Short time-scale impacts of hydropeaking on benthic invertebrates in an Alpine stream (Trentino, Italy)

Abstract

a b s t r a c tThe impact of a single hydropeaking event was studied in the Alpine stream Noce Bianco. Four stations were selected, one upstream and three, respectively, at 0.25, 6, and 8 km downstream from a hydropower plant. We collected drifting invertebrates during a planned water release that increased the discharge 7-fold. At the onset of the hydropeaking wave the number of invertebrates lost from the riverbed per minute to the drift increased 9-fold at the first downstream station and the same effects propagated 8 km downstream. The drift was composed mainly of aquatic insect larvae (Chironomidae, Plecoptera, Ephemeroptera Baetidae, and Psychodidae, with Chironomidae as the most abundant taxon at all stations) and partly by larval and adult riparian insects, and by Oligochaeta, which were particularly abundant at the station 6 km downstream. We monitored drift for 30 min from the start of the water release: peaks in drifting invertebrates occurred within 5-10 min of the beginning of the hydropeaking wave, and most of the invertebrates were washed out within the first 15 min of the water release. The different timeframes were possibly due to habitat preferences (most of the taxa that increased in the drift at the arrival of the wave were associated with algae and organic debris, which were washed off quickly by the increase in discharge) and/or behavioral adaptations (other taxa initially resisted the shear stress and began to drift with a delay of 5-10 min). The temporal pattern and drift composition corresponded well with those reported in literature, and indicate that repeated high-flow events of similar magnitude cause considerable losses from benthic populations to drift.

Behavioral response of the freshwater cyclopoid copepod Eucyclops serrulatus to hydropeaking and thermopeaking in a laboratory flume

“…In the field measurements of Bruno et al (2010), peaks in drifting invertebrates occurred within 5-10 min after the beginning of the HP wave, and most of the invertebrates were washed out within the first 15 min of the water release. Drift abundance and composition returned to base-flow levels for most of the benthic taxa after 25 min.…”

“…It also explored the water column and performed very frequent incursions within the interstitial spaces of the sediment bed. Bruno et al (2010Bruno et al ( , 2016 link different timeframes for the beginning of the drift to taxon-specific habitat preferences and behavioral adaptations. In their measurements, most taxa with no morphological or behavioral adaptations to high flow velocity began to drift quickly after the arrival of the HP wave.…”

“…Baetis spp. and Chironomidae) are rapidly removed from the surface of the sediment (Gibbins et al 2005;Bruno et al 2010Bruno et al , 2016. Species with adaptations (e.g.…”

“…Passive drift has received much attention in the context of natural flooding events (reviewed in Naman et al 2016) but also and especially in relation to the release of water from reservoir hydroelectric power stations (e.g. Mochizuki et al 2006;Bruno et al 2010). It is indeed particularly prevalent in flow-regulated rivers due to the intermittent pattern of hydropower plant operation.…”

Contributions from limnology to reservoir management

“…Los embalses hidroeléctricos, a menudo causan importantes variaciones del caudal turbinado a escala diaria, e incluso semanal, en respuesta a los picos de demanda de consumo eléctrico (Prats et al, 2009), reduciendo el hábitat efectivo disponible y la productividad acuática (Poff et al, 1997). Esta alta variabilidad de los caudales hace aumentar el arrastre de los macroinvertebrados por la corriente (Bruno et al, 2010).…”