Assessing stream restoration and the influence of scale, variable choice, and comparison sites

Abstract

Assessing stream restoration remains an ongoing challenge. Conclusions about the effectiveness of stream restoration efforts vary throughout the literature. This uncertainty is likely due, in part, to the spectrum of scales at which restorations have been assessed, the different variables used for assessment, and the varying types of sites used for comparisons. Mitigating such uncertainty with stream restoration assessment requires perspectives that consider multiple sites, variables, and scales using approaches that are transferable and comparable. From 2004 to 2018, surveys of stream habitat and fish at 44 restored and unrestored sites were conducted in two adjacent watersheds in southwestern Wisconsin, USA. Using non-parametric randomization tests, means of 42 variables were compared between (1) watershed vs. watershed sites; (2) all restored sites vs. all unrestored sites, (3) restored sites vs. pre-treatment surveys, (4) restored sites vs. unrestored control sites, and (5) pre-treatment surveys vs. unrestored control sites. When applicable, these comparisons were also made at nested scales ranging from all sites in both watersheds to only contiguous sites with common survey periods. Comparing sites between the two watersheds revealed natural variability between watersheds with similar geology and land-use practices, though unexpectedly more differences were found between surveys of restored sites from the two watersheds than between unrestored sites. The most differences between surveys of restored and unrestored sites were observed at larger scales of consideration, but within a given watershed. Although relatively few variables differed between pre-treatment surveys and control sites, there were marked differences when each type of unrestored sites was separately compared with restored sites. Habitat variable differences were more robust and consistent than fish community variables across all comparisons. Deviating from traditional multivariate approaches and independently comparing a broad spectrum of individual variable means at various, nested scales underscored the importance of context and variable choice when assessing stream restoration.

River channel changes through time and across space: Using three commonly available information sources to support river understanding and management in a national park

“…Gregory's research was a forerunner of contemporary integrated approaches to developing understanding of river functioning in order to underpin sustainable river management practices. Such approaches recognize that rivers respond to different factors that operate across many spatial and temporal scales (Downs et al, 2013; Polvi et al, 2020; Wright, 2021) and so provide platforms for exploring forms and processes across those scales to build understanding of river functioning (Brierley & Fryirs, 2005; Fryirs, 2015; Gurnell et al, 2016; Rinaldi et al, 2017). These factors are social as well as hydrological, geomorphological, biogeochemical and biological (Anderson et al, 2019; Dunham et al, 2018; Friberg et al, 2017).…”

‘Fluvial geomorphology and environmental design’: Restitution for damage, rehabilitation, restoration or rewilding?

“…Fish are more likely to benefit than benthic invertebrates or macrophytes (Haase et al, 2013), and so achieving Good Ecological Status by restoration measures cannot be assured. Wright (2021) outlines the methodological problems of assessments at a spectrum of restoration scales and site characteristics, together with post‐project appraisals focusing on the habitat variables, not the biological outcomes because of the hasty completion and short duration of such studies. Deeper methodological questions, of direct relevance to ecogeomorphology: ‘What are we monitoring and why?’, were raised by Brierley et al (2010) and taken up by Naura et al (2011).…”

A Q‐method survey of stream restoration practitioners in the Driftless Area, USA

“…Others preserve or add woody vegetation in hopes of offering habitat structure and forage for terrestrial biota, providing allochthonous inputs of carbon and nutrients to stream ecosystems, and creating shade that may buffer streams from climate change‐induced temperature increases (Cross, Bozek, & Mitro, 2013; Fisher, Bozek, Vokoun, & Jacobson, 2012). These unresolved questions and differences of perspective have prompted ongoing debate about best practices and about what metrics should be used to assess the success of aquatic restoration projects (Bernhardt & Palmer, 2011; Palmer et al, 2005; Wright, 2021). Moreover, the perspectives and values of managers themselves often receive much less research attention than scientific debates and public stakeholder perspectives, with some exceptions (Druschke & Hychka, 2015; Hychka & Druschke, 2017; Nost et al, 2019; Primack, Sher, Maas, & Adams, 2021).…”

“…Though stream restoration has become relatively common, there is an ongoing debate about what constitutes “success” in restored systems and whether success should incorporate both scientific and stakeholder‐defined endpoints (Nost, Robertson, & Lave, 2019; Palmer et al, 2005; Shields, Cooper Jr, Knight, & Moore, 2003), as well as the acceptability of various stream restoration approaches and techniques (Lave, 2012). For instance, while academic research has taken a conceptual turn from reliance on hard‐engineered solutions toward more “natural,” process‐based designs (Johnson et al, 2020; Palmer et al, 2005), in practice, hard‐engineered structures are still widely employed, including rock riprap, artificial overhead cover, and engineered flow structures (Belby, Spigel, & Fitzpatrick, 2019; Wright, 2021), largely because of a focus on bank stabilization and habitat enhancement due to residential, recreational, and economic concerns (Bond & Lake, 2003; Wohl, Lane, & Wilcox, 2015). Further debate centers on riparian vegetation (Lyons, Thimble, & Paine, 2000), with some projects removing riparian woody vegetation to establish grasses in an attempt to narrow and deepen channels while providing better accessibility for fly angling (Hunt, 1993).…”

“…Stream restoration has grown into a global phenomenon, with the US hosting a multi‐billion‐dollar industry (Palmer et al, 2005; Wright, 2021). Though stream restoration has become relatively common, there is an ongoing debate about what constitutes “success” in restored systems and whether success should incorporate both scientific and stakeholder‐defined endpoints (Nost, Robertson, & Lave, 2019; Palmer et al, 2005; Shields, Cooper Jr, Knight, & Moore, 2003), as well as the acceptability of various stream restoration approaches and techniques (Lave, 2012).…”