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Matsumoto S.,The University of Shimane | Kasuga J.,The University of Shimane | Taiki N.,Nihon Mikuniya Corporation | Makino T.,Japan National Institute for Agro - Environmental Sciences | Arao T.,Japan National Institute for Agro - Environmental Sciences
Catena | Year: 2015

There are many rice paddy fields with relatively high arsenic (As) concentrations in areas that have not been subjected to countermeasures because the As level was below the criterion value established by the Agricultural Land Soil Contamination Prevention Law in Japan. To reduce the risk of excessive As in rice paddy fields using agronomic methods applicable to common farming practices, we examined the effect of the application of iron (Fe) and silicate materials on As uptake by rice plants in bottomless concrete frames filled with soil collected from an area surrounding a former As-polluted region. Following the application of calcium silicate slag at a rate of 0.5 kg m-2, no significant effect was observed on the As concentration in rice grain or straw, but the available silicate in the soil was increased. The application of Fe materials at a rate of 0.5 kg m-2 resulted in a significant reduction of the As concentration in grain and straw, as shown by an analysis of variance. The lowest concentrations of As in both grain and straw were obtained with the application of a metal Fe powder (EM), followed by that with an Fe oxide material (FB), a converter furnace slag (FM), and the control. The EM and FB applications both significantly reduced the 1M HCl-soluble As concentration in soil compared to the control. The levels of both acid ammonium oxalate extractable Fe (Fe-ox) and citrate-bicarbonate-dithionite extractable Fe (Fe-CDB) in the soil were significantly increased by the application of EM and that of FB compared to the FM and the control. A negative significant correlation was obtained between the amount of 1M HCl-soluble As and two types of free Fe oxide. These results suggest that the available As in soil was strongly fixed with the Fe oxides that were increased by the application of Fe materials, and that the decrease of available As in the soil induced a decrease in the As uptake by rice plants. The application of Fe materials will thus be effective to lower or prevent the risk of the rice cultivation in paddy fields with relatively high levels of As. © 2015 Elsevier B.V. Source


Matsumoto S.,The University of Shimane | Kasuga J.,The University of Shimane | Taiki N.,Nihon Mikuniya Corporation | Makino T.,Japan National Institute for Agro - Environmental Sciences | Arao T.,Japan National Institute for Agro - Environmental Sciences
Journal of Plant Interactions | Year: 2015

To reduce the risk of excessive arsenic (As) in rice by using agronomic methods applicable to common farming in uncontaminated soil with As, we examined the effect of different start periods of drainage after heading and the application of iron (Fe) or silicate (Si) materials in concrete frames filled with soil collected from an area surrounding a former As-polluted region. The concentration of As in the grain decreased with the early start of drainage, whereas the cadmium (Cd) concentration increased. Thus, maintaining the oxidative condition after heading significantly decreases the concentration of As in the grain. Fe material application significantly decreased the concentration of As in the grain compared to the control. The phosphorus (P) concentration ratio of grain to straw (which we regarded as the P distribution rate of grain and straw) was significantly lower with the delay of the start of drainage. Similar results were obtained in the solution culture experiment in which the P level was decreased by half in the culture solution. A negative correlation between the P concentration ratio of grain to straw and the concentration of As in the grain was observed, indicating that an increase in the P translocation rate from straw to grain would inhibit the accumulation of As in the grain due to the competition of P and As. Further evaluations of the effects of Fe, Si, and P on water management and fertilization are needed to reduce the risk of As accumulation in rice grain. © 2015 The Author(s). Published by Taylor & Francis. Source


Kanaya G.,Japan National Institute of Environmental Studies | Nakamura Y.,Japan National Institute of Environmental Studies | Koizumi T.,Nihon Mikuniya Corporation | Yamada K.,Japan National Institute of Environmental Studies | Yamada K.,Seikai National Fisheries Research Institute
Marine Environmental Research | Year: 2015

We conducted a one-year survey of macrozoobenthic community structure at 5 stations in a eutrophic canal in inner Tokyo Bay, focusing on the impacts of hypoxia, sediment H2S, and species interaction in the littoral soft-bottom habitats. Complete defaunation or decreasing density of less-tolerant taxa occurred under hypoxia during warmer months, especially at subtidal or sulfidic stations; this was followed by rapid recolonization by opportunistic polychaetes in fall-winter. Sedimentary H2S increased the mortality of macroinvertebrates under hypoxia or delayed population recovery during recolonization. The density of several polychaetes (e.g., Pseudopolydora reticulata) declined in winter, coincident with immigration of the predator Armandia lanceolata. This suggests that absence of A.lanceolata under moderate hypoxia enabled the proliferation of prey taxa. We conclude that oxygen concentration, sediment H2S, and hypoxia-induced changes in species interactions are potential drivers for spatiotemporal changes in macrozoobenthic assemblage structure in hypoxia-prone soft-bottom communities. © 2015 Elsevier Ltd. Source


Nakamura Y.,Japan National Institute of Environmental Studies | Nakano T.,Nagasaki University | Yurimoto T.,Seikai National Fisheries Research Institute | Maeno Y.,Seikai National Fisheries Research Institute | And 2 more authors.
Fisheries Science | Year: 2010

We assessed the reproductive cycle of the venerid clam Meretrix lusoria by histological analysis of the gonads. Individuals for study were collected from natural populations on the Shirakawa tidal flat, Ariake Sound, and from populations that had been transplanted from the Shirakawa flat to the Oi flat in Tokyo Bay. In both study areas, the reproductive cycle was synchronized between sexes. Gonads of the clam started to develop in early spring and matured during the summer. Mass spawning occurred in the late summer/early fall. The clam matured at a shell length of 17-20 mm, which is much smaller than previously considered. While trophic conditions and salinity differed considerably in the two study areas, water temperatures showed similar seasonal changes (12°C during the winter and around 30°C during the summer). Thus, temperature probably controlled gonadal development. The coincidence of the period of spawning with the period of frequent intrusion of hypoxic waters into the tidal flats in Tokyo Bay suggests that such hypoxic events interfere with clam recruitment and are at least partly responsible for the disappearance of the natural population at this location. © 2010 The Japanese Society of Fisheries Science. Source

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