Hydrological setting of infertile species-rich wetland--a case study in the warm temperate Japan

The detailed groundwater flow and water chemistry to illustrate landscape structure of the infertile peatless mire by using piezometers and groundwater wells were measured. The instruments were installed in lines through a small spring-fed wetland underlying little peat from the hillslope to the valley bottom in southwestern Japan. Flow net and EC data clearly indicated that the wetland was situated in a high-EC groundwater upspring area. The low-productivity graminous vegetation was related with four hydrological factors such as: (1) high water level; (2) low-EC (< 25 micro S/cm) groundwater; (3) weakly upward hydraulic gradient; and (4) overflowing of negatively pressured groundwater. In other words, the "old or deep groundwater" constructed the foundation of slope-wetland, and maintained the high groundwater level. In contrast, overflowing "youthful groundwater" is supplied from head of slope-wetland preferentially through the shallow substratum. The plant communities of the peatless mire in southwestern Japan are similar to those of raised bog in northern cool temperate Japan. There have been some reports verifying that the underlying mineral substrata of such wetlands were quartzile rocks such as granite, rhyolite, chart and well-leached sand. Results showed (1) low cation availability affect the water acidity; (2) upward seepage of high-EC groundwater composed the foundation of the investigated peatless mire; and (3) the poor mineral condition seems to play a similar role to northern ombrotrophic (rain-fed) condition.