Publications by authors named "So Kazama"

Article Synopsis
  • - Water quality issues are increasingly problematic in developing countries like Sri Lanka, with large data from monitoring programs complicating effective analysis and interpretation of water pollution across the Kelani River.
  • - The study utilized latent variable and machine learning techniques to analyze 17 water quality parameters from 2016 to 2020, identifying 10 key factors influencing water quality variations and accounting for 77% of total data variance.
  • - Findings revealed that areas near industrial zones had higher pollution, seasonal variations in water quality were tied to rainfall, and a latent variable approach could help authorities better manage water quality challenges.
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Land subsidence in Bangkok, a pressing environmental challenge, demands sustained long-term policy interventions. Although mitigation measures have successfully alleviated subsidence rates within inner Bangkok, neighboring provinces continue to experience escalating rates. Conventional land-based monitoring methods exhibit limitations in coverage, and the anticipated nonlinear contributions of climatic and socioeconomic factors further complicate the spatiotemporal distribution of subsidence.

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Article Synopsis
  • - Freshwater biodiversity is facing threats from climate change, affecting the genetic diversity of stream insect populations, and previous research often overlooked how species adapt to changing environments (evolutionary rescue).
  • - A new modeling approach was developed to analyze both adaptive and neutral genetic diversities of four stream insect species, taking into account environmental changes influenced by climate models and simulations of hydrological and thermal conditions.
  • - Results indicate that some species, like Ephemera japonica, may retain genetic diversity while losing habitat, whereas others, such as Hydropsyche albicephala, face significant habitat loss and reduced genetic diversity, highlighting different adaptive responses among species in response to climate change.
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Environmental DNA (eDNA) analysis provides an efficient and objective approach for monitoring and assessing ecological status; however, studies on the eDNA of aquatic insects, such as Ephemeroptera, Plecoptera, and Trichoptera (EPT), are limited despite its potential as a useful indicator of river health. Here, we investigated the community structures of aquatic insects using eDNA and evaluated the applicability of eDNA data for calculating assessment indices. Field surveys were conducted to sample river water for eDNA at six locations from upstream to downstream of two rivers in Japan in July and November 2016.

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Selecting a proper spatial resolution for urban rainfall runoff modeling was not a trivial issue because it could affect the model outputs. Recently, the development of remote sensing technology and increasingly available data source had enabled rainfall runoff process to be modeled at detailed and microscales. However, the models with less complexity might have equally good performance with less model establishment and computation time.

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Article Synopsis
  • Dietary carbon sources in headwater streams are divided into allochthonous (imported) and autochthonous (local) organic matters, with a focus on fish diets.
  • The study tested hypotheses suggesting that allochthonous contributions to fish diets are positively related to canopy cover, while essential fatty acids primarily come from autochthonous sources regardless of cover.
  • Results showed that autochthonous sources significantly contribute to fish carbon and essential fatty acids, even in streams with high canopy cover in northern Japan.
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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).

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The objective of this study is to investigate how the magnitude and occurrence of extreme precipitation events are affected by climate change and to predict the subsequent impacts on the wadi flow regime in the Al-Khod catchment area, Muscat, Oman. The tank model, a lumped-parameter rainfall-runoff model, was used to simulate the wadi flow. Precipitation extremes and their potential future changes were predicted using six-member ensembles of general circulation models (GCMs) from the Coupled Model Intercomparison Project Phase 5 (CMIP5).

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A central question linking ecology with evolutionary biology is how environmental heterogeneity can drive adaptive genetic divergence among populations. We examined adaptive divergence of four stream insects from six adjacent catchments in Japan by combining field measures of habitat and resource components with genome scans of non-neutral Amplified Fragment Length Polymorphism (AFLP) loci. Neutral genetic variation was used to measure gene flow and non-neutral genetic variation was used to test for adaptive divergence.

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To estimate the freshwater loss in coastal aquifers due to salinisation, a numerical model based on the sharp interface assumption has been introduced. The developed methodology will be useful in areas where limited hydrological data are available. This model will elaborate on the changes in fresh groundwater loss with respect to climate change, land use pattern and hydrologic soil condition.

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