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Criteria for the selection of reference conditions in the Mediterranean rivers. Results of the GUADALMED project

Abstract:

The water Frame Directive (WFD) establishes the need to define reference conditions in order to determine the ecological status of all the test sites from each ecotype. Several criteria may be used to select reference conditions. In the GUADALMED project, five localities per basin were selected a priori according to the experience of experts, which is one of the criteria considered in the WFD. Results showed that in 72% of selected reference conditions, water quality was poor (IBMWP<100 in all sampled seasons) and the riparian vegetation, altered (QBR<75). Consequently, we established a set of new criteria for appropriate selection of reference conditions for natural riparian vegetation status, natural basin uses, unaltered fluvial channel, absence of reservoirs, diverse river habitat conditions and low nutrient concentrations. A few sites conform to all these criteria, whereas others may comply when a site upstream or downstream is considered instead, or after restoration techniques are applied. Results obtained were compared with the previously established System B typologies. For some ecotypes, no reference sites were found occasionally because of the difficulty in finding given basin or river reach characteristics. In these cases, a "Maximum Ecological Potential" was used instead of the reference condition. When the criteria established were compared with the biological indices across seasons for each site, a positive and significant relationship was found between all criteria and the IBMWP and QBR indices. Here, we present a set of criteria for use as a general framework to select and validate reference condition during the second phase of the project GUADALMED. © Asociación Española de Limnología.