Defining a Disturbance Gradient in a Middle-Eastern River Basin.

A physical, chemical and biological characterization of river systems is needed to evaluate their ecological quality and support restoration programs. Herein, we describe an approach using water chemistry, physical structure and land use for identification of a disturbance gradient existing in the Karun River Basin. For this purpose, at each site, physical structure and physico-chemical data were collected once in each season for a total of 4 samples during the period (October 2018 - September 2019). Principal components analysis (PCA) of 17 variables identified five variables that were influential across all seasons: conductivity, total habitat score, stream morphology, clay & silt, and sand. Of the 54 sites, 14, 26 and 14 sites were classified as least, moderate and most disturbed sites, respectively. The metric Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa was used for validation of the classification. Results in different seasons showed that all the least disturbed sites (n=14) were significantly different from moderate and most disturbed sites (p < 0.01). In this study the validation process presented a good confirmation of a priori reference sites selection process, showing that the proposed criteria could be considered as appropriate tools for characterization of the existent disturbance gradient in the Karun River Basin.