The isotopic signatures of nitrate in mountain streams indicate the dominant processes associated with nitrogen (N) export from a forested watershed. The nitrate concentrations sampled at 40 mountain streams around Mt. Tsukuba, and the oxygen (δ¹⁸O) and nitrogen isotope ratios (δ¹⁵N) of that nitrate, showed that the geophysical and geological characteristics of the basin significantly affected the N export processes in the forest watershed. From this study we discovered the following: 1) At seven sites, the isotopic signal (i. e., high δ¹⁸O) indicated that bulk precipitation was one of the primary nitrate sources in winter. Using two source mixing models, high δ¹⁸O levels in winter were only found in streams with low nitrate concentrations although precipitation substantially inflow. 2) Significant correlations were found between the geophysical/geological parameters of the basin and the nitrate concentration/isotope ratio parameters. These could mostly be explained by the increased nitrate production and consumption activity during the summer and the increase in the relative contribution of nitrate derived from bulk precipitation in winter.

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The willingness to pay (WTP) to engage in recreational fishing in a specific area of a mountain stream where a fishing-ban has been lifted and the factors affecting WTP were examined using an Internet-based contingent valuation method. The most popular information sources used to select a fishing site included “I have come here before” and “introduced by an acquaintance”, with selection rates of 70%. With regard to stream conditions in the selection process, “clear water” was the most popular at 73.3%. To increase fish numbers, a “method to improve the stream environment” was the preferred method at 68.5%. Recreational fishermen were willing to pay a premium of more than 20%, on average, once the ban was lifted. A higher degree of WTP was found for fishermen who valued factors such as “I have come here before”, as well as those who wanted to “catch large-sized fish” and “catch wild fish”. In addition, respondents who valued areas where there “are few anglers” and “the attitude of the anglers is good” when selecting a stream, and those who stated “create pools and rapids” as a preferred method to increase fish numbers, also had higher degrees of WTP. These respondents were generally characterized as living in households with higher annual incomes, and as having many years of experience in stream fishing.

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The monthly vertical profile of dissolved sulfide in the bottom sediments of the pen shell (Atrina pectinata) fishing ground at Arao, which is located offshore in northeastern Ariake Bay, was investigated from December 2007 to December 2008. The concentrations of dissolved sulfide in colder seasons were below 2 mgS L^-1, but increased to 9 mgS L^-1 as the sediment temperature increased. The monthly vertical profile of dissolved sulfide in the bottom sediments suggested that the death of Atrina pectinata was induced by an increase in hydrogen sulfide in the sediment.

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