寺内元基コラム「人工衛星観測データによる海の富栄養化監視」 GENKI TERAUCHI Column "Monitoring the eutrophication of the ocean through artificial satellite observation data"

The activities of humans in shore areas have a major effect on coastal ecosystems, and it is reported that over 40% of the world’s oceans have greatly been affected. Asian countries, one of the most densely populated areas in the world where there has been rapid urbanization of coastal regions, has seen considerable development of agricultural, fisheries, and manufacturing activities in recent years. There are concerns that the effects of such human activities will nega-tively impact oceanic environments. One of the negative effects is artificially-induced eutrophication. This occurs when there is an excessive nutrient, such as nitrogen and phos-phorus, caused by wastewater and factory wastewater draining into coastal ocean areas. As a result, organic matter is increased with the growth of phytoplankton, causing red tide and oxygen deficiency, leading to the extinc-tion of living things in the ocean.

Surfers, who are sensitive to changes in the ocean’s conditions, understand the dynamic changes of the coastal water in their skin. In Japan, since the enforcement of the Water Pollution Control Law in 1971, it has become an obligation of prefectures to regularly mon-itor the quality of the coastal public waters, such as rivers, lakes, marshes, harbors, and coastal areas. However, such monitoring is often conducted at a frequency of once per month, at some fixed points in time. There are limitations, temporally and spatially,
to observing the dynamically changing coastal environments. Thus, in the 1970s, NASA began launching artificial satellites to orbit and monitor the Earth from space, and experimented with observing the ocean environments with equipped sensors. With international cooperation, many space agen-cies, such as the Japan Aerospace Exploration Agency (JAXA), and other research institutes have developed and operated ratification satellites that enable observation of ocean en-vironments, and share the observed data on the internet for the common good.

At the graduate school of Nagasaki University, I majored in satellite biological oceanography. My research theme was to use remotely sensed chlorophyll-a concentration data, proxy for amount of phytoplankton, to monitor and assess marine eutrophication. Although adequate concentration levels of phytoplankton are necessary as a primary producer of the marine ecosystem, if there is too much it begins to cause the collapse of the ecosystem. The technique I developed ana-lyzes time series of ocean color data acquired from satellite observation in wide areas. First, the ocean is separated by high and low concentration levels in phytoplankton bio-mass. Then, the ocean is classified into three areas (increasing, decreasing and no trend) by detecting inter-annual trends. Then, by combining phytoplankton concentration level and the inter-annual trends, I classify ocean areas into six types (high concentration and increasing trend, high concentration and no trend, high concentration and decreasing trend, low concentration and increasing trend, low concentration and no trend, and low concentration and decreasing trend), and create a map of the ocean areas where eutrophication is likely to occur. As there are few precedents for techniques that combine concentration level and trends in environ-ment monitoring, it has been gathering recent attention globally as a technique to quanti-tatively evaluate the status of achieving the Sustainable Development Goals (SDGs) set by the United Nations. Going forward, with the increase in the volume of satellite data, we are starting to work with international technology companies, Google and JAXA, to utilize cloud computing technology and em-ploy the latest artificial satellite sensor data to monitor and assess marine eutrophication that could occur in coastal areas of the world’s oceans.

GENKI TERAUCHI
Born in Ishikawa Prefecture in 1976. PhD (science) holder, wooden surfboard builder, furniture designer. Representative at GT Designs/Chief Researcher at Northwest Pacific Region Environmental Cooperation Center. Prompted by starting to surf when he graduated university, he changed from working as a regular employee at a manufacturer to being an oceanographer. On the sidelines of his ocean research, as a result of pursuing surfing in the ultimate environment at one with nature, he began making surfboards with wood from the mountains upstream from the land. Leveraging the architecture knowledge he learned in uni versity, he established GT Designs in December 2017 by building a studio on the premises of his home and beginning full-blown manufacturing of wooden surfboards and furniture.