In order to elucidate the behavior and the seasonal variation of eutrophication substances in the Yodo River system, the dissolved inorganic nitrogen compounds, dissolved inorganic phosphate, total dissolved nitrogen (TDN), total dissolved phosphate (TDP) and dissolved organic carbon (DOC) were periodically observed during March 2001 to February 2002. Concentrations of TDN and TDP were near doubled downstream from the confluence of tributaries, the Katsura and Kizu Rivers. However, that of DOC did not increase significantly in the same interval. These results suggested that the nitrogen and phosphorus compounds from the tributaries had much influence on the water pollution of the Yodo River system compared to those of the main stream. The loads per year of TDN, TDP and DOC from the Yodo River to Osaka Bay were calculated to be 8,370, 444 and 11,700 ton/yr, respectively.

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To investigate soil-air surface exchange of mercury, we observed mercury emission fluxes from soil surfaces at two open-field sites and a forest site using a flux chamber method. In addition, we carried out laboratory experiments in which factors affecting mercury fluxes were controlled. The field observations showed that the mercury fluxes increased with increasing soil surface temperatures and solar radiation. From the laboratory experiments, it was clear that soil moisture content affects the variations in mercury fluxes, which are dependent on soil types. Also, it was inferred that organic carbon content of soil affects the mercury fluxes from soils. Based on the field and laboratory experiments, we found the mercury fluxes at the forest site can be estimated approximately from the single parameter of soil surface temperature. The estimated annual mercury emission flux (40 μg m^-2) at the study forest site has been comparable to the current mercury deposition fluxes (10-26 μg m^-2) in Japan. This suggests that soil-air surface exchange of mercury is an important process governing the dynamics of atmospheric mercury in Japan.

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The biogeochemical interactions and feedbacks between the ocean and the atmosphere affect and are affected by climate and environmental changes. I have been studying the variability of chemical composition and behavior of marine atmospheric aerosols from the biogeochemical point of view since the early 1980's. My contributions to our understanding of atmospheric aerosol processes are reviewed here: Anthropogenic and mineral dust aerosols from the Asian continent are found to be transported over the large area of the North Pacific Ocean and to affect the global radiation budget and climate. Atmospheric transport of the aerosols, their chemical and physical interactions and scavenging processes within the marine boundary layer are explained in detail. The impact of atmospheric deposition flux over the sea surface is also found to strongly influence chemical and biological processes in water column and affect rates of marine biological activities. Marine aerosol properties are suggested to be altered by feedbacks from marine biological processes. To achieve the quantitative understanding of the linkages among the ocean, the atmosphere and climate, it is necessary to collaborate with groups of marine biology, physical oceanography, meteorology and modeling. Finally, I am indeed honored to have been selected to receive the 2004 Geochemical Society of Japan Award.

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[in Japanese]

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