Different scales of analysis in classifying streams: from a multimetric towards an integrate system approach.

Abstract

Two different approaches to define the ecological status of several catchments in NW Portugal are compared. At a coarser scale, whole stream networks were classified using GIS according to variables related to: a) biotic indicators (native and exotic fish species, benthic biotic index and characteristics of the riparian corridor); b) chemical indicators of contamination (industrial and urban organic loads and water quality). This methodology was preceded by a typological classification, so that ecological status could be determined separately for each of the physical units within a watercourse. At a lower scale, sites were categorized on the basis of the invertebrate fauna and the most relevant metrics were selected through multivariate procedures. These two methods can be seen as complementary and they produced similar indications of disturbance levels in spite of different assessment techniques and distinct space scales of analysis. Using the first method (assisted by GIS), we can identify the main typological gradients and the location of the most pristine segments. Relaying on the classification displayed by this method at the catchment scale, the second method one enables us to define with accuracy the sampling sites and the most convenient metrics for biomonitoring in river health assessment systems.