly in the dissolved phase in water. The estimated annual input of PFOS from the rivers was 74 ∼ 346 kg · year^-1, which was similar to the total amount of PFOS outflow to the ocean (20 ∼ 350 kg · year^-1) and the amount of PFOS sedimentation to the bottom of the bay (1.3 kg · year^-1). On the other hand, the estimated annual input of PFOA from the rivers was 29 ∼ 148 kg · year^-1, which was much smaller than the total amount of PFOA outflow to the ocean (140 ∼ 1900 kg · year^-1). The amount of PFOA sedimentation was estimated to be negligible. These results suggest that the major source of PFOS in the bay is riverine transport. The results also indicate the existence of unknown PFOA sources around the coast of the bay and/or the possibility of a significant PFOA atmospheric deposition to the bay. The sediment was not a significant sink for the two compounds. Their environmental behaviors, therefore, are quite different from those of persistent organochlorine compounds.

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Trichloroethylene (TCE), a widespread and persistent environmental contaminant, is a regulated material in groundwater and soil. In this study, the electrochemical degradation of TCE was carried out using Pt/Ti-Ni as an anode-cathode material at a 0.1 A direct current. More than 99% TCE was degraded in a 69-hr reaction. The TCE degradation intermediates were identified as trichloroacetaldehyde, trichloroacetic acid, dichloroacetic acid, monochloroacetic acid, chloroform, and dichloromethane. From the chlorine balance during TCE electrochemical degradation, 98% TCE was converted to chlorine ions, chlorate ions, trichloroacetaldehyde, chloroform, and dichloroacetic acid. The degradation of the TCE intermediates was carried out to determine the electrochemical degradation pathways of TCE. The TCE degradation pathways are proposed to proceed as follows: as the main pathway, (i) TCE → trichloroacetaldehyde → trichloroacetic acid → dichloroacetic acid → monochloroacetic acid → low-molecular-weight materials; and as the subpathway, (ii) TCE → trichloroacetaldehyde → chloroform → dichloromethane → low-molecular-weight materials.

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