The use of benthic invertebrate production for the definition of ecologically acceptable flows in mountain rivers

Through benthic habitats occurrence, a link between secondary production and discharge is established, to be used for defining ecologically acceptable flows in mountain rivers. The presented procedure, named BENHFOR (Benthic Habitat FOR Optimum Flow Reckoning), supports the identification of optimum and minimum flow conditions for macro-invertebrate communities. Production values for the four habitats identified (pool, riffle, transition habitat and bedrock) and flow-production relationships for the whole community and for selected taxa are reported. Most taxa exhibit apparent increasing or decreasing trend of expected production with varying flows. For the mayfly E. helveticus, the production curve was split taking into account the observed developmental generations to sustain a more sensitive and seasonally adjusted discharge setting. Examples of optimum and minimum flow values for single taxa and community production are presented, based on notable points on the defined curves. The general applicability of the method is discussed.