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NatureInterface > No.02 > P030-033 [Japanese]

Towards a Beautiful, Safe, and Lively Seashore -- Masahiko Isobe








Towards a Beautiful, Safe, and Lively Seashore

MASAHIKO ISOBE

The University of Tokyo

Graduate School of Frontier Science

Department of Environmental Studies

The seashore is the connecting point, and boundary, of the sea, the land, and the air. It is also a point where freshwater changes to saltwater. Waves, flows, and winds are generated at seashores. Thus they have special features, different from the land or sea.

Japan is an island country surrounded by long shorelines. The total length of the shorelines is about 35,000 km (ca. 22,000 miles). One-third of them are natural seashores, and the rest are artificial. The total length of the shorelines of sand, cobble beaches, and muddy beaches are less than 10,000 km (ca. 6,000 miles).

Only 32% of the cities, towns, and villages in Japan are on seashores. But 60 million people live at seashores, industrial sales at seashores is 47% of the gross national sales of industry, and commercial sales at seashores generate 77 % of the amount of money earned by all commercial industries in Japan. Seashores are therefore important places. They support large populations, and many economic activities.

The Nature Interface interviewed Prof. Masahiko Isobe, head of the Department of Environmental Studies at the Graduate School of Frontier Science at the University of Tokyo, about the importance of seashore environments.

Three Components of Seashore Environments

Seashores have three components related to the natural and social environment: 'Nature and ecology,' 'Safety and disaster prevention,' and 'development and utilization.' Professor Isobe talked with Nature Interface about the roles of these three components.

*Nature and Ecology

Seashores and the shallow parts of the sea around them are good environments for marine organisms, since oxygen dissolves through the ebb and flow of the tide and the movement of the waves. These areas also receive a lot of sunlight. The surface area of seashores is slight compared to the entire area of the globe, but they are important for life; more than one-half of marine organisms live or breed there. Seashores are abundant with plants and animals such as fish, microbes, benthos, plankton, birds, seaweed, shore plants and forests.

Shore areas have reef areas, sandy and muddy areas, tidal flats, macrophytic beds, etc. Macrophytic beds are created on reefs, and are important places where fry grow. Tidal flats are important wetlands in Japan, which is surrounded by the sea. Tidal flats play important roles in biological production through their regulation of the weather and purification of the air and water, and are key areas for environmental conservation. Tidal flats are also good recreational places for such activities as shell gathering, fishing, and bird watching.

Macrophytic beds are described as sea forests, with various species of seaweed and sea grasses. They are also where fish live and spawn. Nitrogen and phosphate are absorbed, and oxygen is photosynthesically supplied by seaweeds and sea grasses.

*Safety and Disaster Prevention

Measures for safety and disaster prevention at coastal areas are important, given the high population density in these areas, and the significant role they play in business and industry. Besides the problems of coastal erosion and land subsidence, coastal areas always face dangers from high waves, flood tides, storms, floods, and tsunamis caused by earthquakes.

The Sea Coast Law was enacted in 1956 for the prevention of such disasters, and coastal areas were viewed as areas to protect. There were various natural disasters before World War II. After World War II, there were several severe natural disasters, such as the Isewan Bay Typhoon in 1953, and the tsunami caused by the Chilean Earthquake in 1960. Such disasters made people work harder on disaster prevention at coastal areas, and accelerated the development of harbors and constructions for shore protection and for building banks. In consequence, shorelines in Japan were gradually changed from natural shorelines to artificial ones.

However, people gradually started to change their consciousness of nature and development and to ask for protection for natural seashores. In this way, The Sea Coast Law was amended in 1999. The law was reviewed further since then, in order to attain the objectives of coastal protection, environmental conservation, and utilization.

There is another significant problem: erosion of shoreline sands. Japanese seashore sand is eroded by some 0.17 meter (ca. 7 inches) each year, because the amount of sand supplied by upper streams is decreasing, due to the construction of dams. At seashores, sand absorbs wave energy, and the decrease in sand significantly decreases a shoreline's protection from high tides.

*Development and Utilization

Coastal areas can be developed and utilized for transportation, obtaining energy, fisheries, agriculture, industry, business, marine recreation, and other uses. People utilized the sea for marine transportation for business from olden times, and harbors were developed for ship anchorage and shipping and for discharging products, besides being utilized for fisheries. Business and industry expanded in coastal areas, which were convenient for shipping products, and effective for business. Many power plants are built near coastal areas, because coolants are easily obtained.

Now, the utilization of marine temperature difference energy, wave energy and tidal energy are being examined.

Toward Coastal Environment Management

Ideal coasts are those that have natural sand on their shores, guard against disasters, and can be utilized for business, industry, and recreation. These functions seem to have no relationship with each other, but are important for recognizing and promoting the three roles of coasts: ecology, disaster prevention, and utilization.

Coasts can be topographically changed by many factors. Thus, the natural sands must always be maintained at a stable amount. When we regard coasts from the viewpoint of ecology, there are ecosystems typical in the sands. The sands offer places to grow to benthos such as bivalves. The eggs of sea turtles are laid and hatched there. When we regard coasts from the viewpoint of disaster prevention, the maintenance of the sands mitigates the effect of high waves or high tides, because the sands absorb the wave energy. As a consequence, buildings and houses near the coasts are protected, and marine recreation can develop and become popular in such areas.

To protect the organisms in coastal areas, people have tried creating macrophytic beds on artificial foundations, in areas where natural foundations were damaged or destroyed, and by maintaining the biomass of bacterium to that in tidal flats. Topography is a basic environmental component in the coastal environment, and needs to be conserved through the management of sediments at coastal areas. Now, we'll look at coastal erosion, an important factor in the topographical changes of Japanese coasts.

Coastal Erosion in Japan

Disaster prevention of high waves and tides used to be the main concern in coastal conservation. However, from around 1980, embankment for coast protection, the creation of artificial reefs, and beach nourishment became more important concerns. This shows how serious the coastal erosion problem is. J apan loses 160 ha (ca. 400 acres) of land every year by erosion. If the situation doesn't change, Japan will lose 2400 ha (ca. 6000 acres) after 10 years, and 4800 ha (ca. 12,000 acres) after 25 years, which is equivalent to the sizes of Niijima Island and Miyakejima Island, respectively (Fig. 1). (Note: Niijima Island and Miyakejima Island are well-known Japanese islands and are a part of the Tokyo metropolitan area.)

Construction of dams at rivers, exploitation of sediments, and the inhibition of sediment supply by the sea through the protection of sea cliffs are some reasons for accelerating coastal erosion. Thus, the amount of sediments supplied should be increased to prevent further erosion. We need to manage sediments comprehensively at rivers and coasts using the beach nourishment technology. The topographical features of Japan, which consist of mountains and islands, need to be brought into balance between their natural cycles and the artificial measures needed to manage them. It is necessary for us to consider the harmony between the three components we have been speaking of, ecology, disaster prevention and utilization.

Sea-level Rise by Global Warming

We must consider the effects of the sea-level rise, caused by global warming, on the coastal environment. Decrease of the sands and submergence of the land below sea level may cause environmental disasters. We need to take measures to prevent such disasters on a global scale.

For proper environmental management, we need to promote the monitoring of coastal areas to deal with environmental issues that occur there. Sensors utilizing the change of water pressure, the Doppler effect of ultrasonic waves and electromagnetic induction, are used as wave height sensors and flow meters to monitor the waves and flows, which are external forces that coastal areas receive. To monitor the water quality, water temperature proves, salt concentration meters, dissolved oxygen meters, chlorophyll a concentration meters, etc. are used. (Note: A concentration of chlorophyll indicates a biomass of plant plankton.) We look forward to the development of sensors to anticipate red water. We also hope that wearable computers, that allow people or dummy submarines to obtain real-time data on coastal area environments, will be developed though technologies different from those used to monitor the environment on land.

In this issue of our magazine, we introduced basic information on coastal area environments and their management. In the next issue, we will investigate each ecological problem introduced here in more detail, and will also introduce works published abroad on each of these problems.

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