THE ROLE OF BIOTURBATION IN SEDIMENT RESUSPENSION AND ITS INTERACTIONWITH PHYSICAL SHEARING

Marine benthic fauna play an important role in governing sediment-wate r relationships, including resuspension of particle-borne contaminants . Constant burrowing and subsurface deposit-feeding tend to eject sedi ment into overlying water, break up the cohesive structure of silt-cla y sediment, increase sediment-water content, and increase physical res uspension. Experimental evidence shows that resuspension of sediment i s influenced by shear stress at the sediment-water interface and/or by the type, abundance and reworking time of infauna. Resuspension by bi ota was investigated by monitoring the turbidity of excurrent water of deposit-feeding species. The interaction between biota and physical s hear in sediment resuspension was measured using an annular flume and a flume-calibrated Particle Entrainment Simulator. Sediment resuspensi on, in the absence of physical shear, was caused by Yoldia, Macoma, an d Pectinaria during the disposal of pseudofeces (20 mg/min per individ ual Yoldia at 20-degrees-C. The presence of motile deposit-feeders als o destabilized cohesive sediment and thus increased physical resuspens ion. The bivalve Nucula at least doubled physical resuspension at shea r values above 2 dyne/cm2. Infaunal activities such as feeding, locomo tion and habitat development resulted in direct resuspension and modif ied physical resuspension. Total resuspension with respect to time (R( t)dt) was found to equal the sum of a physical resuspension term (R(p) ), a biological term (R(b)) and a physical-biological interaction term (R(pb)). While all terms are time-varying R(p) varies as a function o f currents, depth and wave height and the biological terms vary with s pecies, abundance and activity rates (temperature).