Longitudinal connectivity in hydromorphological quality assessments of rivers. The ICF index : a river connectivity index and its application to Catalan rivers

摘要

The Water Framework Directive urges assessment of river continuity as an input for the evaluation of hydromorphological quality. The existence of transverse obstacles in river beds has serious ecological consequences because it blocks the natural flow of water, sediments and biota, and this is considered one of the major causes of declines in many continental fish species. The index of river connectivity (ICF, from the Catalan name Index de Connectivitat Fluvial) evaluates obstacle effects on fish movement alone and does not take into account other elements affected by the obstacles. However, it can be used as a complementary element in hydromorphological condition assessments. The index is based on comparison of obstacle and fish pass (if any) characteristics with the capabilities of the fishes potentially present in the considered river section to overcome the obstacle. In this study, we present a new version of the ICF improved from its earlier version that was tested by different consultants and research centres for several obstacles from 2006 to 2009. The new version of the ICF is divided into three blocks that encompass assessment of (1) the obstacle and (2) the fish pass (if any) as well as (3) the estimation of certain modulators. Finally, the ICF classifies connectivity into five levels from very good to bad depending on the degree of permeability for different fish groups. This new version of the ICF has been tested for 101 transverse obstacles in rivers in Catalonia (NE Iberian Peninsula) both with and without fish passes, obtaining representation of the five expected quality levels (from very good to bad), and it is considered coherent with the real permeability of the obstacles. Its ease of application compared to in situ measurements of fish movements and the detailed information recorded by the index make it a very useful tool for the diagnosis of the longitudinal connectivity of rivers and for guiding measures for hydromorphological quality improvement.