Macroinvertebrate community responses to river impoundment at multiple spatial scales

Hendrik J Krajenbrink,Mike Acreman,Michael J Dunbar,David M Hannah,Cédric L.R Laizé,Paul J Wood

doi:10.1016/j.scitotenv.2018.09.264

Abstract

River impoundment by the construction of dams potentially modifies a wide range of abiotic and biotic factors in lotic ecosystems and is considered one of the most significant anthropogenic impacts on rivers globally. The past two decades have witnessed a growing body of research centred on quantifying the effects of river impoundment, with a focus on mitigating and managing the effects of individual large dams. This study presents a novel multi-scale comparison of paired downstream and control sites associated with multiple water supply reservoirs (n = 80) using a spatially extensive multi-year dataset. Macroinvertebrate community structure and indices were analysed in direct association with spatial (e.g. region) and temporal variables (e.g. season) to identify consistent patterns in ecological responses to impoundment. Macroinvertebrate communities at monitoring sites downstream of water supply reservoirs differed significantly from those at control sites at larger spatial scales, both in terms of community structure and taxa richness. The effect was most significant at the regional scale, while biogeographical factors appeared to be important drivers of community differences at the national scale. Water supply reservoirs dampened natural seasonal patterns in community structure at sites downstream of impoundments. Generally, taxonomic richness was higher and %EPT richness lower at downstream sites. Biomonitoring indices used for river management purposes were able to detect community differences, demonstrating their sensitivity to river regulation activities. The results presented improve our understanding of the spatially extensive and long-term effects of water supply reservoirs on instream communities and provide a basis for the future implementation of mitigation measures on impounded rivers and heavily modified waterbodies.

Highlights

Streams and rivers are among the world's most threatened ecosystems (Malmqvist and Rundle, 2002; Vörösmarty et al, 2010; WWF, 2016), mainly as a result of increased anthropogenic management and modification on a global scale (Nilsson et al, 2005)
This study presents a novel multi-scale comparison of paired downstream and control sites associated with multiple water supply reservoirs (n = 80) using a spatially extensive multi-year dataset
The results of this study clearly indicate significant differences in macroinvertebrate community structure between monitoring sites downstream of impounding water supply reservoirs and unregulated control sites

Summary

Introduction

Streams and rivers are among the world's most threatened ecosystems (Malmqvist and Rundle, 2002; Vörösmarty et al, 2010; WWF, 2016), mainly as a result of increased anthropogenic management and modification on a global scale (Nilsson et al, 2005). Benthic macroinvertebrate communities in particular have been intensively studied in relation to the effect of impoundment, with research examining community structure (Lessard and Hayes, 2003; Ladrera et al, 2015; Santos et al, 2017) and species diversity and richness (García de Jalón et al, 1994; Growns and Growns, 2001; Bredenhand and Samways, 2009) Both flow and thermal regime have been linked to changes to downstream macroinvertebrate communities (Petts, 1984; Martínez et al, 2013; White et al, 2017a). Since direct comparison of pre- and post-dam macroinvertebrate communities is often not possible, due to an absence of pre-impoundment baseline monitoring data (but see Armitage, 1978; Maynard and Lane, 2012), most studies have compared sites downstream of impoundments with control sites (i.e. sites assumed to represent unregulated conditions at the downstream sites e.g. Growns and Growns, 2001; Holt et al, 2015)

Methods

Results

Conclusion