Associations between riparian plant morphological guilds and fluvial sediment dynamics along the regulated Colorado River in Grand Canyon

Abstract

Effects of riparian vegetation on fluvial sediment dynamics depend on morphological traits of the constituent species. Determining the effects of different morphological guilds on sedimentation rates, as influenced by multiple aspects of dam operations, can help identify viable strategies for streamflow and vegetation management to achieve riparian resource goals. Plants of increasing size and branching density or complexity have been found to have greater effects on sedimentation in free‐flowing systems; however, this relationship could differ in regulated rivers. We tested the hypothesis that plant guilds of increasing height and branching complexity would be positively associated with sedimentation rates on 23 sandbars deposited in zones of recirculating flow (eddies) along the Colorado River in Grand Canyon. We used an image‐based vegetation classification and digital elevation models from annual topographic surveys to track associations between six plant morphological guilds and topographic change over 5 years. Vegetation had significant associations with deposition after accounting for geomorphic setting, but the ordinal guild scale was not positively correlated with deposition magnitude. Instead, low‐statured rhizomatous and herbaceous guilds were particularly effective at capturing sediment in the separation zone of sandbars, whereas tall herbs and large shrubs were most effective at capturing sediment in reattachment zones. These nuanced interactions between geomorphic position and morphological guild may be a direct consequence of flow regulation through modifications to physical deposition and erosion processes. Flow regulation may also select for a narrow subset of morphological guilds, reducing the diversity of vegetation feedbacks on sedimentation and emphasizing geomorphic drivers.

Exploring the 4D scales of eco-geomorphic interactions along a river corridor using repeat UAV Laser Scanning (UAV-LS), multispectral imagery, and a functional traits framework

“…Guild location impacts the morphological response, with analysis of bars showing different responses downstream and also laterally based on the traits of the dominant species in these directions (Hortobágyi et al, 2018). This is supported by Butterfield et al (2020) who when examining changes in multi-annual elevation found that guilds at different locations, experiencing different hydraulic conditions, had differing impacts, but also that guilds could not explain all the variation in morphological response. It was found that differing canopy https://doi.org/10.5194/esurf-2021-102 Preprint.…”

“…For fluvial research, multispectral imagery can be used to determine species using supervised and unsupervised classifications with good accuracy (Butterfield et al, 2020). Outside of fluvial research there is an increasing awareness of the potential of remote sensing methods to help drive the scalability of functional traits, especially in relation to physical traits such as plant height, leaf area index, phenology, and biomass (Abelleira Martínez et al, 2016;Aguirre-Gutiérrez et al, 2021), yet considerable limitations remain due to the uncertainty in relating spectral and physical properties to functional traits (Houborg et al, 2015).…”

“…Traits-based classifications, developed and used within ecology, offer a scalable and transferable approach which can be applicable to the fluvial domain (Diehl et al, 2017). They have been shown to be useful for modelling topographic response to changing vegetation, sediment, and flow conditions (Diehl et al, 2018;Butterfield et al, 2020). However, challenges remain in broad application of this approach, with the characterisation of vegetation in the highly detailed manner required to extract traits metrics being challenging over larger (e.g.…”

Hydrologic and geomorphic effects on riparian plant species occurrence and encroachment: Remote sensing of 360 km of the Colorado River in Grand Canyon

“…Expansion and other responses of riparian vegetation to changes in river flow associated with river regulation can differ by species, growth form, plant physiologyand native (invasive) status and can be affected by feedbacks with river sediment (Butterfield et al, 2020;Dean & Topping, 2019;Diehl, Merritt, et al, 2017;Manners et al, 2014). Moreover, river channels and riparian areas comprise a range of geomorphic landforms such as sandbars, gravel bars, talus slopes and tributary debris fans.…”

A Morphodynamic Model to Evaluate Long‐Term Sandbar Rebuilding Using Controlled Floods in the Grand Canyon

“…While bedrock and coarse sediment such as boulders form the rigid channel boundary, fine sediments comprise a dynamic and transient part of the river corridor (e.g., Skalak & Pizzuto, 2010). Fine sediments provide substrate for riparian vegetation, morphological complexity for the aquatic ecosystem, protection of archeological resources, and important recreational areas for visitors (Butterfield et al., 2020; East et al., 2017; Grams et al., 2010; Kaplinski et al., 2005; Korman et al., 2004; Meshkova & Carling, 2012). In canyon rivers where flow is strongly affected by bedrock or relatively immobile talus, flow hydraulics are often dictated by these fixed obstructions (Alvarez et al., 2016; Rennie et al., 2018; Venditti et al., 2014; Wright & Kaplinski, 2011).…”