Hydrobiogeochemistry of forest ecosystems in Japan: major themes and research issues

Hydrobiogeochemical information on forested watersheds in the Japanese archipelago is reviewed to qualitatively summarize the major factors affecting the hydrology and biogeochemistry of this region. Major features that distinguish Japanese forest watersheds from those of north central Europe and the northeast United States generally include higher temperature, greater precipitation and steeper topography. There have been three major themes in hydrobiogeochemistry research on Japanese forest ecosystems: (1) investigations of nutrient cycles with particular emphasis on the establishment and maintenance of forest ecosystems; (2) evaluations of streamwater chemistry as an output from the forest ecosystem; and (3) hydrological studies using biogeochemical tracers. High precipitation inputs during the growing season affect the seasonality of the streamwater NO₃⁻ concentration, resulting in different temporal patterns than those generally found in north central Europe and the northeast United States. The high alkalinity and pH of Japanese surface waters is due to the rapid weathering of relatively young soils that are generated by steep hillslopes. Warm temperatures and elevated soil moisture enhance high rates of mineral weathering. Hydrological studies using biogeochemical tracers have shown that the steep topography contributes to the highly heterogeneous movement of water within Japanese catchments. Copyright © 2001 John Wiley & Sons, Ltd.