Global warming is one of today's major threats to the environment. It is caused by an accumulation of carbon dioxide resulting from the burning of fossil fuels. Plants are believed to absorb and store part of these carbon particles but when it rains, the water washes them into the soil and rivers and out into the ocean. During a typhoon, this phenomenon increases considerably.
The transfer of organic carbon from land to sea via erosion and through rivers is an important part of the global carbon cycle. According to the study, "More than one third of this organic carbon flux comes from sediment-laden rivers that drain the mountains in the western Pacific region, large parts of which are covered in forests."
Researchers in Taiwan took sediment samples from the Liwu River, on the east coast, before and during Typhoon Mindulle hit the island in July 2004. The samples were then sent for analysis to Robert Hilton, a doctorate student in the Department of Earth Sciences at the British University of Cambridge.
According to the study, every year 50 to 90 million tons of organic carbon may enter the ocean from islands of the west Pacific, and about 5,000 tons were washed down the Liwu River during typhoon Mindulle alone.
The torrential rain and floods triggered by the typhoon drained the mountains of soil and vegetation and flushed everything down the Liwu River and out to the sea. The floodwater, heavy with mud and silt, sank to the ocean floor, effectively locking away the carbon stored in the sediment. For this reason, the researchers believe typhoons provide ideal conditions to bury carbon into the seabed.
"We were often told of the global carbon cycle, but thanks to the typhoon's torrential rains we were able to collect enough data to evidence it," said study co-author Chen Hongey, a professor of earth sciences at National Taiwan University.
The research seems to echo "carbon sequestration," a new technology that is currently used in Norway and the United States to bury carbon dioxide produced by industries deep underground or in the ocean. Researchers, however, are not able yet to calculate the exact cost or benefits of such a technology.
As the study proved, a storm washes out a lot of soil and plants containing greenhouse gases into the sea. This might help reduce slightly the level of carbon dioxide thus slow down global warming, but Chen reminded that meteorologists are predicting typhoons may become more powerful in the future because of global warming. "The point is: Nature is doing its part in bringing down the level of manmade carbon dioxide. Shouldn't we do something too?" he asked rhetorically.
Chen explained their research showed that before the typhoon hit the island, the proportion of carbon from plants and soil in the Liwu River measured 10 percent and 90 percent, respectively. After the typhoon, however, the amount of carbon from soil dropped to 57 percent, while carbon particles from plants rose to 43 percent.
Trees and vegetation in the midstream and upstream part of the Liwu River washed down by the heavy rain had raised the proportion of plant carbon in the runoff from the river, he elaborated.
"We all heard trees absorb carbon dioxide, and we confirmed this theory by using precision instruments to analyze small amounts of carbon particles," Chen continued. Therefore, as a solution for mountainous islands such as Taiwan, he suggested planting more trees in the middle and upper parts of rivers and avoiding the exploitation of those areas.
The more trees, the more carbon dioxide will be absorbed, he explained. This in turn might help moderate the frequency and intensity of typhoons that wreck havoc in people's lives every year.
Write to June Tsai at june@mail.gio.gov.tw