EN
Ecohydrology presumes that physical external variables have a major influence on the biological components of an ecosystem and vice versa. The relationships between physical factors and biological components may be useful tools in environmental management. It requires, however, that these relationships are known quantitatively. It is only possible through the development of a proper model for the ecosystem, because of the high complexity of the ecological network involved. A "proper model" is a model that can account for changes in species composition and adaptation, when the prevailing conditions are changed, i.e., a structurally dynamic model. The paper presents a model, that shows how a change from a constant out-flow rate from a reservoir to an out-flow rate that is purposely higher at the time of spring and summer bloom and at the time of spawning for planktivorous fish, is able to reduce the eutrophication level. The model presented in this paper considers only the phosphorus cycle, because phosphorus is presumed to be the limiting nutrient for phytoplankton growth. Two more ecohydrological examples that could be used quantitatively by use of a proper model are mentioned. The conclusion is, that ecohydrology offers possible and appropriate environmental management solutions but that a proper model for the considered cases is required to utilise ecohydrological possibilities quantitatively.