Published Papers - Yasumoto Jun

Coral Decline Linked to Exchangeable Phosphate in Seawater from Coastal Calcareous Sediments, as Evidenced in Sekisei Lagoon, Japan

Jun Yasumoto, Mariko Iijima, Akira Iguchi, Takashi Nakamura, Ryogo Takada, Mina Yasumoto-Hirose, Yuichi Iwasaki, Tetsuo Yasutaka, Kanami Mori-Yasumoto, Ryuichi Shinjo, Ryota Ide, Alice Yamazaki, Nanami Mizusawa, Yoshikazu Ohno, Atsushi Suzuki, Shugo Watabe, Ko Yasumoto

Marine Biotechnology ( Springer Nature )    2025.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

Adverse effects of total phosphate load from the environment on the skeletal formation of coral juveniles

Mariko Iijima, Ko Yasumoto, Jun Yasumoto, Akira Iguchi, Mina Yasumoto-Hirose, Kanami Mori-Yasumoto, Nanami Mizusawa, Mitsuru Jimbo, Kazuhiko Sakai, Atsushi Suzuki, Shugo Watabe

Marine Pollution Bulletin ( Elsevier )    2025.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Effect of Groundwater Flow on Microbial Activity in a Porous Limestone Groundwater

Nakaya, S; Deno, T; Yasumoto, J; Takada, R

ECOHYDROLOGY   18 ( 1 )   2025.01 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The Role of Polyamines in pH Regulation in the Extracellular Calcifying Medium of Scleractinian Coral Spats

Azusa Kubota, Yoshikazu Ohno, Jun Yasumoto, Mariko Iijima, Michio Suzuki, Akira Iguchi, Kanami Mori-Yasumoto, Mina Yasumoto-Hirose, Tsuyoshi Sakata, Takaaki Suehiro, Kaho Nakamae, Nanami Mizusawa, Mitsuru Jimbo, Shugo Watabe, Ko Yasumoto

Environmental Science & Technology ( American Chemical Society )    2024.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Polyamine impact on physiology of early stages of reef-building corals–Insights from rearing experiments and RNA-Seq analysis

Kodai Gibu*, Nanami Mizusawa, Mariko Iijima, Yoshikazu Ohno, Jun Yasumoto, Ko Yasumoto, Akira Iguchi

Scientific Reports ( Springer Nature )    2024.10 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Reply to discussion of "An assessment of small Island hydrological research activity conducted in the Oceania Region"<SUP>1</SUP>

Leong, C; Solomone, M; Shinjo, R; Tomojiri, D; Uchiyama, C; Yasumoto, J; Razafindrabe, B

HYDROLOGICAL SCIENCES JOURNAL ( Hydrological Sciences Journal )  69 ( 11 ) 1557 - 1559   2024.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Live imaging of center of calcification formation during septum development in primary polyps of Acropora digitifera

Yoshikazu Ohno, Anan Takahashi, Motosuke Tsutsumi, Azusa Kubota, Akira Iguchi, Mariko Iijima, Nanami Mizusawa, Takashi Nakamura, Atsushi Suzuki, Michio Suzuki, Jun Yasumoto, Shugo Watabe, Kazuhiko Sakai, Tomomi Nemoto, Ko Yasumoto

Frontiers in Marine Science   11   1406446   2024.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Recent studies have revealed that stony corals create their extracellular skeletons via biologically controlled calcification, in which amorphous calcium carbonate (ACC), regarded as precursors of aragonite crystals, have been observed at nanoscale using electron microscopy. However, the exact mechanism by which ACC is generated, and how it contributes to skeletal growth in coral calcifying tissue, remains enigmatic. The septal skeleton of an individual polyp is composed of radially aligned plates extending upward from the aboral calcifying tissue. This structure includes microstructure known as the centers of calcification (CoC). However, despite its importance, direct in vivo observation of septal growth has not been reported. Observations under transmitted illumination using polarized light microscopy on calcifying tissue of young Acropora digitifera revealed small crystals, a few micrometers in size, that accompany subtle movements and that emerge exclusively on the inner wall of the pocket in extracellular calcifying fluid (ECF). Crystal growth initiated from small, scattered crystals on a glass plate resembles this phenomenon observed in coral skeletons. Time-lapse photographs of 12 individuals in early primary polyp settlement revealed this process in three individuals, documenting 13 of these crystal events. This phenomenon occurred solely at the bases of subsequently formed septa. These crystals differ notably from fusiform crystals and from dumbbell-like or rod-like crystals growing individually. Upright two-photon microscopy captured movement of sub-micron-sized fluorescent calcein-accumulating particles, emphasizing their presence on the surface of the growing fronts of septa. Methodological advances that facilitate comprehensive in vivo observation of sub-micron-sized structures, calcein-accumulating particles to the skeleton, are needed to develop a more detailed understanding of coral skeletal growth.

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Metagenomic analysis of the microbial communities and associated network of nitrogen metabolism genes in the Ryukyu limestone aquifer

Maruyama, R; Yasumoto, K; Mizusawa, N; Iijima, M; Yasumoto-Hirose, M; Iguchi, A; Hermawan, OR; Hosono, T; Takada, R; Song, KH; Shinjo, R; Watabe, S; Yasumoto, J

SCIENTIFIC REPORTS ( Scientific Reports )  14 ( 1 ) 4356 - 14   2024.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Abstract While microbial biogeochemical activities such as those involving denitrification and sulfate reduction have been considered to play important roles in material cycling in various aquatic ecosystems, our current understanding of the microbial community in groundwater ecosystems is remarkably insufficient. To assess the groundwater in the Ryukyu limestone aquifer of Okinawa Island, which is located in the southernmost region of Japan, we performed metagenomic analysis on the microbial communities at the three sites and screened for functional genes associated with nitrogen metabolism. 16S rRNA amplicon analysis showed that bacteria accounted for 94–98% of the microbial communities, which included archaea at all three sites. The bacterial communities associated with nitrogen metabolism shifted by month at each site, indicating that this metabolism was accomplished by the bacterial community as a whole. Interestingly, site 3 contained much higher levels of the denitrification genes such as narG and napA than the other two sites. This site was thought to have undergone denitrification that was driven by high quantities of dissolved organic carbon (DOC). In contrast, site 2 was characterized by a high nitrate-nitrogen (NO₃-N) content and a low amount of DOC, and this site yielded a moderate amount of denitrification genes. Site 1 showed markedly low amounts of all nitrogen metabolism genes. Overall, nitrogen metabolism in the Ryukyu limestone aquifer was found to change based on environmental factors.

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Mechanism of denitrification in subsurface-dammed Ryukyu limestone aquifer, southern Okinawa Island, Japan

Oktanius Richard Hermawan, Takahiro Hosono, Jun Yasumoto, Ko Yasumoto, Ke-Han Song, Rio Maruyama, Mariko Iijima, Mina Yasumoto-Hirose, Ryogo Takada, Kento Hijikawa, Ryuichi Shinjo

Science of The Total Environment ( Elsevier BV )  912   169457 - 169457   2023.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Denitrification crucially regulates the attenuation of groundwater nitrate and is unlikely to occur in a fast-flowing aquifer such as the Ryukyu limestone aquifer in southern Okinawa Island, Japan. However, evidences of denitrification have been observed in several wells within this region. This study analyzed environmental isotopes (δ15NNO3 and ẟ18ONO3) to derive the rationale for denitrification at this site. Additionally, the presence of two subsurface dams in the study area may influence the processes involved in nitrate attenuation. Herein, we analyzed 150 groundwater samples collected spatially and seasonally to characterize the variations in the groundwater chemistry and stable isotopes during denitrification. The values of δ15NNO3 and δ18ONO3 displayed a progressive trend up to +59.7 ‰ and + 21 ‰, respectively, whereas the concentrations of NO3−–N decreased to 0.1 mg L−1. In several wells, the enrichment factors of δ15NNO3 ranged from −6.6 to −2.1, indicating rapid denitrification, and the δ15NNO3 to δ18ONO3 ratios varied from 1.3:1 to 2:1, confirming the occurrence of denitrification. Denitrification intensively proceeds under conditions of depleted dissolved oxygen concentrations (<2 mg L−1), sluggish groundwater flow with longer residence times, high concentrations of dissolved organic carbon (>1.2 mg L−1), and low groundwater levels during the dry season with precipitation rates of <100 mm per month (Jun–Sep). SF6 analysis indicated the exclusive occurrence of denitrification in specific wells with groundwater residence times exceeding 30 years. These wells are located in close proximity to the major NE–SW fault system in the Komesu area, where the hydraulic gradient was below 0.005. Detailed geological and lithological investigations based on borehole data revealed that subsurface dams did not cause denitrification while the major NE–SW fault system uplifted the impermeable basement rock of the Shimajiri Group, creating a lithological gap at an equivalent depth that ultimately formed a sluggish groundwater area, promoting denitrification.

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An assessment of small Island hydrological research activity conducted in the Oceania Region

Chris Leong, Maletina Solomone, Ryuichi Shinjo, Daiki Tomojiri, Christmas Uchiyama, Jun Yasumoto &Bam Razafindrabe

Hydrological Sciences Journal ( Taylor & Francis )    2023.09 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Effective use of farmland soil samples for N and O isotopic source fingerprinting of groundwater nitrate contamination in the subsurface dammed limestone aquifer, Southern Okinawa Island, Japan

28. Oktanius Richard Hermawan, Takahiro Hosono, Jun Yasumoto, Ko Yasumoto, Ke-Han Song, Rio Maruyama, Mariko Iijima, Mina Yasumoto-Hirose, Ryogo Takada, Kento Hijikawa, Ryuichi Shinjo

Journal of Hydrology     2023.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Effect of groundwater residence time on geogenic fluoride release into groundwater in the Mt. Meru slope area, Tanzania, the Great Rift Valley, East Africa

Shinji Nakaya, Ryogo Takada, Jun Yasumoto, Harue Masuda, Junichi Yoshitani, Ryuichi Shinjo, Innocent Lugodisha, Hans Komakech

Journal of Contaminant Hydrology ( Elsevier )    2023.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Visualization of Phosphate in Subcalicoblastic Extracellular Calcifying Medium and on a Skeleton of Coral by Using a Novel Probe, Fluorescein-4-Isothiocyanate-Labelled Alendronic Acid

Mariko Iijima, Jun Yasumoto, Kanami Mori-Yasumoto, Mina Yasumoto-Hirose, Akira Iguchi, Atsushi Suzuki, Nanami Mizusawa, Mitsuru Jimbo, Shugo Watabe & Ko Yasumoto

Marine Biotechnology ( Springer Nature )    2022.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Phosphate bound to calcareous sediments hampers skeletal development of juvenile coral

Mariko Iijima, Jun Yasumoto, Akira Iguchi, Kiyomi Koiso, Sayaka Ushigome, Natsuki Nakajima, Yuko Kunieda, Takashi Nakamura, Kazuhiko Sakai, Mina Yasumoto-Hirose, Kanami Mori-Yasumoto, Nanami Mizusawa, Haruna Amano, Atsushi Suzuki, Mitsuru Jimbo, Shugo Watabe and Ko Yasumoto

Royal Society Open Science ( Royal Society )    2021.03 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Evaluation of recharge areas of Arusha Aquifer, Northern Tanzania: Application of water isotope tracers

Innocent Lugodisha, Hans C. Komakech, Shinji Nakaya, Ryogo Takada, Junichi Yoshitani, Jun Yasumoto

Hydrology Research   51 ( 6 ) 1490 - 1505   2020.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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In Arusha urban, northern Tanzania, groundwater contributes about 80% of the water supply. However, elevated fluoride levels and evidence of anthropogenic pollution have been reported in the groundwater around Mount Meru which is a water source for Arusha urban. This study aims at understanding the recharge areas and flow pathways of groundwater in what has been a poorly monitored area. The study uses the isotopic ratio of oxygen and hydrogen to estimate the groundwater recharge area and flow pathway. The results show the recharge elevation of groundwater is between 1,800 and 3,500 m above mean sea level on the slopes of Mount Meru. The average fluoride contents in the study area are 5.3 ± 0.4 mg/L greater than the limits of 1.5 mg/L set by the World Health Organization (WHO) and Tanzania. The nitrate concentration of 83.9 mg/L at the lower elevation areas (<1,400 m above mean sea level) exceeds the 50 mg/L WHO limit. The relationship of F- with δ18O and NO3- suggests the leaching of fluoride in high altitudes and dilution in lower altitudes.

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Phosphate Enrichment Hampers Development of Juvenile Acropora digitifera Coral by Inhibiting Skeleton Formation.

Iijima M, Yasumoto K, Yasumoto J, Yasumoto-Hirose M, Kuniya N, Takeuchi R, Nozaki M, Nanba N, Nakamura T, Jimbo M, Watabe S

Marine biotechnology (New York, N.Y.) ( Marine Biotechnology )  21 ( 2 ) 291 - 300   2019.04 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Coral reef degradation due to various local stresses, such as nutrient enrichment and terrestrial run-off into coastal waters, is an increasing global concern. Inorganic phosphates have been considered to possibly inhibit skeleton formation in corals. Despite many studies available on the effects of nutrients on corals, a clear consensus on how nutrients exert deteriorative effects on corals has not been established satisfactorily. In this study, we examined the effects of phosphates and nitrates on in vitro aragonite CaCO3 formation by using biogenic polyamines and in vivo aragonite formation in the skeleton of juvenile Acropora digitifera corals. We showed that the phosphates at similar concentrations clearly inhibited both in vitro and in vivo CaCO3 formation. In contrast, nitrates inhibited neither in vitro aragonite CaCO3 formation nor in vivo aragonite formation in juvenile coral skeleton. Furthermore, our findings showed that inhibition of coral skeleton formation was due to absorption of phosphate on the skeleton, which inorganically inhibited normal development of juvenile coral skeleton.

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Atmospheric CO₂ captured by biogenic polyamines is transferred as a possible substrate to Rubisco for the carboxylation reaction.

Yasumoto K, Sakata T, Yasumoto J, Yasumoto-Hirose M, Sato SI, Mori-Yasumoto K, Jimbo M, Kusumi T, Watabe S

Scientific reports ( Scientific Reports )  8 ( 1 ) 17724   2018.12 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Biogenic polyamines are involved in a wide range of plant cellular processes, including cell division, morphogenesis and stress responses. However, the exact roles of biogenic polyamines are not well understood. We recently reported that biogenic polyamines that have multiple amino groups can react with CO2 and accelerate calcium carbonate formation in seawater. The ability of biogenic polyamines to capture atmospheric CO2 prompted us to examine their roles in photosynthesis. Here, we demonstrated that atmospheric CO2 captured by biogenic polyamines is a candidate substrate for the carboxylation reaction of ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco), which is an enzyme involved in the first major step of carbon fixation during photosynthesis, and that biogenic polyamines can accelerate the carboxylation reaction of this enzyme because of their specific affinity for CO2. Moreover, the results of our nuclear magnetic resonance (NMR) analysis showed that putrescine, which is the most common biogenic polyamine, reacts with atmospheric CO2 and promotes the formation of carbamate derivatives and bicarbonate in aqueous environments. A sufficient amount of CO2 is well known to be produced by carbonic an hydrase from bicarbonate in vivo. The present study indicates that CO2 would be also produced by the equilibrium reaction from carbonate produced by biogenic polyamines and would be used as a substrate of Rubisco, too. Our results may suggest a new photosynthetic research strategy that involves CO2-concentrating mechanisms and also possibly constitutes a potential tool for reducing atmospheric CO2 levels and, consequently, global warming.

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Hydrochemical behaviour of an underground dammed limestone aquifer in the subtropics

Nakaya Shinji, Yasumoto Jun, Ha Phan Min, Aoki Hideto, Kohara Fumiya, Masuda Harue, Masuoka Kentaroh

HYDROLOGICAL PROCESSES   32 ( 23 ) 3529 - 3546   2018.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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<jats:title>Abstract</jats:title><jats:p>In an island area with limited surface water resources, the conservation of fresh groundwater resources is important for the maintenance of the water supply and irrigation system to be used in agricultural activity. In a limestone aquifer used for irrigation on a subtropical island, the progress of the dissolution behaviour of the aquifer and the effects of CO<jats:sub>2</jats:sub> storage and chemical weathering of the aquifer must be understood to ensure sustainable groundwater use. In this study, hydrochemical behaviour of the Ryukyu limestone aquifer was investigated using the residence time of slowly flowing groundwater, which is contained by a 2.3‐km‐long underground man‐made dam constructed in 2005 located at the southern edge of Okinawa Island, Japan. Groundwater dating and horizontal flow velocity measurements indicate that the groundwater horizontal flow is slow in the underground dam area, whereas the saturation index (SI) for calcite indicates that the majority of the limestone exists in a supersaturated condition. The range of SI for gypsum was indicative of subsaturation, and the SI increased with the groundwater residence time, suggesting that the dissolution of CaSO<jats:sub>4</jats:sub> tends to proceed slowly through the common ion effect. The dissolution of CaCO<jats:sub>3</jats:sub>, however, tends to be in suspension within about a residence time of 20 years. The apparent dissolution rate of Ca in the Ryukyu limestone aquifer in this area was estimated to be approximately 2.70–4.06 nmol cm<jats:sup>−2</jats:sup> year<jats:sup>−1</jats:sup>, a value much lower than that of the early stages of the limestone dissolution. The estimated groundwater CO<jats:sub>2</jats:sub> (gas) concentrations are two order high (about 0.3–7%) relative to atmospheric CO<jats:sub>2</jats:sub> (about 0.04%), and the groundwater pH shows a tendency to decrease from 7.4 to 6.9 over the last approximately 20 years, indicating that the hydration reaction of CO<jats:sub>2</jats:sub> occurs in the Ryukyu limestone aquifer. These findings imply that high CO<jats:sub>2</jats:sub> produced in the subtropical zone is consumed slower than CO<jats:sub>2</jats:sub> production during limestone dissolution, with the exclusion of the early stage of the chemical weathering process, and causes groundwater acidification in the underground dammed limestone aquifer.</jats:p>

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琉球石灰岩帯水層における脱窒に係わる微生物相解析

安元純，廣瀬(安元)美奈，久手堅剛，宮城雄次，大城要平，聖川健斗，細野高啓，嶋田純，中野拓治

地下水学会誌 ( 公益社団法人 日本地下水学会 )  57 ( 2 ) 153 - 169   2015.05 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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本研究では，沖縄本島南部地域の琉球石灰岩帯水層において，地下水水質データと硝酸中の窒素及び酸素同位体比（δ#U15#URN#DNO#B#D3#DR#BR#DR，δ#U18#URO#DNO#B#D3#DR#BR#DR）を測定することで脱窒ポイントを推定し，PCR法を組み合わせた変性剤濃度勾配ゲル電気泳動法（以下，PCR-DGGE法）及びリアルタイムPCR等を用いた微生物相解析等を実施して，帯水層中の優占種および分離菌株の分子系統解析と脱窒関連遺伝子の検出と定量を試みると共に，その結果とδ#U15#URN#DNO#B#D3#DR#BR#DR，δ#U18#URO#DNO#B#D3#DR#BR#DRの結果を比較し，地下水中の脱窒の有無やその程度の推定に対する微生物相解析の有効性について検討した。<BR>その結果，細菌種は異なるものの，脱窒ポイント，その他のポイントに係わらず，全観測地点で脱窒能を持つと報告されている属と同じ属の細菌が検出された。リアルタイムPCRを用いて脱窒関連遺伝子（nirS/nirK）の定量を行ったところ，nirK遺伝子に比べnirS遺伝子の方が多く検出され，本地域の脱窒にはnirS遺伝子をもつ微生物が優先的にかかわっていることが明らかとなった。さらに，nirS及びnirK遺伝子のDNA コピー数とδ#U15#URN#DNO#B#D3#DR#BR#DR，δ#U18#URO#DNO#B#D3#DR#BR#DRの値との間には比較的高い相関がみられ，δ#U15#URN#DNO#B#D3#DR#BR#DR，δ#U18#URO#DNO#B#D3#DR#BR#DRを用いた同位体的手法とリアルタイムPCRを用いた脱窒関連遺伝子の定量手法を併用することが，地下水中における脱窒環境やその程度を推定する有効な手法となる可能性が示唆された。

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琉球石灰岩帯水層における広域地下水流動モデルの構築

安元純，阿部真己，中野拓治

土木学会論文集B1(水工学) ( 公益社団法人 土木学会 )  71 ( 4 ) I_217-222 - I_222   2015 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Groundwater model for understanding and predicting hydraulics and contaminant transport in aquifer make assumptions about the distribution and hydraulic properties of geologic features that may not always apply to karst aquifers. In this study, a finite difference groundwater model (MODFLOW-NWT) was applied to construct an equivalent single layer two-dimensional mathematical model of the Ryukyu limestone aquifer, which is located a southern part of Okinawa main islands. In order to handle problems at regional scale groundwater model in the aquifer, automated parameter estimation method (PEST) was used in this model. Groundwater level measurements collected in 1994 were used to calibrate a steady state model of the study area. This study shows the ability of MODFLOW-NWT and PEST to simulate regional groundwater flow in highly karstified aquifer such as Ryukyu limestone aquifer, which is important for water resource and groundwater management in the area.

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Biogenic Polyamines Capture CO2 and Accelerate Extracellular Bacterial CaCO3 Formation

Ko Yasumoto, Mina Yasumoto-Hirose, Jun Yasumoto, Ryo Murata, Shun-ichi Sato, Megumi Baba, Kanami Mori-Yasumoto, Mitsuru Jimbo, Yasukatsu Oshima, Takenori Kusumi, Shugo Watabe

Marine Biotechnology   16 ( 4 ) 465 - 474   2014 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Study on Influence of Design and Operation Factors on Effluent ATU-BOD and N-BOD Concentrations from Sedimentation Tank in Rural Sewerage Facilities

中野拓治, 安元純

農業農村工学会論文集 ( 公益社団法人 農業農村工学会 )  81 ( 283 ) 9 - 16   2013.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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The design and operation factors on the effluent ATU-BOD and N-BOD concentrations in sedimentation tank were investigated by using observed data in the rural sewerage facilities with biofilm process and activated-sludge process. The operational problems with occurrence of N-BOD were also studied on the basis of the results of BOD removal performance obtained from research data of the rural sewerage facilities with both processes. Regarding to effluent BOD concentrations in sedimentation tank with both processes, it was found that the biological nitrification reaction and nitrogenous compound had the considerable influence on the effluent N-BOD concentration in sedimentation tank. The effluent ATU-BOD concentration in sedimentation tank was assumed to be governed by first-order function with complete-mix system of biological treatment process in the rural sewerage facilities with both processes. It was recognized that the effluent ATU-BOD concentration in sedimentation tank with both processes were influenced by the design and operation factors such as influent ATU-BOD concentration, microorganisms (mixed liquor suspended solids/specific surface area of contact filter for fixed bed submerged filter), and average DO in reactor (contact aeration tank/aeration tank). The effluent ATU-BOD concentration in sedimentation tank with both processes were found to be predicted by the empirical formula of hydraulic retention time and the design/operation factors mentioned above. Consequently, it is important that the control in occurrence of N-BOD and operational countermeasure for decrease of ATU-BOD are effective to maintain BOD removal efficiency in the rural sewerage facilities with both processes.

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多変量解析を用いた石灰岩帯水層における地下水水質の統計的分類

安元純, 聖川健斗, 仲栄真史哉, 砥綿泰弘, 中野拓治

土木学会論文集 B1(水工学)(Web) ( 土木学会 )  69 ( 4 ) I.595-I.600 (J-STAGE) - 600   2013 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Multivariate statistical techniques, principal component and cluster analysis were applied to the data on groundwater quality of Limestone aquifer in the southern region of Okinawa, Japan, to extract principal factors corresponding to the different sources of variation in the hydrochemistry, with the objective of defining the main controls on the hydrochemistry at the regional scale. As a result of principal component analysis, ground water quality in the region could be classified into four principal components, that is, the groundwater is affected according to salt water and fertilizer (component 1), limestone dissolution (component 2), a redox state of a ground-water (component 3) and nitrogen accumulation/ denitrification (component 4). The cluster analysis was classified into four clusters according to the pollution situation of groundwater pollution in the study area, and the classification result was affected by season.

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地下水中硝酸性窒素濃度の時空間分布と形成要因について:― 沖縄県本島南部琉球石灰岩分布地域を例として ―

中野 拓治, 安元 純, 寺澤 春菜, 名和 規夫

農業農村工学会論文集 ( 公益社団法人 農業農村工学会 )  81 ( 4 ) 283 - 291   2013 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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琉球石灰岩分布地帯である沖縄本島南部地域地下水の硝酸性窒素について，現地観測データ等から時空間的動態を把握し，その形成要因を考察した．調査地域の硝酸性窒素は，正規確率分布によく適合しており，環境基準値（10mgL#U－1#UR）を若干超過するような濃度水準となっている．硝酸性窒素には，地下水流動に伴った上流から下流に向けた窒素負荷源が影響しているとともに，地下ダム築造で形成された地下水流動場に起因する流入・混合作用と希釈・脱窒作用が関与していることを確認できた．硝酸性窒素の経年変化には，農地からの窒素負荷による影響が示唆されるとともに，周年濃度変化には地下水位変動が影響していることを明らかにすることができた．

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連続流入間欠ばっ気活性汚泥方式の農業集落排水施設の窒素除去性能とその支配要因

中野拓治, 安元純

農業農村工学会論文集 ( 公益社団法人 農業農村工学会 )  80 ( 279 ) 253 - 260   2012.06 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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連続流入間欠ばっ気活性汚泥方式の農業集落排水施設の窒素除去性能とその支配因子について，供用中の施設から得られた観測データを用いて考察した．窒素除去性能には，硝化・脱窒工程でのばっ気槽内の酸化還元電位が大きく関与しており，安定した除去性能を確保するためには，撹拌工程においては撹拌時間，ばっ気撹拌工程ではばっ気時間・ばっ気強度の適切な設定を通じて，ばっ気撹拌終了時は酸化状態に，また，撹拌終了時には確実に還元状態となるような運転・管理条件を保つことが重要であることが確認された．また，ばっ気槽内がばっ気撹拌終了時に好気状態（ORP値で100mV程度），撹拌終了時に嫌気状態（ORP値で－50～－200mVの範囲）が確保されている条件では，窒素除去は完全混合流による1次反応に従っているとともに，窒素除去率は，ばっ気槽内のMLSS，水温，ばっ気撹拌終了時DO濃度，水理学的滞留時間を説明変数とする双曲線関数式から推定できることが示唆された．

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Submarine groundwater discharge and seawater circulation in a subterranean estuary beneath a tidal flat

Nakada Satoshi, Yasumoto Jun, Taniguchi Makoto, Ishitobi Tomonori

HYDROLOGICAL PROCESSES ( WILEY-BLACKWELL )  25 ( 17 ) 2755 - 2763   2011.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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A numerical simulation and stationary geophysical survey at Omaehama, Japan, described the hydrogeology in a tidal flat and adjacent sea water column. The simulation of a tidally influenced aquifer with inland fresh groundwater discharges showed three circulations in the subterranean tidal flat estuary: a small, tide-induced recirculation (TIR) near the sloping beach, a deeper circulation (DC) across the interface between saltwater and freshwater, and a large, tidal flat-induced circulation (TFIC) in the offshore subterranean tidal flat and slope. The horizontal distribution of the simulated submarine groundwater discharge (SGD) showed two peaks, depending on the distance from the coast along the transect line of tidal flat; the offshore peak was quantitatively consistent with the previously observed peak based on automated seepage measurements. Time-series of the observed resistivity profiles using a marine cable (140 m) showed the structure of the fresh water/salt water interface, and indicated a salt wedge intruding from the bottom aquifer and infiltration at the surface in the beach and nearshore tidal flat. The qualitative structure of the resistivity hardly changed at each tidal stage. These results qualitatively validated the circulation patterns shown by the numerical simulation. The source of this discharging groundwater in the tidal flat is a complex mixture of fresh groundwater derived from the landward aquifer, as well as locally recycled seawater, which can contribute to the purification of the nearshore seawater. Copyright (C) 2011 John Wiley & Sons, Ltd.

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有明海沿岸火山岩地域における海底湧水の湧出機構と栄養塩の輸送特性

安元純, 広城吉成, 末益大嗣, 高岡秀朋, 神野健二

水工学論文集(CD-ROM) ( 公益社団法人 土木学会 )  55 ( 4 ) ROMBUNNO.99 - I_594   2011.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Submarine Groundwater Discharge (SGD) is now recognized as a significant role to the ecology of coastal environment as well as river discharge. This paper takes a first step for highlighting nutrient transport through SGD to volcanic rock area along the Ariake Bay. SGD rates and their qualities along the coastal area of the Ariake Bay, Ohura, Saga Prefecture, Kawachi, Kumamoto Prefecture, and Fukae, Nagasaki Prefecture regions are investigated. As a result, SGD generally decreased with the distance from the shoreline except Ohura point where large seepage rate is observed. It is presumed that SGD could be classified into two types based on the rate of SGD and the geological structure. Then, it is indicated that the SGD oxidation-reduction condition varied with seepage rate and path way. The results of this study demonstrate that SGD may be considered as a significant source of nutrient to the coastal area in Ariake Bay.

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Degradation of subsurface environment due to human activities and climate variability in Asian cities

Makoto Taniguchi, Jun Shimada, Yoichi Fukuda, Makoto Yamano, Shin Ichi Onodera, Somkid Buapeng, Robert Delinom, Fernando Siringan, Chung Ho Wang, Backjin Lee, Jun Yasumoto, Keiko Yamamoto

IAHS-AISH Publication   ( 329 ) 124 - 129   2009 [ Peer Review Accepted ]

Type of publication: Research paper (international conference proceedings)

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Degradation of subsurface environments has been studied in Tokyo, Osaka, Seoul, Bangkok, Manila, Taipei and Jakarta. The groundwater temperature observed in the study cities show the magnitude of timing of surface warming due to global warming and heat island effects. Recent new techniques using remote gravity measurement and isotope data enable us to evaluate the regional scale of groundwater issues. Groundwater contaminations and accumulated materials in the subsurface environment depend on the development stage of the cities. The material transports by groundwater have been evaluated. Stable isotopes data of the groundwater and soil water can tell us me origin of the contamination and processes. Copyright © 2009 IAHS Press.

有明海沿岸域の佐賀県太良町大浦沖における海底地下水湧出と栄養塩の輸送

安元純, 広城吉成, 高岡秀朋, 古市久士, 松原英隆, 神野健二

水工学論文集(CD-ROM) ( 公益社団法人 土木学会 )  51   ROMBUNNO.81 - 486   2007.02 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Submarine Groundwater Discharge (SGD) is now recognized as an important pathway between land and sea. This paper takes a first step for estimating nutrient inputs through SGD to Ariake Bay. SGD rates and its quality along the coast of the Ariake Bay off Oura region were investigated. As a result, it was shown that on-site SGD rate ranged from 0.01 to 20.52&mu;m/s, and SGD flowed through shallow confined aquifers which consist of basalt and superposition pyroclastic fall with shorter residence time. Then, it was estimated that reduction reaction for SGD proceeded just up to denitrification, and SGD associated nutrient loads (N, P, SiO#D2#DR) are estimated at 1.40g/day, 0.07g/day, and 52.78g/day respectively. The results of this study demonstrate that SGD must be considered as a significant source of nutrient to the coastal sea area in Ariake Bay.

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Geochemical processes and their modeling at the fresh and salt water mixing zone

Kenji Jinno, Tosao Hosokawa, Yoshinari Hiroshiro, Keigo Akagi, Jun Yasumoto

Proceedings of the International Association of Hydrological Sciences, Red Books ( the International Association of Hydrological Sciences, IAHS )  320 ( 320 ) 191 - 196   2007 [ Peer Review Accepted ]

Type of publication: Research paper (international conference proceedings)

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Oxidation-reduction geochemical processes coupled with mass transport in a coastal aquifer is a unique subsurface environmental phenomenon to model. When a porous material is contaminated by organic carbons, nitrate is denitrified and manganese dioxide and oxi-iron hydroxide would be reduced. However, it is expected that the reduced divalent iron is oxidized once again by seawater when discharged to the sea. The paper discusses a numerical model of transport and geochemical reaction processes along the mixing zone of fresh and reduced salt water in a coastal aquifer. By comparing the numerical solution with experimental observations for the precipitation of divalent iron along the mixing zone, the validity of the model is demonstrated. Copyright © 2008 IAHS Press.

Relation between the depth of saltwater/freshwater interface estimated by Wenner method and the electric conductivity of groundwater

大年邦雄, 安元純, 藤原拓

地下水学会誌 ( 地下水学会誌 )  48 ( 3 ) 169 - 181   2006.08 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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It is known that electrical methods for s u rface geophysical survey might be capable to locate saline water in a coastal unconfined aquifer. This is the result of the increase in bulk conductivity with increasing in pore water conductivity. The relation between the depth of saltwater intrusion estimated by electrical method and the electric conductivity (EC) of pore water corresponding to its depth, however, is not verified quantitatively. This study revealed the quantitative relation that the estimated depth by Wenner method corresponds to EC of 3 mS/cm (Cl#U-#UR = 450 mg/l) of groundwater. Considering that such depth is the upper part of the mixing zone, electrical method will be the powerful measure for monitoring the saltwater intrusion in a wide farming area along the coast.

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感潮河川周辺域の不圧帯水層における塩水侵入の変動特性

安元純, 上荒磯聡, 六車麗子, 藤原拓, 大年邦雄

水工学論文集(CD-ROM) ( 公益社団法人 土木学会 )  50   ROMBUNNO.043 - 258   2006 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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Salt water intrusion in a coastal aquifer varies corresponding to the sea level and rainfalls. The influence of tidal river might be added to the behavior of salt water intrusion when the aquifer locates near the tidal river. Consequently it is easy to understand that the behavior of salt water bodies in such a situation will be quite complicated. The present study describes the findings about the salt water intrusion on the basis of the long-term field measurements conducted near a tidal river. Following findings were obtained: 1) The interface of fresh-salt water bodies in an aquifer consists of a wide mixing zone. 2) The depth of mixing zone varies cyclically and more largely during a spring tide than a neap tide. 3) Rainfalls may have the possibility to uplift the upper mixing zone remarkably for a short period after the rainfall event. Such possibility has to be verified in the future.

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海岸帯水層における塩水侵入深の時間変動特性に及ぼす感潮河川の影響

安元純, 芝洋輔, 藤原拓, 大年邦雄

地下水学会誌 ( 地下水学会誌 )  46 ( 4 ) 299 - 313   2004.11 [ Peer Review Accepted ]

Type of publication: Research paper (scientific journal)

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河川感潮域においては,潮汐に伴う海面および感潮河川の水位変動が海岸帯水層への塩水侵入の時空間変動特性に影響を及ぼしていると考えられる.しかし,これらの要因を定量的に分離するのは通常の調査では困難である.本研究では,河口水門を閉じて感潮河川の水位を一定時間固定し,そのことが地下水への塩水侵入に及ぼす影響を観測により検討した.河川水位の固定化に伴って地下水位および淡塩境界の変動が抑制されること,河川近傍ほど抑制程度の大きいことがわかった.また,淡塩境界面モデルを用いた数値計算により観測結果を検証するとともに,河川水位を固定する時間長と地下水への影響持続時間長との関係について検討した.

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