[A-HW24] Material transportation and cycling at the land-sea interface: from headwaters to the ocean

[AHW24-19] Evaluation of water and solute flux in a forest soil

*Masahiro Kobayashi¹, Yuko Itoh¹ (1.Forestry and Forest Products Research Institute)

Keywords:Soil water flux, Forest, Evapotranspiration

To clarify elemental dynamics in forests, it is necessary to evaluate the mass balance during the water flow through the canopy, soil layer, and discharge as stream water. However, long time observation of water flux in soil is not easy and requires considerable labor. Numerical methods using soil hydraulic conductivity and water retention data can be used to assess long-term soil water flux with minimum effort. In this case, it is important to incorporate water consumption by evapotranspiration in a proper way. In this study, we evaluated soil water flux in a Japanese cypress forest using a simple evapotranspiration model recently presented (Sawano et al., 2015) and a water transport program for unsaturated soils, HYDRUS1D. In this forest, soil water flux was observed using a porous plate lysimeter that controls suction according to the wetness of the soil. The throughfall was used as water input for the HYDRUS calculations, and only the evapotranspiration from the dry canopy (= transpiration) was calculated using the evapotranspiration model. The calculated water flux agreed well with those observed by lysimeter, suggesting that this method is applicable to the evaluation of long-term water and solute flux in forest soils. We also quantified the nitrogen leaching from the rooting zone using observed soil water nitrate concentration and the calculated water flux by this method.