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Affiliation |
Engineering educational research section Civil and Environmental Engineering Program |
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Title |
Associate Professor |
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Related SDGs |
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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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Spatial distribution and loads of nutrients in the Hitotsuse Dam reservoir, Japan Reviewed
Nukazawa Kei, Fujii Naoto, Miura Naoto, Suzuki Yoshihiro
Inland Waters 16 ( 1 ) 2578945 2026.3
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：Informa UK Limited
Eutrophication and harmful algal blooms (HABs) are triggered by complex and intrinsic factors in lakes, reservoirs, and watersheds. Therefore, to better understand their mechanisms, the comprehensive monitoring of lakes/reservoirs and inflowing rivers is a primary challenge. We investigated the spatial trends of water quality components related to algal blooms, such as nitrogen (N) and chlorophyll a, in the Hitotsuse Dam reservoir in southwest Japan and inferred their input or output loads in the reservoir. The water quality components (N, phosphorus [P], and chlorophyll a) were measured at 142 sites in the reservoir and inflowing rivers once a year from 2018 to 2020. Additionally, nonlinear regression models were developed to determine the balance of N and P loads in the reservoir. Around the aquaculture rafts in the reservoir, higher concentrations of nitrate-N and total N (TN) were observed, suggesting that the water quality of the reservoir surface water was affected by aquaculture. The TN and TP loads in the effluent were almost equivalent to the total loads of the dam reservoir, which comprised the inflow, aquaculture, and substrate loads. The study demonstrated that evaluating the water quality patterns is useful for identifying the causes of HABs and determining areas where such algal blooms tend to emerge.
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Xu Chen, Nukazawa Kei
PeerJ 13 e20166 2025.10
Authorship：Last author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：PeerJ
Recent developments in environmental DNA (eDNA) analyses have facilitated non-invasive and cost-effective ecological monitoring. Based on eDNA of terrestrial species released into water upon contact, simultaneous detection of aquatic and terrestrial species is feasible. However, an efficient sampling design for terrestrial vertebrate eDNA in aquatic environments has not yet been established because DNA is rarely released into these environments. In this study, we targeted eDNA transported from land to rivers through surface runoff during rainfall in three rivers and one irrigation channel within the Kiyotake River system, Japan. We quantified the eDNA concentration of a specific terrestrial vertebrate (Bos taurus) using digital polymerase chain reaction (PCR) and examined the efficiency of using filter papers with different pore sizes (0.7 µm and 2.7 µm). We also assessed the influence of various environmental factors (e.g., rainfall characteristics described by the parameters of Gaussian distribution, water turbidity) on eDNA detection across different rainfall events. During the surveys, target DNA was detected in 42 out of 47 samples, suggesting the feasibility of consistently detecting terrestrial mammals from stormwater runoff. Overall, compared with the glass fiber filter with larger pore size, the smaller pore size filter captured more eDNA. The generalized linear mixed model revealed that prolonged rainfall duration, turbidity, and pH had a significant positive effect on eDNA concentration, whereas the distance from the assumed point of entry into the river to the sampling point had a significant negative effect. These results suggest that the runoff and transport of eDNA from terrestrial areas to rivers are enhanced under prolonged rainfall conditions, although eDNA degrades while transported along a longer watercourse by biochemical decomposition and sedimentation.
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Nukazawa Kei, Tanaka Ryo, Mineda Haruki
Ecology and Evolution 15 ( 10 ) e72411 2025.10
Authorship：Lead author, Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：British Ecological Society
Habitat models that can predict the habitat suitability for riverine organisms and their distribution along environmental gradients are helpful in watershed environmental management. However, the impacts of dams on riverine communities and their habitats have not yet been considered in such models, although dams have considerably altered important riverine habitats. In this study, we aim to develop catchment-scale habitat models of macroinvertebrate communities with predictor variables characterizing the impacts of dams. We studied the Omaru River catchment in southwest Japan, where the river flow has been altered considerably because of multiple hydropower dams. Multiple machine learning techniques, such as XGBoost and LightGBM were used to model the habitat distributions of 170 macroinvertebrate taxa observed throughout the river catchment. We used predictor variables of dam impacts derived based on geographical information system data (hereafter, dam metrics) and physically simulated flow data using a hydrological model. Among the modeling techniques, gradient boosting algorithms (XGBoost and LightGBM) with optimized tree number parameters exhibited the highest mean accuracy among the analyzed taxa, followed by the random forest algorithm. The accuracy of the habitat models for the macroinvertebrate community and habitat groups considerably improved with the integration of dam metrics and flow predictors. Of the habit groups considered, clingers showed a keen response to low-flow metrics, presumably owing to flow alteration caused by the studied dams, as the downstream sections of these dams received only residual flow. Our findings indicate that (1) variables of dam impacts greatly improve the predictive capability of macroinvertebrates and (2) gradient boosting machines with optimized parameters are favorable for habitat modeling of the biotic community. Our models are helpful when river practitioners implement conservation measures as they better understand the environmental consequences of their flood prot
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ASSESSING RESPONSE OF ENVIRONMENTAL FLOW TO LAND COVER CHANGES USING A DISTRIBUTED HYDROLOGICAL MODEL Reviewed
NUKAZAWA Kei, KURAYAMA Chiho, INOUE Yuki
Japanese Journal of JSCE 81 ( 27 ) n/a 2025.9
Authorship：Lead author, Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers
There are few studies that have evaluated the spatial pattern of streamflow alteration considering environmental aspects due to land use changes over an entire watershed. In this study, a distributed runoff model was applied to the Omaru River and Oyodo River watersheds in Miyazaki Prefecture, Japan, and evaluated changes in flow regime by 1) comparing model analyses with past (1991) and present (2021) land use, and 2) using model analyses with infiltration parameter changes based on simple watershed action scenarios. In the first attempt, it was confirmed that broader forested and urbanized areas contributed to increase and decrease in low flows, respectively. In the second analyses, an increasing trend in winter discharge under the high-infiltration scenario was observed in catchments where forests are located in the downstream area or where the forest cover ratio is high. Altered natural flow regime caused by land use change may trigger a wide-ranging effect on the river ecosystem.
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EVALUATION OF ENVIRONMENTAL DNA VARIATION FOR TURBID WATER CONSIDERING DNA STATES Reviewed
MIKAMI Yuki, XU Chen, NUKAZAWA Kei
Japanese Journal of JSCE 80 ( 25 ) n/a 2024.11
Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers
Although the accuracy of environmental DNA (eDNA) detection is influenced by biological and environmental conditions, eDNA dynamics in turbid water is not well understood, precluding establishment of eDNA surveys in turbid water area. In this study, we evaluated the effect of different turbidity conditions on aqueous eDNA fate with different states. Water samples under five turbidity conditions (0, 20, 50, 100, and 200 ppm) were designed by mixing riverbed sediment and either distilled water or aquarium water rearing common carps (<i>Cyprinus carpio</i>). We filtered the turbid water samples using two types of glass fiber filters with different pore sizes and quantified carp eDNA using digital PCR. Consequently, as turbidity increased, the concentration of eDNA also increased; however, under high turbidity conditions, the eDNA concentration tended to decrease. These findings suggest that eDNA recovery is higher at moderate levels of turbidity owing to the adsorption of eDNA and the influence of PCR inhibitors.
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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濁水を対象とした新規現地濃縮法QuickConcによる環境DNA回収の検討
徳永 優⽃・三上 優貴・Xu Chen・糠澤 桂
令和7年度 土木学会西部支部研究発表会
Event date： 2026.3.7
Presentation type：Oral presentation (general)
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宮崎県耳川における3ダム連携通砂に対する底生動物群集の中期的応答
松尾 圭祐, 糠澤桂
令和7年度 土木学会西部支部研究発表会
Event date： 2026.3.7
Presentation type：Oral presentation (general)
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降雨時に河川へ流出する環境DNAの分析に基づく水・陸生種の検出条件の検討
Xu Chen, 糠澤桂
応用生態工学会九州地区会令和7年度九州地区事例・研究発表会
Event date： 2026.1.19
Presentation type：Oral presentation (general)
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濁水条件下の環境DNA回収における新規現地濃縮法QuickConcの有用性評価 International conference
Xu Chen, 徳永 優⽃, 三上 優貴, 糠澤桂
第8回環境DNA学会山口大会
Event date： 2025.12.10 - 2025.12.13
Presentation type：Poster presentation
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宮崎県清武川水系における環境DNA移流モデルと流量データを用いた河川生物量推定手法の検討 International conference
野崎康平，三上優貴，Xu Chen，糠澤桂
第8回環境DNA学会山口大会
Event date： 2025.12.10 - 2025.12.13
Presentation type：Poster presentation
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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流域環境管理と防疫調査を繋ぐ河川-河畔生物一斉調査手法の開発
Grant number：25K00041 2025.04 - 2029.03
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(B)
Authorship：Principal investigator
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水生昆虫群集が発現する機能的多様性を指標とする河川の生息場構造の最適化
Grant number：25H01201 2025.04 - 2029.03
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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タイ国の大気降下物によるアシッドショックが水環境に与えるリスクの定量評価
Grant number：24KK0086 2024.04 - 2028.03
独立行政法人日本学術振興会 科学研究費基金 国際共同研究加速基金（海外連携研究）
Authorship：Coinvestigator(s)
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AdMitにおける河川植生伐採のマルアダプテーション回避の定量評価
Grant number：24H00329 2024.04 - 2028.03
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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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)
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