An invertebrate-based index to characterize ecological responses to flow intermittence in rivers

Judy England,Michael J Dunbar,David Leeming,Romain Sarremejane,Richard Chadd,Rachel Stubbington,Christian G Westwood

doi:10.1127/fal/2019/1206

Abstract

Intermittent streams occur across global regions, and are increasingly recognized to support high bio-diversity and perform important ecological roles within catchments. New tools are needed to better characterize biotic responses to the full spectrum of environmental conditions that occur in these dynamic systems, because the biological indices developed to assess ecological responses to flow in perennial rivers may be inaccurate in intermittent streams. We present the Monitoring Intermittent Streams index (MIS-index), a new biological index that can be used to assess invertebrate responses to environmental changes spanning flowing, ponded and drying states. As well as fully aquatic taxa, the index includes semi-aquatic and terrestrial invertebrates from marginal habitats, which are collected during the standard surveys used by regulatory agencies to assess ecological quality. We explore how including these taxa within an index informs our understanding of aquatic–terrestrial invertebrate community responses to changing habitat composition, as intermittent streams transition from lotic to lentic then drier conditions. We explain the development of the MIS-index and explore its performance compared with other indices. We suggest index combinations that can be used to detect different aspects of ecological responses to variation in instream conditions, and highlight the advantages of including semi-aquatic and terrestrial taxa. We call for researchers to test the performance of the MIS-index across a wide range of intermittent stream types, to enable its development into an internationally applicable tool for the holistic assessment of ecological responses to changing hydrological conditions including drying.

Highlights

Intermittent streams are natural ecosystems that experience profound changes in instream conditions including the cessation of flow and, typically, the partial or complete loss of surface water
We present the development of a new invertebrate index, which incorporates lotic, lentic, semi-aquatic and terrestrial taxa to characterize ecological responses to habitat changes associated with flow intermittence: the Monitoring Intermittent Streams index (MIS-index)
We modelled the responses of taxa richness to intermittence (=F) in each MIS-group together as a multivariate response in one generalized linear mixed-effects models (GLMM), using the function MCMCglmm in the package MCMCglmm (Hadfield 2010)

Summary

Introduction

Intermittent streams are natural ecosystems that experience profound changes in instream conditions including (by definition) the cessation of flow and, typically, the partial or complete loss of surface water. Ecological responses to altered flow regimes can be pronounced if flow permanence shifts from perennial to intermittent or vice versa, and in intermittent streams, changes in the extent of dry phases cause profound shifts in community composition (Datry et al 2017). Community responses may be effectively summarized by indices that characterize ecological effects and inform setting of hydroecological objectives to mitigate anthropogenic and drought impacts and, where necessary, to restore natural flow regimes (Klaar et al 2014). The LIFE (Lotic-invertebrate Index for Flow Evaluation) index (Extence et al 1999), calculated using the flow preferences of aquatic invertebrate taxa, is used to assess ecological responses to changing flow regimes (Gosling 2012; Klaar et al 2014)

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Discussion

Conclusion