Effects of flow events and nutrient addition on stream periphyton and macroinvertebrates: an experimental study using flumes

Abstract

-We used flume experiments to study the effects of a temporary increase in stream flow on macroinvertebrates, leaf litter breakdown and soft-bodied benthic algae; both as a single stressor and eventually in combination with an increase in nutrient supply. In order to understand how well the flumes reflected the nearby stream ecosystem, we compared species composition of macroinvertebrates and benthic algae between the flumes and the nearby stream from which the flumes were supplied with water. As single stressors, nutrient addition and an increased flow velocity from 1.3 to 2.8 cm s À 1 lead to an increase in the biomass of benthic algae, likely reflecting an improved transfer of nutrients into algal patches. However, the combined effect of flow and nutrient addition was smaller than the sum of both individual effects, likely because an increased biomass also was more susceptible to scouring. We found differences in macroinvertebrate and benthic algal taxon identity and abundance between stream and flumes. Since biodiversity is assumed to stabilize ecological functioning in response to disturbances and variation, we conclude that care should be taken in applying results from small scale experiments to stream ecosystems. Nous avons utilisé des expériences en canaux pour étudier les effets d'une augmentation temporaire du débit sur les macroinvertébrés, la dégradation de la litière foliaire et les algues benthiques à corps mou, à la fois comme stresseur unique et éventuellement en combinaison avec une augmentation de l'apport en éléments nutritifs. Afin de comprendre dans quelle mesure les canaux reflétaient bien l'écosystème du cours d'eau voisin, nous avons comparé la composition spécifique des macroinvertébrés et des algues benthiques entre les canaux et le cours d'eau voisin qui alimentait les canaux en eau. En tant que stresseurs uniques, l'ajout de nutriments et une vitesse d'écoulement accrue de 1,3 à 2,8 cm s À 1 entraînent une augmentation de la biomasse des algues benthiques, ce qui reflète probablement un meilleur transfert des nutriments dans le périphyton algal. Toutefois, l'effet combiné du débit et de l'adjonction de nutriments était plus faible que la somme des deux effets individuels, probablement parce qu'une biomasse accrue était aussi plus susceptible de se décoller. Nous avons trouvé des différences dans l'identité et l'abondance des taxons de macroinvertébrés et des taxons d'algues benthiques entre le cours d'eau et les canaux. Puisque la biodiversité est supposée stabiliser le fonctionnement écologique en réponse aux perturbations et aux variations, nous concluons qu'il faut faire preuve de prudence dans l'application aux écosystèmes des cours d'eau des résultats d'expériences à petite échelle.

Unravelling the effect of flow regime on macroinvertebrates and benthic algae in regulated versus unregulated streams

“…However, exploitation of freshwater resources such as industrial abstractions, hydropower generation, and drinking water supply has significantly altered natural flow dynamics across the globe (Poff et al, ); 37% of European rivers are affected by flow regulation (http://www.ecologic.eu/11663) and, in Norway, where hydropower provides >95% of the total electricity generated, more than two thirds of river basins are affected by hydromorphological alteration (http://www.nve.no). Understanding the effects of flow alteration on aquatic ecology is crucial for the sustainable management of regulated river systems, but linking indicators of hydrological change to ecology is not straightforward because (a) properly replicated and controlled experiments are rarely possible in practice in fluvial ecosystems (Richter et al, ), (b) species assemblages in experimental flumes often differ from the assemblages in adjacent watercourses, raising questions on the relevance of flume experiments (Bækkelie, Schneider, Hagman, & Petrin, ), and (c) field data may reflect the effects of correlated variables rather than the effects of the variables of interest.…”

“…alteration (www.nve.no). Understanding the effects of flow alteration on aquatic ecology is crucial for the sustainable management of regulated river systems, but linking indicators of hydrological change to ecology is not straightforward because (a) properly replicated and controlled experiments are rarely possible in practice in fluvial ecosystems , (b) species assemblages in experimental flumes often differ from the assemblages in adjacent watercourses, raising questions on the relevance of flume experiments (Baekkelie, Schneider, Hagman, & Petrin, 2017), and (c) field data may reflect the effects of correlated variables rather than the effects of the variables of interest.…”

Interactive effects of discharge reduction and fine sediments on stream biofilm metabolism

“…The literature shows contrasting effects of water discharge on biofilms. Some studies reported no response for algal biomass [54][55][56] as well as for metabolism [14,54], whereas others showed that algal biomass decreased both above and below optimum velocities, a fact that would be explained by shear stress at high velocities, by nutrient limitation at low ones. This is the type of response reported by Biggs and Stokseth [57] where the algal biomass peaked at a velocity of 30 cm s -1 .…”

Application of Flow-Ecology Analysis to Inform Prioritization for Stream Restoration and Management Actions

“…However, for flow management and restoration to be fully successful, it is important to consider the effects of other influencing factors at various spatial scales (King et al, 2016;Verdonschot et al, 2016). Such a task is complicated by interactive effects that modify the impact of confounding factors (Folt et al, 1999), such as habitat complexity dampening the strength of temperature effects (Scrine et al, 2017) or a combined effect of flow velocity and increased nutrient concentrations being smaller than the individual impact (Baekkelie et al, 2017).…”