河川の整備および管理の違いがミクリ属等の水生植物の生育に及ぼす影響―巴波川（栃木県栃木市）の事例―

抄録

In this study, the differences in maintenance and management of an urban section of the Uzuma River (Tochigi City, Tochigi Prefecture, Japan) was investigated for influences that cause the growth of hydrophytes such as Sparganium L., which is described in the red data books of the Ministry of the Environment (2000) and Tochigi prefecture (2005). The investigated sections consisted of the three types of the two-plane concrete protection, the hydrophilicity shore protection and the natural type river. In the two-plane concrete protection, the hydrophytes of Potamogeton subfuscus and Sparganium japonicum were growing in places where the water springs flowed, however, Sparganium japonicum, which was located downstream of a diversion weir for agriculture, showed local distribution. We considered that a rapid flow was caused, sand was removed, and establishment of Sparganium japonicum was difficult when the diversion weir for agriculture was opened by the rising of the river. In the hydrophilicity shore protection, only Sparganium erectum was found. We considered that this was because the flow of the river became slower due to a widening of the river channel, the fine sand and silt soil piled up, and the growth of Sparganium erectum was promoted. In the natural type river, the range of growth of Sparganium japonicum was reduced in places where the riverbed was dug. We considered that this was because the rhizome of Sparganium japonicum was removed by the digging up of the riverbed. Therefore, as for the growth factors of hydrophytes, we consider stream management with a diversion weir for agriculture and an artificial riverbed excavation and river channel widening to have had a great influence.