Burial and turbulent transport by bioturbation: a 27‐year experiment in southeast Australia

Abstract

In order to assess the net effect and relative importance of geomorphic processes at two natural woodland sites in southeast Australia, 100 small tiles were placed on the soil surface in 1979 and their movement was monitored over the course of nearly three decades. Rates of tile burial and other tile displacement were considerable but also markedly random, being largely inconsistent with expected patterns of displacement by orthodox creep and rainwash processes. This included substantial upslope displacement and burial depths that ranged from zero to 5 cm. We suggest that such turbulent transport in the topsoil has mostly been caused by the direct and indirect transfer of soil and clasts by animals and plants (i.e. bioturbation). In addition to direct evidence of biota interacting with tiles, the effectiveness of bioturbation at our sites has been well established and the overall tile burial rate of 0·25 to 0·4 mm yr −1 is comparable to rates of surface mounding. Patterns of tile movement are generally consistent with soils-geomorphic theory regarding the biomantle and bioturbation-driven stonelayer formation, and provide further evidence that soil transfer and slope movement, in many situations, are markedly random and complex processes.

Bioturbation on a south-east Australian hillslope: estimating contributions to soil flux

“…Perhaps the most challenging consideration in future studies on this topic will be the inclusion of subsurface mixing in flux formulations, particularly in relation to mechanisms such as the collapse and infilling of biovoids (Wilkinson et al, 2009) and the subtle but ubiquitous displacement of soil by root and trunk growth (Phillips and Marion, 2006). Subsurface soil transfer by Californian gophers reportedly demonstrates considerable independence from hillslope angle (Gabet, 2000;Seabloom et al, 2000), and evidence of random subsurface displacement by bioturbation has been found at Cattai, 85 km north of the study hillslope (Humphreys and Field, 1998;Richards and Humphreys, 2010). Suggested to have made errors in calculating pit volumes using the half an ellipsoid method (Mills, 1984;Norman et al, 1995), Gabet et al (2003) used corrected volumes.…”

Time-Of-Flight monitoring reveals higher sediment redistribution rates related to burrowing animals than previously assumed

“…Field experiments with, for example, rainfall simulators can unveil processes but cannot cover the time-dependant natural dynamics of sediment redistribution. For data samplings that used methods such as erosion pins or splash boards, the sites had to be revisited each time and the data were thus obtained only sporadically (Imeson and Kwaad, 1976;Hazelhoff et al, 1981;Richards and Humphreys, 2010). Similarly, estimations of the excavated sediment volume are currently limited to one-time measurements or studies conducted several months apart (Black and Montgomery, 1991;Hall et al, 1999;Yoo et al, 2005).…”

7.13 Processes, Transport, Deposition, and Landforms: Quantifying Creep

“…' In the first style of pit, reference pegs are inserted into the immobile rock beneath the mobile soil and a line of 10 cm metal rods is inserted into the soil profile, normal to slope, exposed on the side of the pit ( Figure 5(b)). Despite two publications in Nature (Young, 1960(Young, , 1963a, few studies have followed the lead of this challenge (e.g., Schumm, 1967;Finlayson, 1981;Clarke et al, 1999), including a modified approach (Richards and Humphreys, 2010) that yielded results no less equivocal. In both cases, the pit must then be filled in and the soils must be 'allowed' to erode by creep for some length of time.…”

“…Given the results (or lack thereof) from the two most recent studies (Clarke et al, 1999;Richards and Humphreys, 2010), few others have attempted to follow Andrew Young's inspirational lead. Given the results (or lack thereof) from the two most recent studies (Clarke et al, 1999;Richards and Humphreys, 2010), few others have attempted to follow Andrew Young's inspirational lead.…”