Sap flow velocity was measured by the heat-pulse method in a forested catchment (1.16 km2 in area), and transpiration from the catchment was estimated by three-dimensionally simulating actual sap flow blocked by sensors of definite size. The catchment is mostly forested by 56 % Abies sachalinensis (Sakhalin fir) and 44 % mixture with broad-leaved trees. Radial distributions of sap flow in the sapwood part for representative fir and broad-leaved trees were obtained by the heat-pulse method, and then transpiration Tr1 (L day-1) of each tree was calculated by integrating the sapwood area. The Tr1 values averaged for non-rainfall days proved to be highly correlated to trees’ breast high diameters DBH (cm) with R2=0.93 for Sakhalin fir and R2= 0.71 for broadleaved trees. The catchment transpiration averaged over non-rainfall days was 0.72 mm day-1 for the heat-pulse method and the catchment evapotranspiration, 2.03 mm day-1 for the Penman-Monteith method. The possible underestimate of transpiration from the heat-pulse method is probably due to the ignorance of sensors’ size originally supposed in the heat-pulse method. Actual sap flow blocked by sensors of 2.8 mm in diameter was three-dimensionally simulated. Giving the cut size of 2.8 mm by the sensors in the simulation, the catchment transpiration was estimated at 1.76 mm day-1. This value is likely reasonable to the evapotranspiration at 2.03 mm day-1 from the Penman-Monteith method, since the evapotranspiration includes the evapotranspiration from forest floor covered by striped bamboo (Sasa senanensis).

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The authorhasobservedand measuredthephysicalproperties ofHitiomi-numa Pond,a smallpond inthe Sarobetsu Mirefor about ten years.There isafloating isletin thepond. Fromthe survey, it was found outthat the floating isletvirtuallysinkseverywinter. In order to understand this sinking mechanism, the authorfixed an absolute-pressurewater levelgauge into the floating islet.Thereby, sinking depths of the islet were continuously measured, while water temperature was monitored at some certain water depths.Meanwhile, the author modifieda prototype model for simulating thermal conditions of a pond.Definingthe differences betweensummer and winter boundary conditions, a new model was built up for quantitatively explaining the mechanisms of water temperature distributionsandthefreezingprocessesof the pond.Numerical simulations by the model allowed us to understand the thermal variations ofthepond, since the model well simulated the freezing process of the pondsurface. Furthermore, it was revealed that there is a close relationship between the freezing process andthe sinking mechanism of the floating islet in winter.

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