BIOTURBATION - A FACILITATOR OF CONTAMINANT TRANSPORT IN BED SEDIMENT

The biological activity of benthic organisms (=bioturbation) in bed sediments can be significantly more important than physicochemical processes in the movement of sediment particles and interstitial constituents within the sediment column and to the overlying water. Bioturbation‐driven transport processes may be several orders of magnitude more rapid than molecular‐driven processes for some constituents, i.e., particle reactive compounds like PCB, when considered on a chemical pore water concentration gradient basis. Benthic organisms affect particle redistribution and solute transport by burrowing, ingestion/excretion, tube‐building and biodeposition. In most benthic environments, whether freshwater, estuarine or marine, numbers of organisms and rates of sediment turnover are highest in the oxygenated zone above the redox boundary, generally the top 2–5 cm of the sediment column. However, a variety of organisms penetrate deeper into the sediment and may also be important in transport of both dissolved and particle reactive constituents. When considering capping of contaminated sediment in place or capping of contaminated dredge spoils, the effects of bioturbation on the mobility of the contaminants must first be considered before establishing engineering design criteria. Capping of contaminated bed sediments or dredge spoils can elevate the bioturbated zone above the contaminated bed sediment and thus potentially reduce the rate of contaminant transport by several orders of magnitude. Copyright © 1990 American Institute of Chemical Engineers (AIChE)