Acidification in nitrogen-saturated forested catchment

Continuous monitoring studies focused on nitrogen saturation were conducted at the Rolling Land Laboratory (RLL) of the forest experimental station lo cated in the Tama Hill region in Central Japan, Based on the nitrate concen tration 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 du e to N transformation (=([NH4+](th) - [NH4+](out)) - ([NO3-](th) - [NO3-](o ut))) amounted to 1.24 kmol(c) 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 tr ansformation accelerated base cation mobilization, Nevertheless, soil pH va lues at RLL did not decrease due to the abundance in base cations.