River continuum and fish migration - going beyond the longitudinal river corridor in understanding ecological integrity

One of the central ecological problems of running water systems, which are subject to multiple uses and therefore suffer disproportionate damage worldwide in comparison to other ecosystems, is the fragmentation of the longitudinal corridor by weirs of hydroelectric power plants and other water engineering measures. Restoring previously interrupted migratory pathways of fishes using bypass systems is one potential approach, but simply passing fish generally tends to overestimate the 'feasibility' and ultimate success of amelioration strategies in the framework of river revitalisation projects. This chapter attempts to show that running waters are far more than mere longitudinal river corridors. Modern concepts of ecology describe running waters as complex, four-dimensional systems. While longitudinal river corridors represent an important dimension, they are merely one of numerous factors whose interactions define ecological integrity. The long-term preservation and sustainable utilisation of running water ecosystems can therefore only be achieved by fully considering all four dimensions that contribute to overall ecological integrity.