Vertical redistribution of pebbles by crayfish in mollisol catenas of central illinois
2004
Robertson, Kevin M. | Johnson, Donald L.
Soil mixing by organisms (bioturbation) has an important influence on the distribution of rock fragments in soils. In east-central Illinois, pebbles were observed on the surfaces of loessal catenas. We hypothesized that surface pebbles are brought to the surface from the underlying glacial drift by burrowing crayfish. We predicted that (i) the spatial distribution of surface pebbles on catenas reflects crayfish habitat, (ii) pebbles are at least as abundant in crayfish chimneys (surface mound structures) as in the surrounding topsoil, (iii) pebbles are no larger than the cross-sectional diameter of crayfish burrows, (iv) the distribution of pebbles with regard to size class and material type does not differ between chimneys and surface soil samples, and (v) the vertical distribution of pebbles in the soil will reflect vertical mixing rather than a concentration at the soil surface. To test these predictions, surface pebbles were compared among catena members and crayfish chimneys and soil cores were collected and analyzed for pebble content and characteristics at multiple sites. The vertical distribution of pebbles in the soil profile was also studied at one site, and results were largely consistent with the hypothesis. However, the vertical distribution of pebbles suggested that near-surface pebbles subside at a greater rate than they are vertically mixed by crayfish, presumably due to bioturbation by other soil organisms. The study underscores the need to consider the influence of biota in addition to physical factors in interpreting the typically complex pathways of pedogenesis.
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