Elemental dynamics of a Japanese watershed with sugi (Cryptomeriajaponica) and hinoki (Chamaecyparisobtuse) plantations

Abstract

The roles of various components of the biogeochemical cycle in contributing to elemental loss or retention were evaluated in a Japanese watershed with 18-year-old plantations of sugi (Cryptomeriajaponica) and hinoki (Chamaecyparisobtusa). There was a large amount of foliar biomass (24.1 Mg•ha−1), which induced a large net increase of K+ (20.4 kg•ha−1•year−1) and consumption of H+ (0.26 kg•ha−1•year−1) in the canopy. Most of K+ in throughfall + stemflow was retained by vegetation increment. Although vegetation increment of N (33.9 kg N•ha−1•year−1) was larger than bulk precipitation N input (10.4 kg N•ha−1•year−1), high drainage loss of NO3− (13.6 kg N•ha−1•year−1) was observed. High N-mineralization and nitrification rates were suggested by high concentration of soil solution NO3− (315–434 μequiv.•L−1) and small forest floor N content. The high leaching rates of NO3− contributed to the high loss rates of Ca2+, the dominant cation in soil solution. The high N-mineralization and nitrification rates were likely due to the high temperature and moisture as well as the historical management of the watershed. High temperature and abundant moisture also accelerated chemical weathering of plagioclase, resulting in high drainage losses of HCO3−, Si, and Na+ and consumption of H+.