THE ROLE OF BIOTURBATION IN SEDIMENT RESUSPENSION AND ITS INTERACTION WITH PHYSICAL SHEARING

Marine benthic fauna play an important role in governing sediment-water relationships, including resuspension of particle-borne contaminants. Constant burrowing and subsurface deposit-feeding tend to eject sediment into overlying water, break up the cohesive structure of silt-clay sediment, increase sediment-water content, and increase physical resuspension. Experimental evidence shows that resuspension of sediment is influenced by shear stress at the sediment-water interface and/or by the type, abundance and reworking time of infauna. Resuspension by biota was investigated by monitoring the turbidity of excurrent water of deposit-feeding species. The interaction between biota and physical shear in sediment resuspension was measured using an annular flume and a flume-calibrated Particle Entrainment Simulator. Sediment resuspension, in the absence of physical shear, was caused by Yoldia, Macoma, and Pectinaria during the disposal of pseudofeces (20 mg/min per individual Yoldia at 20-degrees-C. The presence of motile deposit-feeders also destabilized cohesive sediment and thus increased physical resuspension. The bivalve Nucula at least doubled physical resuspension at shear values above 2 dyne/cm2. Infaunal activities such as feeding, locomotion and habitat development resulted in direct resuspension and modified 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 of currents, depth and wave height and the biological terms vary with species, abundance and activity rates (temperature).