Development of a multimetric benthic macroinvertebrate index for assessing the ecological condition of Basque streams (north of Spain)

Multimetric indices based on biological communities for the assessment of the ecological status of streams and rivers have recently been developed for many regions. However, local differences in reference conditions, human impacts and biological communities make developing suitable indices for different regions of the world necessary. Thus, our goal was to develop and validate a multimetric index based on macroinvertebrates to evaluate the ecological status of streams from the Basque Country (north Spain). For this, 22 lowland calcareous streams (7 reference and 15 disturbed) were monitored from 1993 to 2005. At each study site, a stress level was calculated based on human impacts. Fifty-three macroinvertebrate metrics were tested for their capability to discern stress level. Our multimetric index was calculated as the mean of six metrics - genus richness, IBMWP, abundance of Sel_EPTD, abundance of Sel_ETD', family richness of Sel_ETD and family richness of EPT. The index was split into five ecological status classes, ranging from 0 (bad ecological status) to 1 (high ecological status). This index was validated in 231 study sites in 108 streams of six different typologies, demonstrating suitability for application in biomonitoring and assessment studies in Basque streams.