Estuarine and Coastal Environment, Coastal Engineering and Management, Sustainability Science


Perspective of Research

Sasaki’s Laboratory aims to contribute to creation of safe, prosperous and attractive coastal environments, mainly in estuarine, coastal and inland waters. We consider both aspects of basic scientific and technological research and transdisciplinary research aiming at resolving concrete environmental and societal problems. To make contribution to research outcomes in the science and engineering field, it is the royal road to focus on the selection of a specific and significant theme, aiming at the most advanced and original works. In such a scientific and technological approach, we perform studies on, for instance, reproducing and predicting physical and biogeochemical processes in estuarine and coastal waters, aiming at enhancing technology for hind-casting and forecasting of the environment change. Studies that deepen each individual process are in general standard in traditional discipline-based research. However, considering the mission of our graduate school of promoting transdisciplinary studies and the characteristics of “environment” where holistic viewpoints are essential, we also try to integrate basic scientific and technological outcomes. We have been working on numerical prediction (computer simulation) based on process based modeling and field measurements. In addition, with the recent availability of rich environmental monitoring data and statistical modeling frameworks, we are beginning to take a data science approach as well. Such studies are mainly covered in Department of Socio-Cultural Environment Studies.
Meanwhile, with the growing significance of studies contributing to solution of pragmatic environmental problems, transdisciplinary studies have been getting more important. Sustainability Science may be considered as one of the first contributing fields in this aspect. In order to contribute to resolving concrete problems related to the environment and society, a specific problem in a specific area should be targeted. We perform field surveys (e.g., questionnaire survey, interview survey, focus group discussion), analyses of geographic information system (GIS) data, as well as integrating the results in various disciplines, such as aerial photogrammetric using satellite images (remote sensing), application of locally specialized simulation. Many of individual academic disciplines (especially, science and technology fields) have been matured, and it has been becoming possible to apply those outcomes for resolving local issues effectively and it becomes possible to create new knowledge by an integrated approach. This transdisciplinary approach is covered by both in Department of Socio-Cultural Environmental Studies and Graduate Program in Sustainability Science, Global Leadership Initiative( GPSS-GLI ).

Relation with Disciplines

Sasaki’s Laboratory belongs to the Graduate School of Frontier Sciences aiming at the integration of disciplinary outcomes. Dr. Sasaki is originally from the field of coastal engineering and environmental hydraulics in civil engineering. He has been one of the initial members at Division of Environmental Studies, Graduate School of Frontier Sciences, established in 1999 (except from 2002 to 2012 working at Yokohama National University), and since that time he has been working on transdisciplinary studies integrating outcomes in the fields of engineering, fisheries science, agriculture, statistics, environmental science, policy and management, and international development studies.

Research Topics

Research topics are introduced below. You could see summary of some studies through the links above the right side column. Other studies may be possible and if there are any requests, please contact Dr. Jun Sasaki.

Social Implementation of Blue Carbon

Do you know blue carbon? Blue carbon is a relatively new term, the United Nations Environment Program (UNEP) named “carbon sequestered and stored by the action of marine life” as blue carbon in 2009. Phytoplankton, seagrass (eelgrass), seaweed (kelp, sargassum, brown seaweed, laver), mangrove, and tidal marsh are thought to absorb carbon dioxide (CO2) by photosynthesis and suppress the increase in atmospheric CO2 concentration. Although this fact itself has been known for a long time, in recent years it has attracted attention as one of the new options in countermeasures for CO2 sinking source. Measures for absorption of CO2 by blue carbon are restoration and creation of seagrass and seaweed beds, tidal flats, tidal marshes and mangrove forests. Through their enhancement of coastal ecosystems, they also contribute to ecosystem services (supply of food through fishery resources, purification of water quality, tourism and recreation, prevention and mitigation of coastal disasters) and enhancement of the value of coastal environment. In addition, due to ecosystem-based measures, there are features such as high sustainability and low ethical barrier in social implementation.
NDC (Nationally Determined Contribution) was announced in the Paris Agreement in 2015, and Australia, India, Bahrain and the United Arab Emirates declare utilization of blue carbon as a measure to mitigate and adapt to climate change. Although Japan does not declare the use of blue carbon, we will clarify the features of blue carbon and estimate its potential, and will continue research on strategies for its social implementation.
From the viewpoint of blue carbon, it is important to estimate how much amount of carbon dioxide sequestered and stored as blue carbon along with its time scale for returning to the atmosphere. Marine phytoplankton actively absorbs carbon dioxide by photosynthesis, but at the same time, a large portion of them are decomposed to carbon dioxide in a short time, returning to the atmosphere. On the other hand, part of the organic carbon in seagrass beds (not only seagrass itself but also the organic carbon taken in the ecosystem of the seagrass beds) accumulates in their sediments for a long time, which is considered as its high retention function as blue carbon. It is necessary to quantitatively evaluate the possible carbon storage expected by creating these seagrass beds. Further, some of their leaves are transported to offshore and reach the deep ocean. Consequently, the return of the carbon to the atmosphere can be extensively delayed for hundreds of years or more. It is necessary to clarify what kinds of carbon sequestration and storage functions are performed on various time scales and how much they are effective. For this purpose, we are planning to conduct research utilizing field data on many existing marine ecosystems.
From the viewpoint of social implementation, it is necessary to know the expected time, area and amount of ​sediment resources (dredged sediment in ports and navigation channels and steelmaking slag) that can be utilized to create seagrass and seaweed beds. Using these data, we will consider strategies for creation and restoration of seagrass and seaweed beds. Also, it is important to clarify how much blue carbon potential in the coastal area of Japan or any country can be expected in case when there is no constraint on the amount of available sediment. Furthermore, from the perspective of how to secure financial resources and human resources, we can expect a framework of public-private partnership, such as the Public-Private Forum for Tokyo Bay Restoration, established in 2013, to implement in the society.

Numerical Prediction of Long-Term Environmental Change in Estuarine and Enclosed Coastal Waters

In recent years, the overall water quality in Tokyo Bay, one of the most polluted bays in the world, has been improved (actually the pollutant load, including total nitrogen (TN) and total phosphorus (TP), has significantly decreased), but hypoxia and anoxia often occur at the bottom water during summer. In addition, upwelling of the bottom hypoxic and anoxic waters and their intrusion into the surrounding tidal flats and shallow water areas sometimes lead to mortality of benthic animals, such as short necked clams (one of the major fishery resources). Since there has been almost no trend in decrease in the amount of the bottom hypoxic waters for a long time, it is important to propose effective and practical measures for it. In addition, the fish catch in Tokyo Bay, formerly called Edo-Mae (fresh fish caught in the sea near Edo, the former name of Tokyo), has decreased to less than one tenth compared to the those in 1960s. Although the total pollutant load control system (TPLCS) has been implemented since 1979, leading to overall improvement of water quality, hypoxia and anoxia have not been mitigated and fish catch has declined continuously. Some researchers in fishery science claim that the decline in fish catch may be partially caused by nutritional deficiency due to the TPLCS. Thus it would be the time to reconsider the management and control of water quality in the bay to achieve a balanced and flourishing coastal marine environment. Furthermore, it is speculated that climate change impacts may also be associated with long-term water quality fluctuations. Using monthly field monitoring data in public waters collected by local governments for more than 40 years, statistical modeling and analyses are required for identifying seasonal components, eventual factors (disturbance caused by typhoons, effects of river floods, etc.) and trends.
Based on these backgrounds, monitoring of water quality as well as sediment quality, and full-scratch numerical modeling and prediction of long-term hydrodynamic and biogeochemical processes have been performed through integration of circulation, wave-hindcasting, pelagic ecosystems and multilayered sediment processes. We will also work on research on proposals of effective measures for environmental restoration, rehabilitation and mitigation along with their effectiveness and feasibility. In addition, we actively apply open source numerical models, such as FVCOM, for seeking better management in estuarine and coastal waters.

Environmental Restoration, Rehabilitation and Mitigation in Estuarine and Coastal Environments

Factors associated with degradation of water quality and ecosystems in coastal environments include not only pollutant loads but also environmental infrastructure, such as topography and sediment grain size. For example, short-necked clams inhabit sandy tidal flats and shallow water beds, feeding phytoplankton by filtering seawater. Some of the organic matter taken up constitutes their body, some is used for respiration and decomposed, and some deposited on the sediment. As a result, the existence of the habitat of clams has a function of suppressing the deposition of organic matter originating from phytoplankton on the offshore deep beds where hypoxic and anoxic waters tend to appear typically in Tokyo Bay. Owing to the long-term reclamation of the foreshore in Tokyo Bay, tidal flats and shallow water areas have been decreased, leading to decline in water purification function, including its decomposition and storage, in coastal waters. Restoration, rehabilitation and mitigation of tidal flats and shallow water areas are expected to restore the sound material cycling and lead to restoration of coastal marine environment.
For the purpose of examining such environmental restoration measures and predicting their effect, we have been performing field observation and numerical modeling and simulation. In addition, through the activities in the Public-Private Forum for Tokyo Bay Restoration and a project team of Restoration and Creation of Habitat under the forum, we will consider developing new ideas for environmental restoration measures on the basis of scientific evidence and their effective and feasible implementation in the society. It has been necessary to renovate aging coastal structures, such as seawalls, and further consideration for balanced and environmentally friendly structures is becoming important.

Local Water Quality Improvement Using Technical Countermeasures

Dredged pits made by mining of sediment resources are sometimes distributed in coastal waters. In Tokyo Bay, such dredged pits exist off Urayasu, off Akanehama, off Makuhari and off Kemigawa. Waters in dredged pits are often stagnant and as a result their water quality is sometimes extremely degraded, leading to generation of anoxia.
At the Tokyo Olympics and Paralympic Games in 2020, Odaiba Seashore Park is planned to be the venue for triathlons and swimming competitions (10 km marathon swimming). As the Tokyo Metropolitan area has a combined sewer system where rainwater and sewage are collected in the same sewer pipes, the flow rate increases drastically during heavy rain, resulting in exceeding the capacity of processing and discharging the untreated water to the environment. Thus it is concerned that the number of coliform bacteria may exceed the standards of the competition.
Regarding such local water quality problems, we have been performing field and numerical investigation on effective countermeasures using various technical devices and methods of controlling discharges of adjacent rivers.

Statistical Identification and Stakeholders’ Perception of climate change in Coastal Waters

Phenomena that are considered to be the effects of climate change, such as an increase in air and water temperatures and a change in typhoon trucks, have been observed in the world. Engineers in construction companies involved in marine civil engineering have perceived and concerned a decrease in the duration of a calm wave condition under which the installation work of a caisson (a huge concrete box used for breakwater) can be performed. In fact, in some coastal areas, a statistical analysis has revealed that the frequency of high waves and long waves (Long waves increase the horizontal movement of the water mass even when the wave height is not so large, which makes construction difficult.) has been increasing. Based on statistical analysis of observation data and interview survey of stakeholders’ perception and opinion, we are trying to identify long-term trends of the influence of climate change to consider adaptation measures, including amendment of regulation for marine construction works.

Coastal Zone Management for Sustainable Coast in Developing Countries under Climate Change

In coastal areas of Southeast Asia and South Asia, the impact of climate change is considered to be becoming more apparent than in Japan. This impact may be getting worse as it is strengthened by land subsidence and mangrove deforestation. we have been conducting research aiming at contributing to the sustainable development and utilization of coastal areas in developing countries under the influence of climate change.
Our current targets (and collaborators) are disaster mitigation using mangrove forest in Mekong Delta in Vietnam (Can Tho University), sea level rise and sediment transport in Pondok Bali and the Cipunagara River mouth areas in Indonesia (Bandung Institute of Technology), mangrove restoration at the head of the Upper Gulf of Thailand in Thailand (Burapha University), coastal erosion in Marawila Beach in Srilanka (Coast Conservation Department, Srilanka), salinity intrusion and resultant health crisis and environmental migration in the southwestern area of Bangladesh, environmental protection and sustainable use of coral reef in El Nido, the Philippines, tsunami disaster mitigation in Oman Sea, Iran, and environmental management in Bohai Sea in China. In the near future, we will start studies on evaluation of ecosystem service in a river in Jessore, Bangladesh and on restoration of mangrove in Myanmar.
In these studies, we are conducting survey on stakeholders’ perceptions and field measurements for proposing possible countermeasures, as well as evaluating projects of mangrove restoration, analyzing influences of salt intrusion and inundation caused by sea level rise (including ground subsidence).

Mitigation of Coastal Disasters, including Storm Surges and Tsunamis

We have also been involved in studies on mitigation of coastal disasters, including storm surges and tsunamis. Since participating in a reconnaissance field survey for the 2004 Indian Ocean Tsunami held in southern coasts of Srilanka and Banda Aceh, Indonesia, we have conducted several tsunami and storm surge disaster investigations, including the 2011 East Japan great earthquake and tsunami. We have been developing a numerical system using the unstructured-grid, finite volume community ocean model (FVCOM) developed by Chen et al. (2003) that can precisely reproduce complex coastlines and structures. In the Great East Japan Earthquake and tsunami, we conducted collaborative research with the development group of FVCOM in the study on the tsunami impacts and spread of radioactive contaminated water due to the accident of the Fukushima Daiichi Nuclear Power Plant.