Determining the depth and rate of soil movement down the soil profile using an environmental tracer: a hillslope scale assessment

G. R. Hancock; A. Gibson; I. P. Senanayake; Tristan Cox

doi:10.1071/SR23253

RESEARCH ARTICLE (Open Access)

Next Contents Vol 62(4)

Determining the depth and rate of soil movement down the soil profile using an environmental tracer: a hillslope scale assessment

G. R. Hancock

^A ^* , A. Gibson ^B , I. P. Senanayake ^A and Tristan Cox ^A

+ Author Affiliations

- Author Affiliations

^A School of Environmental and Life Sciences, Earth Science Building, The University of Newcastle, Callaghan, NSW 2308, Australia.

^B Faculty of Science and Engineering, Southern Cross University, Military Road, East Lismore, NSW 2480, Australia.

^* Correspondence to: Greg.Hancock@newcastle.edu.au

Handling Editor: Siobhan Staunton

Soil Research 62, SR23253 https://doi.org/10.1071/SR23253

Submitted: 21 December 2023 Accepted: 4 April 2024 Published: 13 May 2024

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Soil materials can be delivered to depth from both in situ and ex situ materials. Here, we examine a hillslope in an agricultural environment that has been used for cropping and cattle grazing for over 150 years and a parallel area where cattle have been excluded for approximately 20 years. The exclusion area is a shelterbelt and also provides ecological services.

Aims

To quantify the depth and rate of down profile soil movement using the environmental tracer ¹³⁷Cs at points along a hillslope profile.

Methods

¹³⁷Cs concentration is measured to bedrock at regular intervals both inside and outside a fenced of ecological services area pre-drought (2015) and post-drought (2021). In Australia. ¹³⁷Cs is the by-product of nuclear weapons use and testing from1945 to 1972. Therefore, this places an age constraint on any labelled soil.

Key results

Results show that soil materials can move down the soil profile to reach bedrock at decadal time scales. An important finding is that materials from the surface can reach depths of up to 80 cm near the hillslope crest and up to 2.2 m at the base of the hillslope.

Conclusions

This demonstrates a relatively rapid translocation of surface material.

Implications

The method provides the ability to quantify the rapid movement of soil components and demonstrates the potential for deep sequestration of soil organic carbon. The results demonstrate the potential for soil amendments and agrochemicals to be rapidly transported to depth. The findings suggest that cattle exclusion has no impact on the movement of soil materials down the profile over the 20-year exclusion period.

Keywords: ¹³⁷Cs, carbon sequestration, cattle grazing, ecological services, environmental tracer, exclusion area, pedogenesis, shelterbelts.

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