ABSTRACT1. This study describes the development of an index for assessing stream habitats in northern Portugal at a variety of spatial scales and levels of perturbation. In developing the index, 86 environmental variables, including regional and local ones, were used to reflect the geomorphological characteristics, riverine habitat, and human activities occurring in each basin.2. Collections of benthic invertebrates were made at each sample site. To reflect the observed variation in assemblages, the streams were separated into two categories: the North-west catchments and the Douro catchments.3. Multivariate analysis techniques applied to the physical and biological data sets allowed the determination of the relative importance of local and regional environmental descriptors in the discrimination of the invertebrate assemblages.4. Successive statistical refinement procedures yielded 10 variables, all at the local scale. Variation along disturbance gradients allowed the development of a habitat index through scoring criteria that separated reference sites from stressed sites.5. The results indicate the reduced impact of catchment factors by a buffering influence probably resulting from the presence of a riparian corridor.
Abstract. This work represents an attempt to define a simple method to classify the relative degree of disturbance of sites in lotic systems on the basis of comparison of their faunistic composition with reference sites. Two ecotypes were selected in northern Portugal where benthic invertebrates were sampled in reaches with different levels of contamination. As a first stage, previous Geographic Information System information was used to define reference sites in each ecotype. Afterwards, multivariate techniques and non linear estimation models were combined to assess biological quality. This method allowed us to quantify sites according to increasing levels of contamination, after the probabilities of occurrence of taxa along a gradient of contamination taking into account the reference condition. The results suggest that this method is sensitive to organic pollution, easy to interpret, namely the species tolerance, and could be a good framework to establish regional rankings depending on the ecological impact of river sites.
The term "ecological integrity", which Anglo-Saxon authors also define as "river health" or "ecological condition", is frequently used in monitoring studies of water resources as a measure of the global condition of aquatic ecosystems.Although the first attempts to define the "health" of aquatic ecosystems have not reached consensus, Karr (1992) uses these three expressions interchangeably given the similitude of the components. Nevertheless, Suter (1993) insists that "health" is an inappropriate metaphor in an ecological context since it is a property only observable
ze crop production through irrigation. In these cases, the riverbed has been lowered, while riparian land is periodically cleared of trees and riverbank edges are cleaned (Aguiar et al., 2001).The objectives of this study carried out in the terminal part of the Mondego River (Centre of Portugal) were to characterize the macroinvertebrate communities and fish (abundance and
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