This work summarizes the results of an interdisciplinary research programme on "Hydrogeochemical Processes in the Hydrological Cycle within the Unsaturated Zones" (1982-1988). The quantitative transport and reaction models gained from this examination of the role of water from a chemical, biochemical and geologic-hydrological point of view, as well as their reactions in soils, provide a geoscientific contribution to ecological research.