Bioturbation

Abstract

Bioturbation is the biogenic transport of sediment particles and pore water which destroys sediment stratigraphy, alters chemical profiles, changes rates of chemical reactions and sediment-water exchange, and modifies sediment physical properties such as grain size, porosity, and permeability. It is a natural consequence of the adaptation of organisms to live, forage, and respire in sediments. In the narrowest sense, bioturbation refers to the displacement of particles by organisms living within sedimentary deposits, but the term is often used more generally to describe the effects of organisms on particle reworking, pore-water transport, and physical changes to sediment through the production of fecal pellets, burrows, and surface traces. Deposit feeding by benthic infauna is considered to be the most widespread and dominant mechanism of particle reworking, but foraging in sediment by larger organisms such as fish and marine mammals can result in significant particle and pore-water exchange within patches. The ventilation of burrows by infauna is considered to be the dominant mechanism of pore-water transport, termed bioirrigation. Rates of bioturbation are most often estimated by measuring the profiles of tracers, such as naturally occurring radionuclides, in the sediment and comparing these tracer profiles to a mathematical model that includes bioturbation as a transport mechanism. In these models, bioturbation is often assumed to operate in a manner analogous to diffusion and is quantified as a biodiffusion coefficient. Models that account for more realistic bioturbation mechanisms exist as well. Bioturbation has important effects on benthic communities. It redistributes organic matter which serves as food for benthic organisms, it enhances the exchange rate of nutrients and other solutes between sediment and overlying water, and it can act as an agent of sediment disturbance, altering benthic community structure.