Growth Situation of Phragmites australis (Cav.) Trin. Used in Artificial Floating Islands for Water Purification in Cold Regions

抄録

In this study, growth experiments of Phragmites australis (Cav.) Trin., used as part of artificial floating islands for water purification, were conducted. The Lake Mizusawa, which is the study area, is located in Biei Town, Hokkaido. The area around this lake is hilly and mostly comprises farm fields . Due to the topography and land use, soil particles and fertilizer flow into the lake after heavy rains. This is the most important cause of lake eutrophication. One way to clear up this eutrophied lake is to place artificial floating islands using the Phragmites on the lake surface. The Phragmites used for the artificial floating islands absorb nitrogen, including the contained in lake’s water, to promote lateral buds sprouting. After that, grown lateral buds are cut and hence the pollution is carried away outside the system. However, this method has been little tested in cold regions such as Hokkaido. Thus, on July 2010, we put artificial floating islands in the biotope which was developed on a drained paddy close to the lake. The Phragmites grew steadily. There were about four hundreds lateral buds sprouting by October 2010, and the maximum plant length of lateral buds was 0.74 meters. Observed artificial floating islands were left in the biotope during winter. In 2011, the lateral buds sprouted and grew in a shorter period of time compared to 2010. Similarly, maximum plant length of lateral buds was 1.86 meters. Ear emergence was also observed, although it was not observed in 2010. Therefore, it is considered that there was no damage to the Phragmites due to the cold. From these results, it was found that the Phragmites used for the artificial floating island were able to grow in cold region. Thus, this method is a promising way to improve water quality of Lake Mizusawa.