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NITROGEN SATURATION IN JAPANESE FORESTED WATERSHEDS
Author(s) -
Ohrui Kiyokazu,
Mitchell Myron J.
Publication year - 1997
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(1997)007[0391:nsijfw]2.0.co;2
Subject(s) - cryptomeria , environmental science , chamaecyparis , biogeochemistry , hydrology (agriculture) , watershed , hardwood , nitrogen , precipitation , vegetation (pathology) , ecology , japonica , biology , chemistry , geology , botany , geography , geotechnical engineering , organic chemistry , machine learning , computer science , medicine , pathology , meteorology
Biogeochemistry of nitrogen was evaluated in a series of small watersheds in Gunma Prefecture, 100 km northwest of Tokyo in Japan. The forest vegetation ranged in age from 7 to 86 yr and included conifer plantations and naturally regenerated hardwoods. In a watershed with 24‐yr‐old stands of sugi ( Cryptomeria japonica ) and hinoki ( Chamaecyparis obtusa ), stream water NO 3 − concentrations were lower (21 μmol/L) than watersheds composed of 7‐, 84‐, and 86‐yr‐old stands (62, 64, and 100 μmol/L, respectively). These differences among watersheds were mostly attributable to differences in the increments of N by forest vegetation. The absence of seasonal variation of stream NO 3 − concentration in watersheds with either coniferous or hardwood forests suggests that N availability was in excess of biotic demands during all seasons. Over 6 yr, inorganic N output by stream water (13.5 kg N·ha −1 ·yr −1 ) exceeded N input as bulk precipitation (10.5 kg N·ha −1 ·yr −1 ) in an 86‐yr‐old coniferous stand. The high N output was related to high N input by precipitation, high mineralization rate, and low N wood increment. The high NO 3 − concentrations, absence of seasonal variation, and high loss rates of N through drainage waters together suggest that some Japanese watersheds are exhibiting “nitrogen saturation.”