Stace Beaulieu (Postdoctoral Investigator, AOPE) and Roger Francois (Associate Scientist, MCG)
 
 

SYNOPSIS

Resuspension of the uppermost sediments in coastal systems impacts water clarity, nutrient cycling, and dispersion of metals and other anthropogenic contaminants. Specifically, resuspension of the "fluff" atop more consolidated sediments may have important implications for the cycling of organic matter and metals in coastal systems. This "fluff" may adsorb or release different metals at different rates than the more consolidated, underlying sediments. The effect of toxic metals (e.g. Cd, Ag, Pb, Cu) on environmental quality depends on whether these metals are rapidly bound and irreversibly removed to the underlying sediments. Resuspension of particulate organic matter comprising surficial floc might promote the remobilization of metals to the water column, increasing their residence time in coastal ecosystems and amplifying their deleterious effect.

As a first step towards addressing that important issue, we are interested in determining the potential impact of resuspension of "fluff" on the transport dynamics of organic matter and associated metals in Buzzards Bay. Our objectives for this project are (1) to measure directly, in situ, the shear stress(es) necessary for resuspension of organic matter and associated metals from the uppermost sediments at two sites in Buzzards Bay, (2) to contrast the organic matter and metal content of resuspended and consolidated sediment, and (3) to predict, using hydrographic time series, resuspension events for organic matter and metals from the uppermost sediments during summer in Buzzards Bay.

In order to study these processes in Buzzards Bay, we are using an instrument called Sea Carousel. Sea Carousel is a submersible, annular flume about 2 m across that encloses sediments with about 20 cm of overlying water. The lid of Sea Carousel is programmed to rotate at increments of increasing speed, causing the flow velocity of water within the flume to increase. Consequently, stress on the sea bed within the flume increases. The stress quickly becomes great enough to erode flocculent surface sediments, and, at higher stresses, underlying sediments are resuspended. Water samples, taken at increasing bed stresses, are drawn from ports on the side of the flume up to the deck of Asterias.

For this project we are collaborating with scientists from Franklin and Marshall College and the Southampton Oceanography Centre. Sea Carousel is operated by the Geological Survey of Canada.