Development of a evaluation method of environmental effect on a forested ecosystem using a biogeochemical model based on stream-water hydrochemical processes

点击翻译按钮获取中文摘要

Studies on environmental changes in forested ecosystems caused by perturbations have been summarized. Among simulation models for biogeochemical material cyclings, we considered the applicability of the PnET model, which has been developed for northern American forests, for simulating the long-term environmental changes in forests in Japan. Observational results obtained in the forested watershed, where periodic logging has been conducted, were input to the PnET-CN model to simulate the water qualities of the streamwater. The model was well reconstructed the changes in the nitrate (NO_3^-) concentration among small catchments having different tree ages, although there were some difference in the level of concentrations between the observation and simulation. Effect of the logging on stream NO_3^- concentration can be found for 20 years after logging, coinciding with observations. It was suggested that logging rates up to 40% did not change the NO_3^- concentration level in the streamwa … More ter. The patterns of the long-term change in the woody biomass and the decrease in the leaf nitrogen content were successfully simulated. However, there were large gaps between observational and simulated values. It suggests that the careful setting of parameters included in the model should be done from viewpoints of water and nutrient conditions and the development of the rizosphere. Forest renewal and hydrologic processes should be taken into considerations to improve the simulation results.In order to clarify the relationship between stream water qualities and watershed environmental conditions, we conducted the nationwide survey on the stream hydrochemistry in Japan. We collected stream waters from more than 1270 sites and analyzed the ionic concentrations. It was suggested that the stream NO_3^- concentration was largely governed by the atmospheric nitrogen deposition to the watershed. From the comparison with previous survey in 1950's, the stream NO_3^- concentration in Japan increased during 50 years. Geologic characteristics in the watershed affected the phosphorus (PO_4^<3->) concentration. Less