Suggestions for diatom-based monitoring in intermittent streams

Abstract

-Over the last decades, river lentification processes and droughts have been dramatically spreading worldwide, due to global and local drastic changes due to human activities. Under this scenario, the evaluation of physical disturbance caused by intermittency and droughts has become more and more relevant. In this research, we compare samples collected in Mediterranean streams following both traditional and experimental approaches with the aim of understanding if diatom indices calculated from a new sampling strategy could provide additional information for the physical disturbance assessment. Moreover, we also evaluated the response of functional metrics. Our results demonstrated that even though an enhanced sampling method better reflects hydrological disturbance than the traditional one, diatom indices do not detect it. Conversely, functional traits proved to be important metrics for the hydrological disturbance assessment. In particular, benthic diatom chlorophyll a showed significantly lower values in sections more subject to droughts. With respect to ecological guilds, the motile taxa proved to be linked to depositional areas, which resulted important microhabitats (MHs) to be explored in rivers affected by lentification. Including different MHs in the sampling process improves the information we can obtain from the analysis of the diatom community and presents important implications in documenting species distribution and autecology.Keywords: diatom indices / functional metrics / hydrological disturbance / intermittency / Mediterranean streams Résumé -Suggestions pour la biosurveillance avec les diatomées benthiques dans les rivières intermittentes. Au cours des dernières décennies, les processus de ralentissement des rivières et les sécheresses ont été considérablement répandus dans le monde entier, en raison de changements drastiques globaux et locaux dûs aux activités humaines. Selon ce scénario, l'évaluation des perturbations physiques causées par intermittence et les sécheresses est devenue de plus en plus pertinente. Dans cette recherche, nous comparons les échantillons prélevés dans des rivières méditerranéennes suivant des approches traditionnelles et expérimentales dans le but de comprendre si les indices diatomées calculés à partir d'une nouvelle stratégie d'échantillonnage pourraient fournir des informations supplémentaires pour l'évaluation des perturbations physiques. De plus, nous avons également évalué la réponse des paramètres fonctionnels. Nos résultats ont montré que, même si une méthode d'échantillonnage améliorée reflète mieux les perturbations hydrologiques que la méthode traditionnelle, les indices diatomées ne les détectent pas. À l'inverse, les traits fonctionnels se sont avérés être des paramètres importants pour l'évaluation des perturbations hydrologiques. En particulier, la chlorophylle a des diatomées benthiques a montré des valeurs significativement plus faibles dans les sections plus exposées à la sécheresse. En ce qui concerne les guildes écologiques, les taxons mo...

Environmental and spatial factors drive diatom species distribution in Alpine streams: Implications for biomonitoring

“…priority effects) or individual spillover from upstream populations (i.e. mass effect), the analysis of the functional profile of diatom communities supports the role of dispersal limitation because the motile guild is dominant in impacted sites, which has been observed to be associated with both hydrological (Elias et al 2015;Falasco et al 2016) and morphological (Smucker and Vis, 2010;Bona et al 2016) alterations. Our results therefore suggest that considering diatom response not only to trophic conditions but also to physical alterations is crucial in biomonitoring programs.…”

Modelling diatom life forms and ecological guilds for river biomonitoring

“…For instance, high light exposure causes the formation of complex biofilms with multiple layers and enhances the competitive advantage of the MG in nutrient consumption . Diatom communities also change with geology and river typology (Rimet, 2009;Tison et al, 2005), current velocity (Steinman and McIntire, 1986), predation (Feminella and Hawkins, 1995;Steinman, 1996), depth (Cantonati et al, 2009), type of substrate (Cazaubon et al, 1995;Eminson and Moss, 1980;Torrisi et al, 2006), hydrology (Falasco et al, 2016) and according to the presence of humic substances or metals (Morin et al, 2008). The high profile guild, by virtue of its position in contact with the water column, is probably the ecological guild under the influence of the greatest number of factors, including light , current intensity (Passy, 2007;Stenger-Kovács et al, 2013), predation (Steinman, 1996 and exposure to herbicides (Larras et al, 2014;Marcel et al, 2013;Rimet and Bouchez, 2011).…”

How does water scarcity affect spatial and temporal patterns of diatom community assemblages in Mediterranean streams?

“…Indeed, as far as the diatom indices have been conceived, the autecology of the taxa and the indicator species values for indices calculation are focused on the response to organic load and nutrient concentrations. Even though diatoms respond to the hydrological disturbance (Barthès et al., ; Falasco et al., 2016a; Sabater et al., ), its evaluation through community analysis still represent a challenge (Dallas, ; Falasco et al., 2016b). A better definition of the autecology of diatom species in Mediterranean streams could represent a key aspect for a proper quality classification of this stream typology.…”

“…We performed five sampling campaigns from April to September 2014, first in spring (April: 17/4/2014), with moderate flow, selected as a control, and the other four were conducted during water scarcity, every month from the end of June to the end of September (June: 30/6/2014; July: 22/7/2014; August: 28/8/2014; September: 24/9/2014). Water scarcity in the selected streams was mainly caused by rainfall scarcity and water uptakes (for further details see Falasco, Piano, & Bona, 2016b). Starting from these considerations and from field observations performed during water scarcity, we used the sampling date as a proxy of the temporal hydrological disturbance, since we observed a progressive and gradual lentification, fragmentation and isolation of stream stretches during summer.…”