Spatial and seasonal distribution of invertebrates in Northern Apennine rheocrene springs

Four perennial rheocrene springs located between 919 and 1252 m a.s.l. on substrata characterized by different lithologies were studied. Water samples and invertebrates were collected seasonally for one year. The crenic fauna was collected using three sampling techniques: moss washing, drift tubes and benthic traps. Each sampling technique was particularly efficient for collecting specific taxa typical of the different habitats (crenophilous crustaceans and crenoxenic benthic insects were dominant in benthic traps and moss; crenophilic, stygophilic and stygobiotic crustaceans in drift tubes). A total of 3,284 invertebrates belonging to 54 taxa were collected. Ostracoda, Harpacticoida, and Diptera were the most abundant taxa. Species assemblages collected at each spring, in each season, in traps and mosses, differed among springs, and, based on invertebrate assemblages, the ordination of the investigated springs did not correspond to that based on environmental parameters. Of the environmental variables only pH and temperature explained the diversity pattern. Assemblages collected from different habitats also differed: benthic traps collected mainly Chironomidae, Ostracoda, other Diptera, crenophilous Harpacticoida, and Gastropoda; in moss assemblages, the fauna was mostly represented by crenophilic Harpacticoida, Ostracoda, Plecoptera, Chironomidae. Finally, the groundwater assemblages, collected with drift tubes, were dominated by crenophilous Harpacticoida, Chironomidae and Plecoptera. Variation in number of taxa over time was observed in traps and moss samples, whereas drift tubes showed no seasonality. Meiofauna (i.e., permanent meiofauna, represented by Nematoda, Copepoda, Ostracoda, and Hydrachnidia, and temporary meiofauna, represented by early instars of insect larvae) dominated all habitats, probably because of constant flow and favourable habitats such as moss. The presence of mosses was a factor that increased the species diversity of the investigated springs; drift tubes allowed most of the stygobiotic taxa to be collected, although this technique did not necessarily increase the total number of taxa collected. In addition to the array of habitats, other factors, such as geology, might influence the structure of invertebrate communities. The diversity of the investigated springs was strictly dependent on the presence of different microhabitats and local environmental conditions

An ecosystem service approach to license new run of the river hydropower plants

Freshwater ecosystems provide several services (ES) to society. Hydropower production is one of the most relevant ES supported by Alpine rivers, and it is often in conflict with other river uses and services. Recently, the demand by local authorities, public or private agencies for new small hydropower plants have been increasing, and new conflicts have been arousing. We propose an approach to model the alterations of selected ES which integrates hydrological and habitat models and evaluates possible variations of the selected ES under different withdrawal scenarios. The case-study is the Noce River, a gravel-bed river in the Italian Alps (Trentino, North East Italy) which is subject to hydropeaking. We selected four ES: habitat for juvenile and adult marble trout as biodiversity proxy, rafting as recreational services, and small hydropower production as provisioning service. We evaluated the variations of these services for maximum and no hydropower production, chosen as different boundary conditions. Moreover, we simulated the presence of four new different small hydropower plants with increasing withdrawals. Large hydropower is the key driver, affecting all the selected ES. Small hydropower decreases the potential for rafting up to 64%, while it is often negligible for other services

Multiple drift responses of benthic invertebrates to hydropeaking waves

Sudden instream releases of hypolimnetic water from hydropower plants (i.e., hydropeaking) can cause abrupt temperature variations (i.e., thermopeaking), typically on a daily basis. The propagation of the discharge and thermal waves are asynchronous, causing the benthic community to undergo two distinct but consecutive impacts. Invertebrates are known to respond to sudden increases in discharge with catastrophic drift, and recently have been shown to respond to sudden changes of temperature with drift, which is probably behavioral. Due to the decoupling of the discharge and thermal waves, catastrophic and behavioral drift can occur as distinct events. We analyzed the induction of drift in benthic invertebrates caused by a hydropeaking wave followed by a thermopeaking wave, in two open air flumes directly fed by an Alpine stream. The slight but abrupt increase in discharge caused a maximum 28 and 24-fold peak increases in drift in the two flumes, and the abrupt decrease in temperature caused an increase of 36 and 198-fold in the same flumes. In both flumes drift propensity increased during hydropeaking and thermopeaking simulations, and was higher during the latter

Stream ecology in Alpine streams: does management overwhelm climate change?

Flow and temperature regimes are the main driving forces influencing habitat structure and ecological functions in lotic ecosystems. The five major components of flow regime: magnitude, duration, frequency, timing and rate of change regulate the ecological processes in river ecosystems. The natural temperature regimes of rivers provide thermal cues that stimulate responses in many aquatic species, and affect many physical and chemical processes which play a crucial role for community composition of stream macroinvertebrate communities and for individual species. In Alpine streams, the presence of hydropower plants can significantly alter the hydrological and thermal regimes.Water is abstracted from headwaters, stored in artificial, high elevation reservoirs, used to produce hydropower and finally released downstream in the form of “hydropeaking” (i.e. sharp releases of water which, in Italian rivers, can increase the discharge of 10x the baseflow). On a yearly time scale, hydropower production has been impacting the temperature and flow regime of most Italian Alpine rivers from the middle of the last century. In general, a progressive flattening in the hydrograph occurred. The alterations in temperature are represented by a decrease of water temperatures from the beginning of spring to the end of summer downstream of the point where hypolimnetic waters are released, and a warming of the receiving waterbody from the beginning of autumn to early spring. Examples from rivers of different typology are presented to show the alterations of the thermal and discharge regime, and their ecological effects, based on the results of our research. In Alpine streams, the impacts of climate change will sum to those of management. Because the hydrological cycle will be enhanced under warmer climatic conditions, the current distribution, seasonality, and amount of precipitation will undergo significant changes. Due to the forecasted glacier retreat, in glacierized basins a temporal shift of discharge peaks due to increase of snowmelt vs glaciermelt towards early summer instead than mid summer will occur; as a consequence, there will be an increase of water to be abstracted and stored in reservoirs in the short term, but less water in the long term when smaller glaciers will disappear. Due to reduced snowfall, more water will be needed for production of artificial snow. In view of the forecasted climate change and consequent increase in water demand in the Alps, it is crucial to direct Alpine research to a better understanding of the changes occurring in freshwater ecosystems in order to produce new ecologically sustainable management recommendations

Settling distances of benthic invertebrates in a sediment mobilization simulation in semi-natural flumes

Drift time and distance depend on the ability of the drifting invertebrates to alter their body posture or by swimming, and these behaviours may change according to the local hydraulic environment, resulting in different distances travelled before exiting the drift. Such drift and settlement mediated invertebrate movement determine dispersal processes and ultimately generates distribution patterns within streams. We conducted an experiment in an open-air, artificial flume system directly fed by an Alpine stream, where we disturbed the sediment in the flumes, inducing catastrophic drift in the benthic community, and then assessed the settlement distances of benthic invertebrates. For each flume, we collected drift samples by disturbing the substrate at 1.5 m intervals, at increasing distance from the downstream end, for a total of 7 disturbances and a maximum settling distance of 10 m in each flume, with five replicates (i.e., five flumes) for each disturbance. The disturbances induced a massive catastrophic drift in Ephemeroptera, Plecoptera and Trichoptera, always higher than the behaviourally-occurring basedrift. The Settling Index calculated over the total drift collected at each distance increased with increasing distance, and after 10 m, 90% of the drifting animals had settled. Evenness and taxa richness progressively decrease with increasing settling distance. All drifting taxa were represented mainly by young instars. We used the drift collected at 1 m from the disturbance to standardize the remaining samples, based on the assumption that 1 m is not a distance long enough to allow animals to settle at that water velocity We calculated the percentage of possible drifters which settled by computing a Settling Index for each taxon. The drifting taxa listed by decreasing Settling Index scores were Epeorus sp., Rhithrogena semicolorata, Isoperla spp., Sericostoma spp., Ecdyonurus spp., Nemoura spp., Leuctra spp., Baetis spp., Hydropsyche spp., Rhyacophila spp. We have shown, in accordance with numerous other studies, that entrained EPT nymphs travel only short distances before returning to the substratum, and that the actual distance travelled while drifting and the total time spent in drift varies between species. The results of this study can provide suggestions to assess taxon-specific availability to colonization which generates distribution patterns within streams and, on a smaller scale (i.e., flume simulations), our results can be extrapolated to other studies conducted in artificial flumes, or to support evidences from field studies