Relevant variables to predict macrophyte communities in running waters

In both predictive theoretical and empirical models for aquatic plant communities in running waters, the development and competition are many times explained in terms of nutrients. Minerals necessary for growth are generally not assumed to be limiting, although they influence the important pH-value. At the same time it is known that factors such as oxygen-concentration, solar energy, salinity, dimension of the system and soil characteristics (including river sediments) influence the development of the community, and should be considered in modelling. Effects of water quantity and water quality on macrophytes are reviewed. These conditions are caused by processes in the landscape, characterised by a set of nested variables which explain the distribution of macrophyte species and communities. Relevant variables are described and grouped on three scales: regional, local and site conditions. Case studies with direct and indirect gradient analysis are presented. Statistical tests (stepwise regression with forward selection) reveal that each species distribution is explained by a characteristic set of relevant variables, ranging from soil type and dimension of the system, to nutrient and salinity concentration.