Quantitative evaluation of stemflow flux during the rainfall-discharge process in a forested area

Stemflow is very important as a point spot input of precipitation and tree solutes to the ground surface in a forest. However, it has not been attached importance for its hydrological significance because of its quantitative contribution per unit area when compared to throughfall. In the densely forested area with relatively high rainfall, some studies recently point out that stemflow has a significant influence on runoff generation, soil erosion, groundwater recharge, soil solution chemistry, and the distribution of understory vegetation and epiphytes (Levia and Frost, 2003). It is known that there exist clear differences of isotopic composition and chemistries in the gross rainfall, throughfall, and stemflow, even in a rainfall event. In order to evaluate the stemflow contribution for the infiltration into a forest soil and groundwater, the precise isotopic observation for rainfall and river discharge water during rainfall-discharge process has been conducted in a densely forested headwater catchment of Kahoku experimental forest (KHEW: 33o08'N, 133o43'E) , Kyusyu island, Japan, since June, 2004. Water samples of gross rainfall, throughfall, stemflow, and riverwater were collected every hour using automatic water sampler. These samples were analyzed for deuterium and oxygen stable isotopes, inorganic water chemistry, and dissolved Silica. To evaluate the stemflow contribution during the rainfall-discharge process, catchments scale tank model was considered by using stemflow and throughfall as an input, and an isotopic fluctuation of river water during rainfall event was calculated by this model which was evaluated by the observed isotopic fluctuation in the river water. In the AGU fall meeting, we will explain more precisely about the quantitative evaluation method of stemflow contribution during rainfall-discharge process by using chemical isotopic data and tank model.