Browsing by Author "Fujimura, Hiroyuki"

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    Continuous-flow complete-mixing system for assessing the effects of environmental factors on colony-level coral metabolism
    (2008-04) Fujimura, Hiroyuki; Higuchi, Tomihiko; Shiroma, Kazuyo; Arakaki, T.; Hamdun, Asha; Nakano, Yoshikatsu; Oomori, Tamotsu
    A small-scale chamber experimental system was designed to study the effects of temperature on colony-level coral metabolism. The system continuously supplies fresh seawater to the chamber, where it is mixed immediately and completely with the seawater already present. This continuous-flow complete-mixing system (CFCM system), in conjunction with theoretical equations, allows quantitative determination of chemical uptake and release rates by coral under controlled environmental conditions. We used the massive hermatypic coral Goniastrea aspera to examine variations in pH, total alkalinity, and total inorganic carbon for 16 days at 27 degrees C under controlled light intensities (300 and 0 micromol m(-2) s(-1)). We confirmed the stability of the CFCM system with respect to coral photosynthetic and calcification fluxes. In addition, we obtained daily photosynthetic and calcification rates at different temperatures (27 degrees C, 29 degrees C, 31 degrees C, and 33 degrees C). When seawater temperature was raised from 31 degrees C to 33 degrees C, the gross primary production rate (Pgross) decreased 29.5%, and the calcification rate (G) decreased 85.7% within 2 days. The CFCM system allows quantitative evaluation of coral colony chemical release and uptake rates, and metabolism.
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    Photochemical activity of seawater contaminated with red soil in the northern part of Okinawa
    (2003-08) Hamdun, Asha; Okada, Kazunori; Fujimura, Hiroyuki; Arakaki, T.; Taira, Hatsuo
    Hydroxyl radical (. OH) as a most reactive oxidant, posses an oxidizing power to control the lifetime of many synthetic and natural organic compounds in natural waters. Northern part of Okinawa Main Island is experiencing high soil erosion rate, particularly by acidic reddish soil that contains about 3.3- 5.3% of Fe. Past work has shown that low pH and high iron concentration favour OH fo
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    Photochemical Formation of Hydroxyl Radical in Red-Soil-Polluted Seawater in Okinawa, Japan Potential Impacts on Marine Organisms
    (2004-11) Arakaki, T.; Hamdun, Asha; Okada, Kazunori; Kuroki, Y.; Ikota, Hirotsugu; Fujimura, Hiroyuki; Oomori, Tamotsu
    Development of pineapple farmlands and construction of recreational facilities caused runoff of red soil into coastal ocean (locally termed as red-soil-pollution) in the north of Okinawa Island, Japan. In an attempt to understand the impacts of red soil on oxidizing power of the seawater, we studied formation of hydroxyl radical (OH radical), the most potent oxidant in the environment, in red-soil-polluted seawaters, using 313 nm monochromatic light. Photo-formation rates of OH radical showed a good correlation with dissolved iron concentrations (R = 0.98). The major source of OH radical was found to be the Fenton reaction (a reaction between Fe(II) and HOOH). The un-filtered red-soil-polluted seawater samples exhibited faster OH radical formation rates than the filtered samples, suggesting that iron-bearing red soil particles enhanced formation of OH radical.
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    Simultaneous Measurement of Hydrogen Peroxide and Fe Species (Fe(II) and Fe(tot)) in Okinawa Island Seawater: Impacts of Red Soil Pollution
    (2005-05) Arakaki, T.; Fujimura, Hiroyuki; Hamdun, Asha; Okada, Kouichirou; Kondo, Hiroaki; Oomori, Tamotsu; Tanahara, Akira; Taira, Hatsuo
    The northern part of Okinawa Island suffers from red soil pollution—runoff of red soil into coastal seawater—which damages coastal ecosystems and scenery. To elucidate the impacts of red soil pollution on the oxidizing power of seawater, hydrogen peroxide (HOOH) and iron species including Fe(II) and total iron (Fe(tot), defined as the sum of Fe(II) and Fe(III)) were measured simultaneously in seawater from Taira Bay (red-soil-polluted sea) and Sesoko Island (unpolluted sea), off the northern part of Okinawa Island, Japan. We performed simultaneous measurements of HOOH and Fe(II) because the reaction between HOOH and Fe(II) forms hydroxyl radical (•OH), the most potent environmental oxidant. Gas-phase HOOH concentrations were also measured to better understand the sources of HOOH in seawater. Both HOOH and Fe(II) in seawater showed a clear diurnal variation, i.e. higher in the daytime and lower at night, while Fe(tot) concentrations were relatively constant throughout the sampling period. Fe(II) and Fe(tot) concentrations were approximately 58% and 19% higher in red-soil-polluted seawater than in unpolluted seawater. Gas-phase HOOH and seawater HOOH concentrations were comparable at both sampling sites, ranging from 1.4 to 5.4 ppbv in air and 30 to 160 nM in seawater. Since Fe(II) concentrations were higher in red-soil-polluted seawater while concentrations of HOOH were similar, •OH would form faster in red-soil-polluted seawater than in unpolluted seawater. Since the major scavenger of •OH, Br−, is expected to have similar concentrations at both sites, red-soil-polluted seawater is expected to have higher steady-state •OH concentrations.