River reaches with impaired riparian tree cover and channel morphology have reduced thermal resilience

Abstract

This study evaluated the effects of riparian tree cover and channel morphology on the thermal regimes of 3 adjacent rivers in different years. Riparian tree cover was found to exert a strong modifying influence on stream temperature, with reduced mean maximum summer temperature at sites having greater tree cover. The effect of tree cover changed among years, such that greater cover was required to maintain a given water temperature regime in the warmer summer of 2013 than in 2014 or 2015. Water temperature was also related to mean depth in some years; shallower sites, typically associated with artificial channel widening, showed greater temperature extremes. These results suggest that the thermal resilience of modified streams can be improved by restoration of riparian tree cover and restored channel morphology. This finding is relevant to climate change proofing of temperate river channels, where cold‐water fauna are important elements of the biotic community.

River modification reduces climate resilience of brown trout (Salmo trutta) populations in Ireland

“…Cover type was estimated within the average bankfull width for 800 m upstream of each temperature logger, as per O'Briain et al. (). Each randomly generated point was classified according to user‐defined cover classes (bare, improved grassland/rough pasture, hard surface (urban), tall herb, tree, open water).…”

“…There is little evidence to indicate local adaptation to high temperatures among populations or species (Almodóvar, Nicola, Ayllón & Elvira, ; Elliott, ; McCullough, ), although there is limited support for potential adaptation among some populations (e.g., Jensen et al., ). Assessment and management of thermally vulnerable river catchments are therefore necessary to maintain suitable habitat conditions for salmonids and other cold‐water species (Clarke, ; Durance & Ormerod, ; O'Briain, Shephard & Coghlan, ; Tockner, Schiemer & Ward, ).…”

“…The Broadmeadow and Delvin catchments on the east coast of Ireland have been subject to ongoing investigations since 2013, exploring their ability to buffer thermal extremes (O'Briain et al., ). O'Briain et al.…”

“…O'Briain et al. () reported a strong relationship between physical river modification and observed stream temperatures exceeding the known thermal thresholds for cold‐water species, such as brown trout, during the summers of 2013–2015. Building on these findings, the present investigation explored the response of the fish community to these interacting stressors, that is, physical habitat degradation and high stream temperature, in the same study catchments.…”

“…The dual concepts of resistance and resilience can help inform research investigating the potential impacts of a changing climate and mitigation strategies to ameliorate negative effects on freshwater biota. The Broadmeadow and Delvin catchments on the east coast of Ireland have been subject to ongoing investigations since 2013, exploring their ability to buffer thermal extremes (O'Briain et al, 2017b). O'Briain et al (2017b) reported a strong relationship between physical river modification and observed stream temperatures exceeding the known thermal thresholds for cold-water species, such as brown trout, during the summers of 2013-2015.…”