The present study aims to develop river ecosystem indicators, in particular for the River Rhine, on the basis of theoretical concepts describing natural rivers. The study includes river ecology concepts on zonation, stream hydraulics, river continuum, nutrient spiralling, serial discontinuity, flood pulse, riverine productivity and catchment hierarchy. The abiotic steering variables describing the hydrology, geomorphology and water quality, act as a template for ecosystem functioning. Functional processes are characterized by the flux of matter, which is affected by input, processing and retention of organic matter and nutrients. Spatial and temporal variation of input and retention of matter and the flow along the length of the river cause shifts in species distribution. These are reflected in gradients of macroinvertebrates and zonation of fish and benthic fauna, which form a dominant structural characteristic of the river ecosystem.
Indicators proposed are retention of matter as an indicator for the functional characteristics and zonation of species as an indicator for the structural characteristics of the river ecosystem. Present river ecosystems are far from undisturbed. To allow efficient management of the river ecosystem, indicators and variables are required that reflect the cause-effect chain of human disturbance. River ecologists have developed a more spatially integrated and interdisciplinary view on rivers. Accordingly, the design, implementation and ecological assessment of monitoring programmes should reflect such an integrated spatial view. This means that a set of water quality, hydrological, geomorphological and ecological variables should be measured on a catchment scale, and that resulting data should be related to each other. Finally, this study presents some recommendations for monitoring, in particular for the Rhine monitoring programme.