Study on evolution of hydrobiogeochemistry with forest succession in humid temperate region

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In order to examine the various impacts of the forest growth on the acid buffering processes, hydrochemical observations were carried out in three different temperate catchments, each shares the same granitic bedrock , but having a forest different in growth conditions and soil depth. Hydrological processes in those watersheds were classified as; (1) the throughfall process, (2) soil infiltration process, (surface and subsurface soil layer infiltration sub-process, and the saturated groundwater transfer sub-process) and (3) the stream runoff process. The spatial distribution of pH, proton fluxes, and the changes of the proton producing and consuming processes were clarified. Specifically observed as changes accompanied by the vegetation growth were; (1) the decomposition of organic matters generated protons and (2) in addition to the chemical weathering , the cation exchange process started to consume protons in surface soil layer. (3) as a result, the proton production was relatively … More greater than consumption the surface soil layer, and some of the protons left unconsumed were transferred down to the subsurface soil layer and consumed. Specifically observed changes relating to soil depth were ; (1) pCOィイD22ィエD2 level at the groundwater is increased, as the soil layer is thicker. (2) As a result, pH after degassing is increased as the soil depth increased. Second, to quantify the impacts of forest vegetation on the acid buffering processes, hydrochemical observation data for two separate years were used to calculate the proton budgets in three small catchments, each consisting of the same granitic bedrock, but differing in vegetation development conditions. The increase in biological activity in the forested catchments, increased the net proton production by mineralization of organic matters and N transformation. In the forested catchments, the increase in transpiration reduced stream runoff. As a result, proton production by the dissociation of COィイD22ィエD2 decreased. When the estimated value for the cation uptake by vegetation was included in the proton budget, forest development increased the sum of these net proton productions by 2.3 to 4.0 times that of bare catchments. However, more than 96% of these proton productions were consumed by weathering and cation exchange within the catchments. It became apparent that the sum of these net proton productions by atmospheric input, N transformation, assimilation of cations, and dissociation of COィイD22ィエD2 is strongly affected by the amount of annual precipitation and annual runoff. The variance of proton production due to the fluctuation of annual precipitation almost equals the range of the increase in proton production by forest growth. Less