2A.Research on Improving Water and Sediment Quarity in Enclosed Bay

Background and Objectives

  • Tokyo Bay, Osaka Bay, Ise Bay, and other enclosed bays are recovering from the past degradation of water quality, and people's expectations and concerns are shifting from merely achieving "a clear sea" to restoring "a sea rich in biodiversity," as evidenced by the recovery targets stipulated by the respective Bay Renaissance projects. Meanwhile, the Ministry of the Environment plans to add oxygen concentration of the bottom layer, transparency, and other parameters closely related to habitat to its new water quality standards. Thus, new technologies are needed to ensure a diverse habitat, including the reduction of hypoxia that continues to threaten habitats.
  • However, a report published by the United Nations Environment Programme (UNEP) in 2009 places great emphasis on conserving coastal ecosystems such as seaweed/ seagrass beds that actively absorb and sequester carbon dioxide, thus mitigating global warming. This concept has quickly drawn attention along with the term "Blue Carbon."
  • Given this background, the theme includes research and development on restoring coastal sea areas to help create a richly diverse habitat while contributing to the mitigation of global warming. In order to achieve these goals, we are conducting research to propose measures against flows that hinder the habitat as well as to improve water and sediment quality. We are also working on consolidating fundamental ecological and geotechnical knowledge regarding tidal flats and seaweed/seagrass beds so as to conserve, restore, and create these habitats by effectively
    using dredged materials.

Research topics

  • This theme focuses on basic research on the processes of exchange with the open sea, the mechanisms of fine-particle transport and mass circulation in the benthic boundary layer, and the basic structure and function of seagrass bed and tidal flat ecosystems, which are particularly important in terms of the physics, chemistry, and biology of coastal areas.
  •  Regarding the ecosystems of tidal flats and shallow waters, we aim to restore the biodiversity of coastal seas in Japan based on the results of research on the feeding ecology of higher trophic-level organisms and the association between geotechnical criteria and benthic life.
  • Additionally, we are examining the degradation of sediment quality and the function of borrow pits as the causes of hypoxia and blue tides, and are organizing the technologies for improving the water environment, including pit filling and sediment capping. We are also exploring evaluation tools in order to select and combine the most suitable available methods for restoring the environment of inner bays.
  • Regarding dredged materials, which are considered the best material for environmental reclamation, our R&D is focused on promoting the effective use of dredged sediment for the creation of habitats while ensuring chemical safety.
  •  Furthermore, we are examining carbon flows in coastal areas to quantify and enhance the carbon dioxide absorption and sequestration capacity of coastal ecosystems.

Activities in FY 2014

  • We observed the actual underwater air quality at seaweed beds, tidal flats, their basins, and the open sea throughout Japan. We carried out experiments on carbon dynamics using a tidal flat tank and a Mesocosm tank while examining the measuring methods. We also developed on-site observation and analysis systems of carbon dynamics as well as ecosystem models focusing on carbon. If this study clarifies the CO2 absorption effect of coastal ecosystems, it will be developed into a proposal for making good use of the effect (including the increased CO2 absorption by the development of Zostera beds and economic effects of greenhouse gas emission right trading).


Photograph Scenes of observation of CO2 flux

  • We conducted rearing experiments concerning the prey selection of birds and the influence on the whole food web. We found that there are fewer minute small animals due to predation and more plants (including biofilm) due to nourishing droppings in the experimental areas with birds compared to those without birds.
  • We collected data on the shapes and behavior of birds by collecting, temporarily capturing, and photographing prey organisms and droppings in tidal flats and wetlands while analyzing their feeding habits using image analysis data of their form and feeding behavior as well as stable isotope ratio and calorimetric analysis data. We also studied the form and behavior that determine the structure and dynamics of food webs. Applying the results of these studies, we proposed a method of designing tidal flats that provide suitable habitats for birds. This proposal is expected to be utilized in the development of higher quality tidal flats in the future. Meanwhile, in assessing the environmental impact of the expansion work of Delta Port in Vancouver, Canada, the Environment Canada Ministry officially designated the preservation of microorganisms proven to be the staple food of birds in this study as an important evaluation item, and their assessment is now in progress.

Figure Food web in a tidal flat
(Those written in red are changes due to rearing birds in a laboratory.)


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