Showing papers in "Geographical reports of Tokyo Metropolitan University in 2014"

Chemical characterization of volcanic glass shards by energy dispersive X-ray spectrometry with EDAX Genesis APEX2 and JEOL JSM-6390

Abstract: A chemical characterization of individual volcanic glass shard by electron-beam (E-beam) methods including SEM-EDS is effective for tephra fingerprinting. We installed a new SEM-EDS system composed of EDAX Genesis APEX2 and JEOL JSM-6390. This paper discusses reproducibility, accuracy, and precision of this system based on the analytical data sets of three representative Japanese widespread tephras and four provided samples by INTAV intercomparison. 710 analyses on homogeneous natural glass shards extracted from a representative Japanese widespread tephra (Aira-Tn: AT) under the same analytical conditions demonstrate reproducibility of measurements and absence of machine drift. For testing inter-laboratory reproducibility, three representative Japanese widespread tephras (AT, K-Ah, and Toya) and four natural glasses (rhyolitic Lipari obsidian, phonolitic Sheep Track tephra, basaltic Laki 1783 A.D. tephra, rhyolitic Old Crow tephra) were selected. Results of comparison prove that the new system mostly enabled us to determine the major oxide concentrations comparable with other laboratories. However, in case of lower oxide concentrations less than ca. 0.3 wt% such as TiO 2 , MnO, and MgO, similarity and difference in concentrations are not significant because these values are less than the detection limit of SEM-EDS analysis. Also, results of comparison suggest that attention should be paid in determination of glass chemistry with higher content of CaO and Na 2 O concentrations for basaltic and phonolitic tephras such as Laki 1783 A.D. and Sheep Track tephras.

Niche differentiation of fungivorous Acari and Collembola in Japanese beech forest soils

Abstract: Acari and Collembola are the two most abundant microarthropods in the soil and are found in a wide range of soil habitats. Both animals relatively share the same trophic level as fungivorous microarthropods which directly influence the soil fertility by stimulating the microbial activity, play important roles in fungal dispersions and its relations to plant nutrient uptake. With their high abundance in the soil, the niche differentiation between both animals towards fungal communities in soil remains uncertain. Many studies have been conducted to understand the niche differentiation of fungivorous Acari and Collembola sharing the soil fungal communities as resources, such as through gut content analyses and fungal food preference experiments. Nevertheless these methods may not reflect feeding processes in the field. The community profiling method, Terminal Restriction Fragment Length Polymorphism (T-RFLP) analysis was offered as a molecular technique performed to describe the fungal community structure associated with both animals to understand the niche differentiation in the field. Four Japanese Beech forest soils in Northeast (Akita, Choukai, and Iwaki) and Central (Nagano) Japan were chosen as study sites. Results suggested that even though Acari and Collembola showed associations with relatively different fungal communities, overlapping niches were also identified. Among the studied area, the southernmost area (Nagano) had the highest animal abundance in the soil and the least niche overlap between Acari and Collembola.

Overview of lightning observation network with ELF-VLF electromagnetic measurements over Tokyo Metropolitan Area

Abstract: An Extremely Low Frequency−Very Low Frequency (ELF−VLF) radio wave observation network system in the Tokyo metropolitan area has been newly established to detect lightning activity and investigate the characteristics of heavy rainfall induced by thunderstorms. The VLF electromagnetic waveforms induced by lightning (commonly known as “sferics”) were observed at three sites (Hachioji, Yokosuka, and Koto) from the Baiu season until mid-summer 2013. The observed VLF sferics were used to detect lightning frequency and estimating the geo-locate the lightning source according to the time of arrival (TOA) method. The preliminary results suggest that this system could detect the lightning signals from convective cloud systems, despites differences in detection sensitivity and diurnal cycles between sites. Further studies are required to optimize the observation network system and refine the VLF sferics analysis method to enable the collection of high-accuracy lightning data.