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Abstract
Continuous monitoring studies focused on nitrogen saturation were conducted at the Rolling Land Laboratory (RLL) of the forest experimental station located in the Tama Hill region in Central Japan. Based on the nitrate concentration in stream water, it was estimated that the forest ecosystems at RLL could be classified into Stage 2 of nitrogen saturation. The stream water pH decreased when the nitrate concentration increased. Proton production due to N transformation (= ([NH4 +]th-[NH4 +]out)-([N03 -]th-[N03 -]out) amounted to 1.24 kmolc ha-1 y-1 in 1991–1992, a value 1.5 times as high as the total atmospheric proton input. Sulfate adsorption buffered the impact of the acid load. Protons were mainly consumed by ion exchange with base cations and weathering processes. Both acidic deposition and N transformation accelerated base cation mobilization. Nevertheless, soil pH values at RLL did not decrease due to the abundance in base cations.
