Prospects for simulation models in watershed studies

Any one who studies the watershed environments cannot ignore the strong link between terrestrial and freshwater ecosystems through material cycling. Simulation models of material and water cycling are useful tools not only for planning and practicing sustainable uses of forest and water resources and the adaptive management of forested watershed environments, but also for scientific researches. At the 70th annual meeting of the Japanese Society of Limnology (Kashihara, Osaka, September 2005), we discussed the validity and limitations of watershed simulation models in the section 'Watershed biogeochemistry: Simulation models for the watershed environment based on material cycling and hydrologic processes'. Biogeochemical and hydrologic models for forest, river and lake environments were introduced in the section. During the discussion, it was recognized that simulation models were valid and powerful for understanding and predicting environmental changes in the watershed. However, their applicability should be carefully checked when they would be used for regions under different climatic and environmental conditions. We also recognized that the introduction of the general characteristics of each model would be helpful to understand the significance of the simulation model in the limnological sciences. Titles of presentations were as follows: 1. Biogeochemical model in forest ecosystem; Application and problem of PnET model, 2. The influence of forest disturbance and examination of applying the PnET model for the long term influences, 3. Necessity for consideration on hydrological controls of biogeochemical cycling to develop a catchment scale ecosystem model, 4. Quantitative approach and problems of river hydrological simulation models, and 5. Biogeochemical model coupled with hydrodynamic model in lake environment. In this special issue, these five reviews are featured. Although each review is based on the presentation at the annual meeting, the content has been expanded and detailed.