Signal crayfish burrowing, bank retreat and sediment supply to rivers: A biophysical sediment budget

Abstract

Burrowing into riverbanks by animals transfers sediment directly into river channels and has been hypothesised to accelerate bank erosion and promote mass failure. A field monitoring study on two UK rivers invaded by signal crayfish (Pacifastacus leniusculus) assessed the impact of burrowing on bank erosion processes. Erosion pins were installed in 17 riverbanks across a gradient of crayfish burrow densities and monitored for 22 months. Bank retreat increased significantly with crayfish burrow density. At the bank scale (<6 m river length), high crayfish burrow densities were associated with accelerated bank retreat of up to 253% and more than a doubling of the area of bank collapse compared with banks without burrows. Direct sediment supply by burrowing activity contributed 0.2% and 0.6% of total sediment at the reach (1.1 km) and local bank (<6 m) scales. However, accelerated bank retreat caused by burrows contributed 12.2% and 29.8% of the total sediment supply at the reach and bank scales. Together, burrowing and the associated acceleration of retreat and collapse supplied an additional 25.4 t km−1 a−1 of floodplain sediments at one site, demonstrating the substantial impact that signal crayfish can have on fine sediment supply. For the first time, an empirical relation linking animal burrow characteristics to riverbank retreat is presented. The study adds to a small number of sediment budget studies that compare sediment fluxes driven by biotic and abiotic energy but is unique in isolating and measuring the substantial interactive effect of the acceleration of abiotic bank erosion facilitated by biotic activity. Biotic energy expended through burrowing represents an energy surcharge to the river system that can augment sediment erosion by geophysical mechanisms.

Invertebrate zoogeomorphology: A review and conceptual framework for rivers

“…Bioturbation and bioerosion (Box 1i and ii) redistribute sediment, changing both the physical structure of substrates and the chemical and biological processes occurring within (Gautreau et al, 2020; Mermillod‐Blondin, 2011). Bioerosion (Box 1i) is exhibited by taxa which burrow into rock or consolidated bed and bank sediment (Sanders et al, 2021; Savrda, 2019). Bioturbation (Box 1ii) is the most researched biogeomorphic effect in rivers (Albertson & Allen, 2015; Statzner, 2012) and is a product of several mechanisms (Figure 1).…”

“…Sanders et al (2021) provide the first long term (22‐month) empirical field evidence of a relationship between burrows and accelerated bank retreat and collapse. By destabilizing river banks, signal crayfish may supply more than 49 times as much sediment to river systems than burrowing alone, with accelerated retreat supplying 25.4 t km a −1 of additional sediment to a UK lowland river, contributing 12% of total sediment supply from riverbanks at the reach scale (Sanders et al, 2021). However, the mechanisms underpinning these changes outlined in Harvey et al (2019) are not yet understood, and are thus an important avenue of future research.…”

“…Freshwater invertebrates are also functionally diverse, exhibiting behaviors that facilitate large zoogeomorphic effects. For example, many invertebrate taxa erode sediment by burrowing (Faller et al, 2016; Rice et al, 2016; Sanders et al, 2021), while others consolidate sediment by building stabilizing structures (Albertson et al, 2019; Johnson et al, 2009). Consequently, invertebrates can have a diverse array of zoogeomorphic effects, mediated in part by their behavior.…”

Interaction Between Animal Burrowing and Loess Cave Formation in the Chinese Loess Plateau

“…Many areas in the CLP have a large population of subterranean rodents (Su et al, 2013;Sui et al, 2014;Zhang et al, 2021), because of the habitable grassland environment (Yu et al, 2017) and unlimited burrowing potential of loess (Krasnov et al, 1997). This burrowing activity has both direct and indirect impacts on geomorphic processes (Hall et al, 1999;Hall and Lamont, 2003;Escapa et al, 2007;Germain et al, 2021;Sanders et al, 2021). The burrowing process may directly cause soil displacement (Black and Montgomery, 1991) and alter the slope micromorphology (Zhao et al, 2021) as well as soil compactness (Rogasik et al, 2014).…”

Why so skeptical? The role of animals in fluvial geomorphology

“…Indeed, a large body of ecological research documents burrowing behavior in many species (Hobbs, 1981; Horwitz & Richardson, 1986), to the extent that Berrill and Chenoweth (1982) suggest that some crayfish burrow as a matter of course and all species will burrow when they need to, for example to establish a moist shelter or to find cover. Recent work has emphasized the importance of burrowing animals, including crayfish for river bank stability, bank erosion and sediment delivery to rivers (Harvey et al, 2019; Sanders et al, 2021). This example highlights the fact that we have only investigated the tip of the iceberg when it comes to identifying zoogeomorphic species, which are more common than is generally appreciated.…”