Many streams on Kureha Hill, Japan, suffer from acidification caused by nitrogen saturation. At the Hyakumakidani watershed, one of the streams on Kureha Hill, the nitrogen budget is such that the input nitrogen is much higher than the output nitrogen. This fact indicates that the excess nitrogen leached to the stream water has sources within the watershed.
The purpose of the current study was to identify the source of nitrogen leached into the streams.
Incubation experiments of soils and soil cores taken from several different horizons of the Hyakumakidani watershed were conducted to investigate the location at where the nitrate was generated in terms of the soil layers.
In the incubation experiment of soils, the soil taken from the A horizon showed the highest nitrification rate, while the soil taken from the B horizon and the C horizon showed much lower rates.
I n the incubation experiments of soil cores, NH
4Cl solutions were dropped into the cores to simulate rainfall. The nitrate concentration of the drainage water from the A horizon core had a much higher concentration of nitrate than the NH
4Cl solutions, while the nitrate concentration of the drainage water from the B horizon core was nearly equal to that of the NH
4Cl solutions.
The results of these experiments indicate that the source of nitrate was within the A horizon.
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