A comparison of biotic groups as dry-phase indicators of ecological quality in intermittent rivers and ephemeral streams

Rachel Stubbington,Amael Paillex,Judy England,Amélie Barthès,Agnès Bouchez,Frédéric Rimet,María Mar Sánchez-Montoya,Christian G Westwood,Thibault Datry

doi:10.1016/j.ecolind.2018.09.061

Abstract

Intermittent rivers and ephemeral streams (IRES) are dynamic ecosystems that shift between aquatic and terrestrial states. IRES are widespread, abundant and increasing in extent, but developing biomonitoring programmes to determine their ecological quality is challenging. To date, quality assessments have focused on the aquatic organisms present during wet phases, whereas dry-phase communities remain poorly characterized. We examined multiple biotic groups present in dry IRES channels, to compare assemblages at sites impacted and unimpacted by human activity and to evaluate the potential of each group as an ecological quality indicator. We explored existing, unpublished data for three biotic groups: an aquatic microflora (diatoms), an aquatic fauna (the invertebrate ‘seedbank’), and a mixed flora (aquatic and terrestrial plants); notably, we did not source data for terrestrial assemblages with high potential to act as indicators. Diatom and plant assemblage composition differed between impacted and unimpacted sites, and the latter assemblages were more diverse and included more indicator taxa. Invertebrate seedbank taxa richness was higher at unimpacted sites but compositional differences were not detected, probably due to the coarse taxonomic resolution to which abundant taxa were identified. Performance of standard indices of ecological quality was variable, but differences were identified between impacted and unimpacted conditions for all biotic groups. Our results can inform the enhancement of biomonitoring programmes designed to characterize IRES ecological quality in relation to legislative targets. We highlight the need to integrate wet- and dry-phase survey data in holistic quality assessments. Although we suggest diatoms, aquatic plants and the aquatic invertebrate seedbank as having the potential to inform assessment of dry-phase ecological quality, we highlight the need for research to further characterize these aquatic groups and, crucially, to explore terrestrial assemblages with high potential to act as dry-phase quality indicators.

Highlights

Intermittent rivers and ephemeral streams (IRES) are defined by freshwater ecologists as lotic ecosystems in which water sometimes stop flowing, and many systems experience partial or complete loss of surface water (Datry et al, 2017a)
We evaluated the potential of multiple biotic groups present in dry IRES channels to act as indicators of ecological quality, potentially of the quality of an IRES in general and/or of dry phases in particular
Assemblage composition differed among quality categories (ANOSIM, global R = 0.47, P = 0.007), with non-metric multi-dimensional scaling (NMDS) showing dispersed high-status samples and a lower-status cluster (Fig. 1)

Summary

Introduction

Intermittent rivers and ephemeral streams (IRES) are defined by freshwater ecologists as lotic ecosystems in which water sometimes stop flowing, and many systems experience partial or complete loss of surface water (Datry et al, 2017a). IRES are aquatic ecosystems that sometimes lose all flowing surface water, but are transition zones in which aquatic and terrestrial habitats can occur both successively and simultaneously (Datry et al, 2016). Ecological Indicators 97 (2019) 165–174 et al, 2017) These coupled aquatic-terrestrial ecosystems can dominate dendritic networks in drylands, are common in temperate regions, and are increasing in global extent in response to water resource demands, land use change and climatic drivers (Datry et al, 2017a; Stubbington et al, 2017)

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