However, where bioturbation is coupled to other soil movement processes such as rainwash, and/or where the biomixing depth function varies with depth and/or where the incorporation of other constituents such as organic matter also varies with depth, horizonisation is expected (e.
This depth is coincident with the trees' rooting depth, and mixing has led to homogenisation of the topsoil here, because surface sorting by rainwash is inhibited by persistent vegetation cover, and tree turnover is capable of exhuming a large range of particle sizes.
Humphreys GS, Mitchell PB (1983) A preliminary assessment of the role of bioturbation and rainwash on sandstone hillslopes in the Sydney Basin.
Biomixing may also develop an earthy fabric and, in conjunction with rainwash
, may also lead to the coarsening in textures at the near surface (Paton et al.
Firstly, the positioning, stability, and texture of the proteoid root mat mitigates the effectiveness of rainwash.
It is inferred from the evidence of stable binding mechanisms that the root mat protected the mineral soil from the action of rainsplash and rainwash, and trapped sediment washed into the leaf litter from upslope.
If the above hypothesis is correct, the presence of fabric Type 4 in association with maculae suggests that proteoid roots can reduce the effectiveness of rainwash and cause the re-incorporation of fine material deposited at the soil surface by bioturbation.
In addition to the winnowing effect of bioturbation and rainwash proposed by Humphreys and Mitchell (1983), proteoid root mats actively retain medium-to-coarse material.
The arguments for proteoid roots mitigating the effectiveness of rainwash and contributing to the development of texture contrast initially appear contradictory.
Although this lag material would remain susceptible to erosion by rainwash
, it is inferred that the presence of the coherent, persistent root mat establishes a physical limit to the depth of soil over which erosive processes operate.