Effects of Cyanobacterial Soil Crusts on Surface Roughness and Splash Erosion

Joanna E Bullard,Helene Aubault,Craig Strong,Annie Ockelford

doi:10.1029/2018jg004726

Abstract

AbstractSoil surface roughness (SSR) modifies interactions and feedback processes between terrestrial and atmospheric systems driven by both the abiotic and biotic components of soils. This paper compares SSR response to a low‐intensity multiday rainfall event for soils with and without early successional stage cyanobacteria‐dominated biological soil crusts (CBCs). A rainfall simulator was used to apply 2, 5, and 2 mm of rain separated by a 24‐hr period over 3 days at an intensity of 60 mm/hr. Changes in SSR were quantified using geostatistically derived indicators calculated from semivariogram analysis of high‐resolution laser scans. The CBCs were stronger and splash erosion substantially less than from the physical soil crusts. Prior to rainfall treatment, soils with CBCs had greater SSR than those without. The rainfall treatments caused the physical crusted soils to increase SSR and spatial patterning due to the translocation of particles, soil loss, and the development of raindrop impact craters. Rainfall caused swelling of cyanobacterial filaments but only a slight increase in SSR, and raindrop impact cratering and splash loss were low on the soils with CBCs. There is no relationship between random roughness and splash erosion, but an increase in splash loss was associated with an increase in topographic roughness and small‐scale spatial patterning. A comparison of this study with other research indicates that for rainfall events up to 100 mm, the effectiveness of CBCs in reducing soil loss is >80% regardless of the rainfall amount and intensity, which highlights their importance for landscape stabilization.

Highlights

Soil surface microtopography plays an important role in modifying interactions and feedback processes between terrestrial and atmospheric systems at a range of scales (Cammeraat, 2002; Martin et al, 2008; Rodríguez-Caballero et al, 2012; Smith, 2014)
The rainfall-drying sequence led to a successive increase in physical crust strength for both soils but the crust was stronger for soil APHYS, which has a higher clay and silt content, than for sand-rich BPHYS (Table 1)
This study examined the response of soil surface roughness to rainfall and differs from previous research in a number of ways

Summary

Introduction

Soil surface microtopography plays an important role in modifying interactions and feedback processes between terrestrial and atmospheric systems at a range of scales (Cammeraat, 2002; Martin et al, 2008; Rodríguez-Caballero et al, 2012; Smith, 2014). SSR at small scales is highly dynamic in response to raindrop impact as the soil structural units are broken down from macro-aggregates (>250 μm) to micro-aggregates (20-250 μm) to primary soil particles (Emerson and Greenland, 1990; Le Bissonais, 1996a, 1996b, 2005). This breakdown of structural units often results in the formation of physical soil crusts comprising a thin surface layer a few millimetres thick that is more dense and with a lower porosity than the underlying soil (Assouline, 2004). Surface sealing and ponding during physical crust formation typically reduces SSR (e.g. Croft et al, 2013; Vermang et al.2013), on fine soils under low rainfall the creation of raindrop impact craters may cause an increase in surface roughness (Bullard et al, 2018)

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