oceanographyand limnology, bioturbation is the displacement and mixing of sedimentparticles by benthic fauna (animals)or flora (plants). The mediators of bioturbation are typically annelidworms (e.g. polychaetes, oligochaetes), bivalves(e.g. mussels, clams), gastropods, holothurians, or any other infaunal or epifaunal organisms. Faunal activities, such as burrowing, ingestion and defecation of sediment grains, construction and maintenance of galleries, and infilling of abandoned dwellings, displace sediment grains and mix the sediment matrix. The sediment-water interfaceincreases in area as a result of bioturbation, affecting chemical fluxes and thus exchange between the sediment and water column. Some organisms may further enhance chemical exchange by flushing their burrows with the overlying waters, a process termed bioirrigation. Benthic flora can affect sediments in a manner analogous to burrow construction and flushing by establishing root structures. Bioturbation is a diagenetic process and acts to alter the physical structure, as well as the chemical nature of the sediment.
soil science, bioturbation is the physical rearrangement of the soil profileby soil life. Plants and animals exploit the solumfor food, and shelter and, in the process, disturb the fabric of the soil and the underlying parent material[ Paton, T. R., Humphreys, G. S., and Mitchell, P. B., 1995, Soils: A New Global View: London, UCL Press Limited.] [ Shaler, N. S., 1891, The origin and nature of soils, in Powell, J. W., ed., USGS 12th Annual report 1890-1891: Washington, D.C., Government Printing Office, p. 213-45..] . Burrowing animals and insects, and plant root systems create passageways for air and water movement, changing soil morphology. A passageway created by an animal that becomes backfilled with soil is known as a krotovina. Invertebrates that burrow and mound soil tend to produce a biomantle topsoil, and as such are primary agents of horizonization [ Paton, T. R., Humphreys, G. S., and Mitchell, P. B., 1995, Soils: A New Global View: London, UCL Press Limited.] [ Shaler, N. S., 1891, The origin and nature of soils, in Powell, J. W., ed., USGS 12th Annual report 1890-1891: Washington, D.C., Government Printing Office, p. 213-45..] [Darwin, C., 1881, The formation of vegetable mould through the action of worms, with observations on their habits: London, John Murray.] [ Wilkinson, M. T., and Humphreys, G. S., 2005, Exploring pedogenesis via nuclide-based soil production rates and OSL-based bioturbation rates: Australian Journal of Soil Research, v. 43, p.767-779.] [http://www.uky.edu/AS/Geography/People/Faculty/Wilkinson/2005-WilkinsonHumphreysPedogenesisAJSR.pdf] . Uprooted trees break up bedrock, transport soil downslope, increase the heterogeneity of soil respirationrates, and disrupt soil horizonation. [ Gabet, Reichman, and Seabloom. 2003. The effects of bioturbation on soil processes and hillslope evolution. Annual Review of Earth and Planetary Sciences 31:249-273.] Bioturbation was initially unrecognized as a pedogenic force. The term didn't exist before 1952, when bioturbation was coined to aid in ichnological assessments. Bioturbation appeared in the soil and geomorphic literature in the early 1980s [ Humphreys, G. S., and Mitchell, P. B., 1983, A preliminary assessment of the role of bioturbation and rainwash on sandstone hillslopes in the Sydney Basin, in Australian and New Zealand Geomorphology Group, p. 66-80.] , and remains a key element of the pedogenic lexicon. Bioturbation is central to the biomantle concept formulated in 1990. The biomantle is the upper part of soil produced largely by biota, dominantly by bioturbation. Biomantles are one-layered when formed in fine fraction materials, and two-layered when formed in mixed fine-and-coarse materials. Bioturbation by burrowing animals results in soil landscapes that are both polygenetic and polytemporal.
Mathematical models are often used to describe sediment biogeochemistry. Commonly, these models take the form of ordinary differential equationsor partial differential equationsin which bioturbation appears as a diffusive term. A diffusive description is often adopted to avoid quantifying the plethora of mixing modes resulting from faunal activities. The diffusion coefficient describing the intensity of bioturbation is usually determined by fitting mathematical models to vertical distributions of natural radioactive tracers, radioisotopesresulting from nuclear weapontesting, or introduced particles, such as glass beads tagged with radionuclides.
Bioturbation's importance for soil processes and
geomorphologywas ﬁrst realised by Charles Darwin, who devoted his last scientiﬁc book to the subject ("The Formation of Vegetable Mould through the Action of Worms", 1881). Modern research has provided further insight into the evolutionaryand ecologicalrole of bioturbation. [ Meysman, Middelburg, and Heip. 2006. Bioturbation: a fresh look at Darwin’s last idea. TRENDS in Ecology and Evolution, doi:10.1016/j.tree.2006.08.002.] In modern ecological theory, bioturbation is recognised as an archetypal example of ‘ecosystem engineering’, modifying geochemical gradients, redistributing food resources, viruses, bacteria, resting stages and eggs. From an evolutionary perspective, recent investigations provide evidence that bioturbation had a key role in the evolution of metazoanlife at the end of the PrecambrianEra. [http://www.nioo.knaw.nl/ppages/jmiddelburg/downloads/1/Meysman_tree.pdf]
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