Responses of benthic invertebrates to repeated hydropeaking in semi‐natural flume simulations

Abstract

We assessed the effects of repeated hydropeaking over five consecutive days on the zoobenthic community by manipulating discharge in five experimental flumes directly fed by an Alpine stream. Treatment consisted of two different hydropeaking intensities which increased discharge two‐ and threefold from baseflow and lasted for 5 h each day. The resulting sudden changes in flow directly affected benthic invertebrates through the induction of catastrophic drift as a direct response to high (hydropeaking) flow conditions, and of behavioural drift in the low, baseflow conditions (at the conclusion of each hydropeaking event) for some taxa. We observed: an initial strong peak in catastrophic drift within the first 3 min of increased discharge, followed by a decreased drift rate throughout the following hours of the experiment; a strong response in the first day of the simulation, with successive days having substantially decreased drift; taxa‐specific responses over the short and long‐time scales: least‐resistant taxa (i.e. Baetis spp.) were removed via the initial catastrophic drift, while more resistant taxa began to behaviourally drift later in each hydropeak (i.e. Simuliidae). Peaks in drift rates corresponded to the initial removal of CPOM which, during low flows, provided habitat and food resource for a high number of individuals and taxa. Quantification of drift responses over time scales larger than the single hydropeaking event underlines the relevance of the typical intermittency and repetition frequency as a stress factor for benthic communities, and that the response to hydropeaking is closely related to the time elapsed since the last perturbation. Copyright © 2015 John Wiley & Sons, Ltd.

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

“…The flume system described in this study was successfully used to assess macrobenthos drift responses in previous simulations (Carolli et al, 2012, Bruno et al, 2013, 2016. Our flumes have the advantage of being freely colonized by the benthic fauna from the pristine Fersina Stream via incoming drift from upstream (mainly) and egg deposition by adult (likely occurring, but never observed directly), and thus they approximately represent the benthic assemblages present in the area.…”

“…In real case scenarios (such as floods, hydropeaking events) the disturbance is, however, diffuse. In previous experiments we conducted in the same flume system (Carolli et al, 2012;Bruno et al, 2013Bruno et al, , 2016, we simulated hydropeaking or thermopeaking waves which elicited a drift response from the benthos occupying the entire flume substrate. Hence, the results of this and our previous studies cannot be compared.…”

“…The flumes are filled to the same depth with two layers of cobbles of approximately 10 cm diameter, and a deposited fine layer of silt/sand/gravel has collected around the stones. , from the beginning of April 2013 for other simulations (Bruno et al, 2016), and reset on September 10 th , and the flumes left undisturbed until the experiment day, occurring on 22 nd October 2013.…”

“…Today, experimental flumes of different typology have become a common tool to study the responses of biological communities to physical, chemical, hydrological manipulations, using behavioral and catastrophic drift as the measured response and based on the hypothesis that any invertebrate showing an immediate avoidance or displace-N o n -c o m m e r c i a l u s e o n l y ment reaction would rapidly drift (Holomuzki and Biggs, 2000;Imbert and Perry, 2000;Suren and Jowett, 2001;Mochizuki et al, 2006;Carolli et al, 2012;Fenoglio et al, 2013;Bruno et al, 2013Bruno et al, , 2016. Although drift catches in these simulations were often high, it is difficult to assess the significance of these responses, since if a high proportion of the benthos enters the drift for a short period of time, the drifting invertebrates may have originated from the area immediately downstream from the disturbance and could have returned rapidly to the benthos and thus not have been caught.…”

Energetic Consequences of Stranding of Juvenile Atlantic Salmon (Salmo salar L.)

“…Final fish density did not account for the differences, but selective mortality could have increased mean final body mass (as was discussed above for final body length). The fluctuations in water level may also induce catastrophic drift in invertebrates [34] and thus affected the fish mass change in the experimental channels less nega- Lipid stores in juvenile salmonids seem to be important for winter survival, and relatively small increases in metabolism may have severe consequences (e.g.…”