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Affiliation |
Engineering educational research section Department of Civil and Environmental Engineerring Program |
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Associate Professor |
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External Link |
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NUKAZAWA Kei
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Degree 【 display / non-display 】
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Doctor (Engineering) ( 2013.3 Tohoku University )
Research Areas 【 display / non-display 】
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Social Infrastructure (Civil Engineering, Architecture, Disaster Prevention) / Hydroengineering
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Environmental Science/Agriculture Science / Environmental dynamic analysis
Papers 【 display / non-display 】
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Ito K., Matsunaga M., Itakiyo T., Oishi H., Nukazawa K., Irie M., Suzuki Y.
International Journal of Sediment Research 2023.6
Language：English Publishing type：Research paper (scientific journal) Publisher：International Journal of Sediment Research
Sediment causes a serious problem in relation to dam function. A cooperative sediment sluicing operation has been under way since 2017 to prevent sediment from accumulating in dams in the Mimi River, Miyazaki, Japan. To achieve a smooth and stable operation, it is very important to determine the sediment source and a sediment transport system to maintain the dam's function. In the current study, the source and transport of sediment from the Mimi River basin have been analyzed with X-ray diffraction (XRD) to reveal the peaks of mineral species. The sediment samples were collected in the Mimi River basin from the Tsukabaru Dam to the sea in an area including 4 dams and 5 tributaries. In addition, the minerals in samples collected in 2014, before the start of the sediment sluicing operation, and from 2018 to 2020, after the start of the operation, were analyzed. An evaluation of the similarity of the sediment at each sampling point based on the X-ray diffraction peaks of mineral species showed that sediment distributed upstream was transported downstream in the year when the sediment sluicing was done. This result indicates that the sediment sluicing operation at dams ensured the continuity of the sediment distribution in the Mimi River basin. In addition, an investigation done in 2020 showed that sediment particles very similar to those of the upstream tributaries were deposited downstream because of extensive flooding caused by a large typhoon. The management of sediment transport has the greatest importance in a river basin where a dam is to be constructed. It is possible to trace the history of the sediment distribution and movement resulting from the operation of sediment sluicing by using sediment mineral analysis.
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Xie H., Yamada K., Tamai S., Shimamoto H., Nukazawa K., Suzuki Y.
Environmental Science and Pollution Research 2023.6
Language：English Publishing type：Research paper (scientific journal) Publisher：Environmental Science and Pollution Research
Antibiotic-resistant bacteria (ARBs) can now be detected not only in clinical institutions but also in wastewater treatment plants (WWTPs), extending the range of emergence to residential areas. In this study, we investigated the change of antibiotic-resistant Escherichia coli (E. coli) and other coliforms in each treatment process at WWTPs. Throughout the treatment process, the numbers of E. coli and other coliforms were significantly reduced to less than 5.7 ± 0.5 CFU/100 ml and 2.4 ± 0.0×102 CFU/100 ml, respectively. However, ESBL-producing E. coli and other coliforms were detected in each treatment process (even after chlorination) at 5.6% and 4.8%, compared to the total E. coli and other coliforms counts. Then, ESBL-producing-related genes were identified via PCR analyses, and the most predominant gene was CTX-M-9 in both E. coli (47.2%) and other coliforms (47.3%). Although actual WWTPs greatly reduced the number of bacteria, the relative prevalence of ESBL-producing bacteria was increased, suggesting that ESBL-producing bacteria remain in the effluent at minimal concentrations and could be diffusing to water bodies.
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Contrasting adaptive genetic consequences of stream insects under changing climate Reviewed International coauthorship
Nukazawa K., Chiu M-C., Kazama S., Watanabe K.
Science of the Total Environment 872 162258 2023.5
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Science of the Total Environment
Freshwater biodiversity undergoes degradation due to climate change. Researchers have inferred the effects of climate change on neutral genetic diversity, assuming the fixed spatial distributions of alleles. However, the adaptive genetic evolution of populations that may change the spatial distribution of allele frequencies along environmental gradients (i.e., evolutionary rescue) have largely been overlooked. We developed a modeling approach that projects the comparatively adaptive and neutral genetic diversities of four stream insects, using empirical neutral/ putative adaptive loci, ecological niche models (ENMs), and a distributed hydrological-thermal simulation at a temperate catchment under climate change. The hydrothermal model was used to generate hydraulic and thermal variables (e.g., annual current velocity and water temperature) at the present and the climatic change conditions, projected based on the eight general circulation models and the three representative concentration pathways scenarios for the two future periods (2031–2050, near future; 2081–2100, far future). The hydraulic and thermal variables were used for predictor variables of the ENMs and adaptive genetic modeling based on machine learning approaches. The increases in annual water temperature in the near- (+0.3–0.7 °C) and far-future (+0.4–3.2 °C) were projected. Of the studied species, with different ecologies and habitat ranges, Ephemera japonica (Ephemeroptera) was projected to lose rear-edge habitats (i.e., downstream) but retain the adaptive genetic diversity owing to evolutionary rescue. In contrast, the habitat range of the upstream-dwelling Hydropsyche albicephala (Trichoptera) was found to remarkably decline, resulting in decreases in the watershed genetic diversity. While the other two Trichoptera species expanded their habitat ranges, the genetic structures were homogenized over the watershed and experienced moderate decreases in gamma diversity. The findings emphasize the evolutionary rescue potential, depending on the extent of species-specific local adaptation.
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Tamai S., Ogura Y., Okuno M., Nukazawa K., Suzuki Y.
Environmental Science: Water Research and Technology 2023.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Environmental Science: Water Research and Technology
Dissolved free extracellular DNA (exDNA), DNA released outside the cell, is present in aquatic environments at very low concentrations. Additionally, exDNA passes through a 0.22 μm filter, making it difficult to capture for analysis. Thus, information on exDNA is scarce, and the composition of genes present in exDNA is unknown. In this study, we developed a process for highly concentrating exDNA adsorbed on colloids and then dissolving the colloids with an acid using colloidal adsorption and foam concentration. After applying this strategy, 66.3% ± 3.3% of the uidA gene and 39.4% ± 2.4% of the tetA gene were recovered from genomic DNA carrying the uidA gene and plasmids carrying the tetA gene (n = 3), respectively. Using the developed method, 1000 mL of effluent of a wastewater treatment plant was concentrated to 400 μL, and exDNA was rapidly recovered at a high concentration (concentration ratio: 2500×). Furthermore, metagenomic analysis revealed the function of some exDNA genes, such as those encoding antibiotic resistance proteins. The information revealed in this study contributes to the elucidation of the mechanisms of horizontal gene transfer in aquatic environments.
DOI： 10.1039/d3ew00015j
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Tamai S., Shimamoto H., Nukazawa K., Suzuki Y.
Microorganisms 11 ( 4 ) 2023.4
Language：English Publishing type：Research paper (scientific journal) Publisher：Microorganisms
High counts of bacteria are present in beach sand, and human health threats attributable to contact with sand have been reported. In this study, we investigated fecal indicator bacteria in the top surface sand of coastal beaches. Monitoring investigations were performed during a monsoon when rainfall occurs randomly, and the composition of the coliforms was analyzed. The coliform count in the top surface sand (depth < 1 cm) increased by approximately 100 fold (26–2.23 × 103 CFU/100 g) with increasing water content because of precipitation. The composition of the coliforms in the top surface sand changed within 24 h of rainfall, with Enterobacter comprising more than 40% of the coliforms. Estimation of factors that changed the bacterial counts and composition revealed that coliform counts tended to increase with increasing water content in the top surface sand. However, the abundance of Enterobacter was independent of the sand surface temperature and water content. Coliform counts in the top surface sand rapidly increased and the composition showed remarkable variations because of the supply of water to the beach following rainfall. Among them, some bacteria with suspected pathogenicity were present. Controlling bacteria in coastal beaches is important for improving public health for beachgoers.
Books 【 display / non-display 】
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宮崎県一ツ瀬川における濁水長期化 ～その原因と産官学民が連携した対策～
杉尾哲, 糠澤桂, 鈴木祥広（ Role： Edit）
パブフル 2022.2
Book type：Scholarly book
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風間 聡, 小森 大輔, 峠 嘉哉, 糠澤 桂, 横尾 善之, 渡辺 一也（ Role： Contributor）
理工図書 2020.9 （ ISBN:9784844608844 ）
MISC 【 display / non-display 】
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ダム堆砂対策による河川生態系の応答に関する事例紹介 Invited
糠澤桂，鈴木祥広
電力土木 2020.1
Language：Japanese Publishing type：Article, review, commentary, editorial, etc. (scientific journal)
Presentations 【 display / non-display 】
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ダムの影響を考慮した機械学習による河川生物分布モデルの構築
田中凌央，糠澤桂
2022年度日本水環境学会九州沖縄支部研究発表会
Event date： 2023.3.2
Language：Japanese Presentation type：Oral presentation (general)
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降雨時における環境DNAによる陸生種検出とその影響要因の検討
Xu Chen，糠澤桂
2022年度日本水環境学会九州沖縄支部研究発表会
Event date： 2023.3.2
Language：Japanese Presentation type：Oral presentation (general)
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宮崎県小丸川水系における環境DNAを用いた魚類存在量の評価
樋口公大，糠澤桂
2022年度日本水環境学会九州沖縄支部研究発表会
Event date： 2023.3.2
Language：Japanese Presentation type：Oral presentation (general)
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分布型流出モデルを用いた宮崎県内流域における過去40年間の流況変化の評価
井上優希，峯田陽生，糠澤桂
2022年度日本水環境学会九州沖縄支部研究発表会
Event date： 2023.3.2
Language：Japanese Presentation type：Oral presentation (general)
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分布型流出モデルを用いた低流量期間における広域水文水理量の推定
峯田陽生，糠澤桂
2022年度日本水環境学会九州沖縄支部研究発表会
Event date： 2023.3.2
Language：Japanese Presentation type：Oral presentation (general)
Awards 【 display / non-display 】
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ELR2022つくば 優秀ポスター発表賞
2022.9 日本緑化工学会、日本景観生態学会、応用生態工学会
田中凌央，糠澤桂，鈴木祥広
Award type：Award from Japanese society, conference, symposium, etc. Country：Japan
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第55回環境工学研究フォーラム 優秀ポスター発表賞
2018.12 土木学会
西村恵美，糠澤桂，鈴木祥広
Award type：Award from Japanese society, conference, symposium, etc. Country：Japan
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応用生態工学会第22回研究発表会 優秀ポスター研究発表賞
2018.9 応用生態工学会
糠澤桂
Award type：Award from Japanese society, conference, symposium, etc. Country：Japan
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平成28年度建設工学研究奨励賞
2017.6 一般財団法人建設工学研究振興会 宮崎における分布型汚濁流出モデルの開発とその利用による河川環境・生物多様性評価
糠澤桂
Award type：International academic award (Japan or overseas) Country：Japan
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第21回地球環境シンポジウム 優秀講演賞
2014.9 土木学会地球環境委員会
糠澤桂, 風間聡, 渡辺幸三
Award type：Award from Japanese society, conference, symposium, etc. Country：Japan
Grant-in-Aid for Scientific Research 【 display / non-display 】
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人口減少下での中小河川の水文・環境変化と新しい管理手法の研究
Grant number：20H00256 2020.04 - 2024.03
独立行政法人日本学術振興会 科学研究費補助金 基盤研究(A)
Authorship：Coinvestigator(s)
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蚊共生細菌ボルバキアによるデング熱の生態学的制御：安心・安価な新技術の提案
Grant number：19KK0107 2019.10 - 2022.03
独立行政法人日本学術振興会 科学研究費補助金 国際共同研究加速基金（国際共同研究強化(Ｂ))
Authorship：Coinvestigator(s)
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Eco-epidemiology of Dengue Mosquitoes in Bandung, Indonesia in Relation to Viral Tra nsmission and Climate Change
2019.04 - 2022.03
Grant-in-Aid for Scientific Research
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流出解析に基づく流域一貫の河川生息場モデルの高度化: 流況と空間解像度に着目して
Grant number：19K15101 2019.04 - 2022.03
科学研究費補助金 若手研究
Authorship：Principal investigator
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健全な流砂系の回復によるサステナブル流域総合土砂管理の実証研究
2017.04 - 2020.03
科学研究費補助金 基盤研究(B)
Authorship：Coinvestigator(s)
Available Technology 【 display / non-display 】
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河川への人為負荷が生態系に与える影響の評価
水文シミュレーションによる気候変動下の流域環境評価
環境DNAの動態評価Home Page： 糠澤桂のウェブページ
Related fields where technical consultation is available：・数値解析による水文流出過程の計算
・生息環境の定量的評価方法
・河川環境調査 ・気候変動解析Message：・今後の研究計画①：耳川流域におけるダム通砂に伴う河川生態系のレスポンス評価
・今後の研究計画②：宮崎県の河川における治水・環境評価モデルの構築
・今後の研究計画③：環境DNAの動態評価研究