**4.4 Proposed mechanisms of pore water movement**

Figure 7 illustrates the conceptual image of the pore water movement in the tidal mud due to the seasonal variation of temperature. During spring and summer, the temperature at the shallow depth of the Iida tidal mud of the Ariake sea was higher than that of deeper depth, whereas opposite phenomenon was found during autumn and winter. The temperature gradient in the mud causes pore water to move in the vapor phase from a higher temperature site to a lower temperature site. The vapor condenses at the lower temperature area and becomes water, which increases the total head and drives the water liquid phase from lower temperature site to the higher temperature site (Nassar et al. 2000). Aforementioned process is titled coupled heat-pore water vapor-pore water liquid flow, as shown in Fig. 7.

Fig. 7. Proposed concept of coupled heat-pore water vapor-pore water liquid flow in tidal flat
