Marine Bottom Boundary Layer Sediment Flux Measurements of Fluidized Mud and Muck Using Vertical and Horizontal Sonde Arrays

ABSTRACT Fluid mud and fluidized muck measured during an environmental dredging project used passive sondes and a sampling protocol to quantify bottom boundary layer cohesive sediment flux density. Results describe the efficacy of dredging using movement of fluidized particulates as a surrogate estimation of muck movement reduction (MMR). Horizontal flux arrays passively capture moving particulate material. Near bottom fluid mud transport exceeds surface fluxes by more than 400 times. The results are important since they clearly demonstrate how the sondes can be used to passively capture and quantify high concentrations of fluid mud and muck within the marine bottom boundary layer. INTRODUCTION & BACKGROUND The purpose of this paper is to describe results a study and ongoing research related to the design, application and deployments of in-situ arrays of sondes. The passive collection devices and protocol for their use is intended to quantify the vertical structure of the horizontal mass flux density of fluid mud movement in the marine bottom boundary layer. During deployment periods of half a day, days, weeks and months the sondes integrate sampling of particulates passing through a cross-sectional area and thus perform continuous spatial-temporal measurement of moving particulate matter within the lutocline. The need for sampling water and sediment characteristics that integrate spatial and temporal time scales has been reported in Gibbs and Konwar (1983) and Bianchi (2007). It has been noted that cohesive sediment particles such as flocs and colloidal aggregates within the bottom boundary layer lutocline cannot be sampled with traditional sampling techniques. The measurement protocol used to address the above sampling requirements make use of arrays (vertical and horizontal) of sondes designed to directly measure mass flux density (g m day) of resuspended cohesive sediments in coastal water bodies. Using the passive sondes allows measurements to be made that avoid noisy calibration problems common to optical and acoustic backscatter sensors (Gartner, 2009) that are spatial point measurements. These instruments do not have flux conserving properties used to estimate mass transport of fine grain particulate matter in the bottom boundary layer. In general, the use of the sonde technique allows one to passively capture or trap flocs and colloidal aggregates that move within or near the bottom lutocline as the particulates pass thru the sonde's horizontal cross-sectional area opening. The sondes can be deployed in different horizontal directions. This deployment procedure allows the fluid mud particles to enter the sonde through its cross sectional opening. Thus, fluid mud fluxes in different flow directions are quantified as shown in previous studies and described in Rotkiske and Bostater (2015).