Sediment-to-water fluxes of particulate material and microbes by resuspension and their contribution to the planktonic food web

Abstract

Resuspension of bottom sediments by waves, currents, and biota is a potentially important mechanism by which particulate materials are introduced into the water column. Fluxes of particulate materials between sediments and overlying water were determined in the laboratory Box cores of nearshore marine sediments were subjected to defined shear stresses in an annular flume. Sediment resuspension was detectable at shear velocities (U,) of 0.95 to 1.35 cm S-' in sediments ranging from fine to coarse sands. An average sediment subjected to shear velocities of 1.16 to 1.50 cm S-' contributed 346 to 2312 mg particulate C m-'h-', 43 to 266 m g particulate N m-' h-', and 3 5 X 10" to 2 X 10" bacteria m-' h-' These fluxes would increase the concentrations of those substances in a 10 m homogeneously-rnlxed water column by 37 to 246 pg particulate carbon I-', 4.6 to 28 3 pg particulate N 1-' h-', and 3.7 X 104 to 2.2 X 105bacteria I-' h-', and would double typical water column concentrations in the field within a few hours. Shear stresses applied to sediments in these simulations represent mild field resuspension conditions (on the order of 0.5 m amplitude waves in 20 m water depth). Intense winter storms, which are not uncommon, would likely increase flux estimates according to the depth of sediment fluidzation, and according to depth profiles of sedimentary physico-chemical parameters. Resuspension, in this study area, appears to play a greater role in relocating particulate than dissolved nutnents.