Assistant Professor

Research Fields, Keywords


Graduating School 【 display / non-display


    Iwate University   Faculty of Engineering   Department of Civil and Environmental Engineering   Graduated

Graduate School 【 display / non-display


    Tohoku University  Graduate School, Division of Engineering  Department of Civil and Environmental Engineering  Doctor's Course  Completed

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  • Tohoku University -  Doctor (Engineering)


Research Career 【 display / non-display

  • Evaluating riverine environment using a hydrological model

    Cooperative Research  

    Project Year: 2010.04  -   

Papers 【 display / non-display

  • Projection of invertebrate populations in the headwater streams of a temperate catchment under a changing climate

    Nukazawa K., Arai R., Kazama S., Takemon Y.

    Science of the Total Environment   642   610 - 618   2018.11  [Refereed]

    Joint Work

     View Summary

    Climate change places considerable stress on riverine ecosystems by altering flow regimes and increasing water temperature. This study evaluated how water temperature increases under climate change scenarios will affect stream invertebrates in pristine headwater streams. The studied headwater-stream sites were distributed within a temperate catchment of Japan and had similar hydraulic-geographical conditions, but were subject to varying temperature conditions due to altitudinal differences (100 to 850 m). We adopted eight general circulation models (GCMs) to project air temperature under conservative (RCP2.6), intermediate (RCP4.5), and extreme climate scenarios (RCP8.5) during the near (2031–2050) and far (2081–2100) future. Using the water temperature of headwater streams computed by a distributed hydrological-thermal model as a predictor variable, we projected the population density of stream invertebrates in the future scenarios based on generalized linear models. The mean decrease in the temporally averaged population density of Plecoptera was 61.3% among the GCMs, even under RCP2.6 in the near future, whereas density deteriorated even further (90.7%) under RCP8.5 in the far future. Trichoptera density was also projected to greatly deteriorate under RCP8.5 in the far future. We defined taxa that exhibited temperature-sensitive declines under climate change as cold stenotherms and found that most Plecoptera taxa were cold stenotherms in comparison to other orders. Specifically, the taxonomic families that only distribute in Palearctic realm (e.g., Megarcys ochracea and Scopura longa) were selectively assigned, suggesting that Plecoptera family with its restricted distribution in the Palearctic might be a sensitive indicator of climate change. Plecoptera and Trichoptera populations in the headwaters are expected/anticipated to decrease over the considerable geographical range of the catchment, even under the RCP2.6 in the near future. Given headwater invertebrates play important roles in streams, such as contributing to watershed productivity, our results provide useful information for managing streams at the catchment-level.


  • Simulating the Advection and Degradation of the Environmental DNA of Common Carp along a River

    Nukazawa K., Hamasuna Y., Suzuki Y.

    Environmental Science and Technology   52   10562 - 10570   2018.09  [Refereed]

    Joint Work

     View Summary

    The environmental DNA (eDNA) method is a novel technique for precise and efficient biological surveillance. Although eDNA has been widely used to monitor various freshwater organisms, eDNA dynamics in streams remain poorly understood. In this study, we investigated the eDNA dynamics of common carp (Cyprinus carpio) in a forested headwater stream affected by the effluent from a carp farm. We evaluated the longitudinal variation in carp eDNA along a river downstream from the farm and performed a temporal eDNA decay experiment using digital polymerase chain reaction. On the basis of the resulting decay constants, we built a model to simulate the advection and degradation of eDNA along the studied river. The observed eDNA flux (concentration multiplied by flow rate) decreased exponentially with distance downstream from the farm, and eDNA was detected 3 km downstream of the farm. Although the water temperatures were similar, the eDNA decay constant was lower in autumn than in summer. The simulated eDNA concentration was markedly larger (>10 times) than the observed concentration, suggesting that eDNA removal is accelerated in the stream environment compared to in conventional experimental settings.


  • Investigation of <i><b>Escherichia coli</b></i> in Urban Steam with Inflow of Treated Wastewater

    SUZUKI Yoshihiro, NISHIYAMA Masateru, NUKAZAWA Kei, ISHII Satoshi

    Journal of Japan Society on Water Environment   41   19 - 26   2018.02  [Refereed]

    Joint Work

     View Summary

    <p>There is growing concern for the applicability of <i>Escherichia</i> <i>coli</i> as a fecal indicator bacterium in the water environment because <i>E.</i> <i>coli</i> has been reported to regrow in a variety of environments. We investigated longitudinal variation in <i>E.</i> <i>coli</i> counts along a small channel which receives the effluent of treated wastewater. The two fecal indicator bacteria, <i>E.</i> <i>coli</i> and Enterococci, were enumerated, and these bacterial fluxes were calculated from bacteria counts and river flow. As a result, the flux of <i>E.</i> <i>coli</i> was larger downstream of the effluent site than the sum of the fluxes upstream and in the effluent. A high <i>E.</i> <i>coli</i> count was detected in the riverbed sediment of a downstream site. In addition, pulsed-field gel electrophoresis revealed that the genotypes of <i>E.</i> <i>coli</i> isolated from the upstream water, periphyton, and riverbed sediment samples were concordant (similarity = 1.0) . These results indicate that <i>E.</i> <i>coli</i> survived and accumulated in riverbed periphyton and sediment and that <i>E.</i> <i>coli</i> may regrow in a small stream that is strongly affected by treated wastewater. When we assess the fecal pollution in rivers, it is necessary to consider the possibility of <i>E.</i> <i>coli</i> regrowth.</p>

    DOI CiNii

  • Negligible contribution of reservoir dams to organic and inorganic transports in the lower Mimi River, Japan

    Nukazawa K., Kihara K., Suzuki Y.

    Journal of Hydrology   555   288 - 297   2017.12  [Refereed]

    Joint Work

     View Summary

    Rivers fulfill an essential ecological role by forming networks for material transport from upland forests to coastal areas. The way in which dams affect the organic and inorganic cycles in such systems is not well understood. Herein, we investigated the longitudinal profiles of the various components of the water chemistry across three cascade dams in Japan: the Yamasubaru Dam, Saigou Dam, and Ohuchibaru Dam, which are situated along the sediment-productive Mimi River in different flow conditions. We analyzed the following water quality components: suspended solids (SS), turbidity, total iron (TFe), dissolved iron (DFe), total organic carbon (TOC), total nitrogen (TN), total phosphorus (TP), humic substance (HS), and major ionic components (Na+, Mg2+, Ca2+, Cl−, NO3−, and SO42−) in the downstream channels of the three dams during the low–intermediate-flow and high-flow events from 2012 to 2014. We estimated hourly loads of each component using hourly turbidity data and discharge data (i.e., L–Q model) separately, and the results are integrated to estimate the annual fluxes. The annual fluxes between the methods were compared to verify predictability of the conventional L–Q models. Annual flux of TOC, TN, DFe, and HS estimated by the turbidity displayed similar values, whereas the flux of SS, TFe, and TP tended to increase downstream of the dams. Among the dams, estimated flux proportions for TP and TFe were higher during high-flow events (74%–94%). Considering geographic conditions (e.g., absence of major tributary between the dams), the result implies that accumulated TP and TFe in the reservoirs may be flushed and transported downstream with SS over the short height dams during flood events. Assuming this process, the reservoir dams probably make only a fractional contribution to the organic and inorganic transport in the catchment studied. The percent flux errors for SS, TFe, and TP fluxes ranged from −7.2% to −97% (except for the TP flux in 2013), which highlights the risk of underestimating these components when using an L–Q model.



    Kengo Watanabe, So Kazama, Shunsuke Aita, Kei Nukazawa

      73   I_1153 - I_1158   2017.03  [Refereed]

    Joint Work

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Presentations 【 display / non-display

  • Effect on sand supply to foreshore by beach nourishment on the Miyazaki Coast

    Miyazono, A., Ito, K., Nukazawa, K., Mitsuteru, I., Suzuki, Y.

    水環境技術会議  2018.07  -  2018.07 

  • Development of High Efficiency Concentration Method of DNA from River Water by Combined Process of Coagulation and Form Separation

    Jikumaru, A., Imafuku, Y., Teranishi, K., Nukazawa, K., Ogura, Y., Suzuki, Y.

    水環境技術会議  2018.07  -  2018.07 

  • Comparison of Antibiotic-Resistant Escherichia coli Collected from Uninhabited Island and Urban Ponds in Miyazaki, Japan

    Nishimura, E., Sugita, K., Sakamoto, S., Nukazawa, K., Suzuki, Y.

    水環境技術会議  2018.07  -  2018.07 

  • Catchment-scaled species diversity modeling of stream invertebrates using a hydrological simulation

    Nukazawa, K., Kazama, S., Watanabe, K.

    HydroEco2017  2017.06  -  2017.06 

  • Adaptive genetic consequences of climate change for stream insects: a hydrothermal simulation approach

    Nukazawa K, Kazama S, Watanabe K

    第20回国際水理学会アジア太平洋地域会議  2016.08  -  2016.08  International Association for Hydro-Environment Engineering and Research (IAHR)

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