3 Materials and Methods
3.1 Materials and Methods Benthic diatom samples were taken yearly at the Ebro river basin, monthly for the experimental setup and bi-monthly at the temporary river sites (Table 2). For the period investigated in this work, different persons took care of sampling and preparation. The sampling followed the European and Spanish norm (AENOR 2014, 2004) and the Ebro river sampling protocol (Cambra et al. 2005) . Thus, diatom communities were scrubbed with either a toothbrush or knife from five randomly collected stones from the river bottom (Kelly et al. 1998) . The resulting scrub was put into a mixture of river water and either 4 % formaldehyde (until 2012) or 70 % ethanol. In the laboratory, an aliquot of the samples was digested according to the 30% hydrogen peroxide (110 ºC for 12 h)-hydrochloric acid (1M) protocol and washed with distilled water (Cambra et al. 2005) . From the suspension, one drop was dried on a coverslip, which was subsequently mounted on a microscopic slid