ABSTRACT
Natural forested watersheds are prototypes of ecosystems. They have a relatively well-defined boundary, closed cycles for fluxes of elements, contain a collection of species of all kinds of spatial sizes, and are of important human concern as timber source and drinking water supply. The convincing success of deterministic models in physics and other "hard" sciences has let ecosystem researchers to follow similar lines, especially in the context of transport simulation. Appropriate simplifications of the Navier-Stokes equation have been developed for the description of water movement in soils and other porous media, and the movement of solutes with convection-diffusion models. The selection of appropriate measures to quantify ecosystem input and output is primarily dictated by the length and quality of the available data. Some of the monitored data, especially related to hydrology, are taken since decades. Short-term fluctuations can be investigated through information-theoretic measures.
