Abstract

During the 20th century, environmental problems have increased from sewage discharge in the first decennia towards climate change today. An increase in scale of threats implies an increase in scale of management and assessment. Successively, physico-chemical, biological and ecological assessment evolved but failed to stop deterioration. The development in techniques runs parallel to the evolution in assessment. Eight major groups of assessment techniques are distinguished: indices (saprobic, diversity, biotic), multimetrics and rapid techniques, physico-ecological, catchment scale, ecosystem components, assemblage/community, process, and non-taxonomic assessment. An increasing refinement is observed in objectives, measures and complexity, and a decreasing one in levels of scale, stream type and, more often, taxonomy. The applied algorithms were typically restricted to single summary measures. Multivariate analysis was introduced only recently. Assessment can do without a reference condition. Still, this condition is often used in assessment. Therefore, the role of the reference is discussed and it is concluded that, if used, it needs to be defined strictly. The role of nine concepts of lotic ecology in assessment is studied. Two major groups of concepts are distinguished. One is related to catchment-scale functioning of streams and the other to instream habitat-related processes and biodiversity. The 5-S-Model, a frame that divides the stream ecosystem into five major components: system conditions, stream hydrology, structures, substances and species (Verdonschot et al., 1998: The 5-S-Model, an integrated approach for stream rehabilitation. In H.O. Hansen & B.L. Madsen, River Restoration '96, Session lectures proceedings. National Environmental Research Institute, Denmark, International Conference arranged by the European Centre for River Restoration: 36–44), is a first attempt to comprise this knowledge in management. Finally, integrated ecological assessment is defined. It is based on three major approaches: an ecological typology approach, an ecological catchment approach and a societal approach. Ecological typology implies a nested multiple parameter approach based on regional ecological stream typology where types are scaled and different taxonomic groups are incorporated. Ecological typology sets the ecological demands necessary to make management sustainable. The ecological catchment approach implies a nested multiple scale approach which couples natural and anthropogenic features and dynamics of the catchment both in space and time. This approach sets the conditions within the catchment to facilitate sustainable catchment management. The societal approach adds human activities to the first two. It couples ecological demands and anthropogenic uses and supports those user choices that make management sustainable. The application of these three approaches is initiated to enable sustainable catchment management.