PARENT SESSION
Organized Oral Session 6: Development of landscape heterogeneity at multiple scales in wetlands
Organizer(s): B Warner and A van der Valk
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 516 A, Level 5, Palais des congrès de Montréal

Types of mires and their formation in Hokkaido, Japan.

Fujita, Hiroko^*,1, Inoue, Takashi², ¹ Botanic Garden, Sapporo, Japan² Laboratory of Land Improvement and Management, Sapporo, Japan

ABSTRACT- Because of Hokkaido's relatively cold climate and short history of development, 90% of the natural peatland remaining in Japan is in Hokkaido, the northernmost island of Japan. Of the peatland in Hokkaido, however, about 70% of the original wetland area has been lost due to human activities in the past 100 years or so. Wetlands of more then one hectare in Hokkaido number 150. Almost all (98.5% of Hokkaido's wetland area) are mires, and 107 of them are on lowlands (alluvial plains). These lowland mires can be classified into three categories by the location or circumstances of formation: i) located in the back swamp of alluvial rivers, ii) located in terrestrialized lagoons, and iii) formed under special conditions such as the combination of high precipitation, sea fog, and cold temperatures in summer. Many of these mires formed no earlier than about 3000 years ago, in conjunction with the sea level regression after the "Jomon transgression". However, some did form earlier, for example Habomai Mire (9000 - 10000 years ago) and Ochiishi-misaki Mire (4600 years ago), both of which are in the coastal terrace of the Nemuro Peninsula. The mires on the western, Sea of Japan side of Hokkaido, which has heavy snowfall, also were formed earlier. These include Sarobetsu Mire (6000 - 5000 years ago), and Utasai Mire (5500 years ago). Although mires in mountainous areas were formed at widely varying points in geological history, most are believed to have formed in the postglacial age, when the climate was relatively warm and the precipitation high. Most lowland mires are fens that are recharged by mineral-rich water. However, Sarobetsu Mire, Ishikari Mire, Bekanbeushi Mire, and Shibetsu Mire have partially developed bogs that are recharged by rainwater. Stratigraphic studies of peat have shown that, in many cases, fens are influenced by repeated flooding at the early stage of formation, and then gradually replaced by ombrotrophic bog. The peat domes of bogs in Hokkaido are lower than that of raised bogs in Europe. Peat in Japan often includes several layers of volcanic ash, but this rarely hinders peat formation. However, in the downstream areas of Kushiro Mire, the volcanic ash that was carried and deposited there by surface runoff has influenced the peat accumulation.

Key words: lowland mire, back swamp, volcanic ash, peat formation