Dissolved matter concentrations of bulk precipitation, throughfall, stem flow, soil water, and stream water were investigated in two small forested watersheds consisting of sugi (Cryptomeria japonica) and hinoki (Chamaecyparis obtusa) trees, in Gunma Prefecture, 100km northwest of Tokyo. Processes of the changes in water chemistry were examined. Concentrations of nearly all kinds of dissolved matter in surface soil water apparently were affected by soil moisture, mineralization and nitrification, anion exchange capacity, throughfall chemistry and so on. Concentrations of Na+, HCO3-, and SiO2 and pH in subsurface soil water appeared to be affected by chemical weathering following an increase in CO2 from soil respiration. Soil respiration apparently also affected on concentrations of K+ and HCO3- in stream water. NO3- concentrations in stream water were affected by NO3- concentrations in subsurface soil water besides stream discharge. Concentrations of nearly all kinds of dissolved matter, except for NH4+ and H+, increases from bulk precipitation to stream water through the forest ecosystems. These increases in concentrations apparently were affected by the processes of evapotranspiration, leaching from trees, mineralization and nitrification, chemical weathering by soil respiration and so on.

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Several experiments on infiltration with soil column under constant rate rainfall were performed to verify the applicability of the Mein-Larson model. Comparing the observed data with those predicted by the model, we found excellent agreement between the measured and computed infiltration rates for initially air-dried soils. However, for the soils which have been wetted once, they showed somewhat variation in soil profile and no longer good agreement was obtained for infiltration rates. We proposed here three modified models of Mein-Larson model. In each model, the hydraulic conductivity (K), the capillary pressure at the wetting front (Hf) and the difference between the saturated water content and the initial water content (Δθ) was treated separately as a linear function of the soil depth. These models were used to fit the experimental data. The results indicated that the modified model which considered the K's variation appeared to be better applicable than the other two.

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Field observations on the snow surface heat budget are carried out under the different forest cover conditions. Using the heat budget model which was identified based on the observed data, the influence of forest on snow surface heat budget was examined. The results obtained are as follows; 1) Snow surface albedo and bulk coefficients at the open site adjacent to a forested area are almost same as the one in the forest. 2) Radiation and sensible heat budget decrease, as the percentage of solar radiation which is shielded by a canopy (Cf) increases. 3) Latent heat budget is independent of Cf.

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In order to estimate evapotranspiration from watershed by energy balance with accuracy, it is important to evaluate the total incident radiation by accumulating radiations on the hillslopes. As the necessity is recognized, researches considering slope solar radiation have been increased recently. Common model to estimate diffused solar radiation in these studies is not the anisotropic models, which have been widely applied in the field of solar energy, but the isotropic model which is based on simple geometric conversion. In this study, global solar radiation on tilted surfaces, global and diffused solar radiations on the horizontal surface were measured, and the two models were examined to estimate the global solar radiation on the slopes. The results show that the accuracy of the model depends on the method to measure diffused solar radiation. The anisotropic model is not accurate unless direct solar radiation is measured. The isotropic model is more accurate rather than anisotropic model and still useful with the present data level of solar radiation.

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