Adaptataions of benthic communities to ecopeaking in alpine rivers

Daily changes in physical and chemical water parameters (i.e., ecopeaking) can arise seasonally in natural conditions in kryal streams due to the summer daily glacial melt and consequent changes in runoff. Only few and specialized taxa living in such extreme habitats are adapted to such cyclic changes (e.g., Chironomidae Diamesinae and Simuliidae Prosimulinae). In regulated rivers, however, ecopeaking changes are sudden, occur once or more times per day, and span through the entire year, and are related to the releases from hydropower plants fed by high elevation and stratified reservoirs (i.e., the hydropeaking). The entire downstream benthic community is affected and, because large hydropower plants are usually at lower elevation, they affect communities which are not necessarily adapted to naturally-occurring changes. Hence, the effects of ecopeaking is very relevant. Changes in discharge (hydropeaking) and temperature (thermopeaking) have been proved to cause massive drift responses in benthic invertebrates in field and simulated conditions, whereas changes in turbidity, suspended sediments, conductivity and other chemical parameters have been less investigated. Rapid growth of the human population and economic development are tightly coupled with an increase in global energy demand, which is causing a current boom in hydropower dam construction (Zarfl et al., 2015). The effects on the biota already are, and will be, dramatic, and need to be fully understood. Simuliidae were selected as target taxon to assess the effect of ecopeaking on larval development and emergence. In fact, Simuliidae larvae are filter feeders, sensitive to alterations of solid transport and temperature and they permanently colonize floating substrates. Hence, they are easy to be semi-quantitatively collected upstream and downstream of the alteration source. Furthermore, the larvae have sclerotized head capsules which can be easily measured to assess life cycle parameters, and the pupal cases and exuviae remain fixed on the substrate after adult emergence and allow identification at the species level.