Figure 2.

Values for the biomonitoring index IBMWP and associated biological quality (moderate, poor, bad) in two headwater intermittent rivers: (a) Cérvol and (b) Monlleó (Castelló, Spain). Although they may have disconnected pools for a short period during transitions between flowing and dry phases (i.e., Monlleó), both sites completely dry out during the dry season. The number of zero-flow days was assessed using temperature data loggers (Soria et al. 2020). Both sites are within the same official river typology (i.e., limestone rivers of Mediterranean lowland mountains) and, therefore, their quality is assessed using the same reference values. Neither site is exposed to significant anthropogenic pressures. Even when sampled during the flowing phase, as was indicated in standard protocols developed for perennial rivers, biological quality is underestimated for the site with the greatest distance to the nearest perennial site. Quality assessments are not performed when the river is dry. Data obtained from the TRivers Project.