Remobilization of fine-grained sediments under blue mussel plots

Abstract

This paper presents a study of the role of the hydrodynamics on sedimentologic processes under blue mussel aquaculture plots. During the period from July 10th to July 27th, 1999, an intensive experiment was carried out to acquire oceanographic and sedimentologic data at the blue mussel aquaculture site of Itapocoroy embayment, Penha County, SC. The experiment consisted on the mooring of a wave and current meter, fixed in a tripod with its sensors leveled at 1 m above the bottom. A sediment trap system was attached to the mooring. The sediment traps were replaced every day, and placed at 0.5, 1.0 and 1.5 m above the bottom. During the experiment, two periods of high wave action due to by the passage of frontal systems, reaching a significant maximum wave height of 0,25 m. The currents had no noticeable variation during the entire experiment, presenting an averaged velocity of 4.7 cm.s-1. The potential sedimentation rates from the sediment traps were highest during highest wave activity. A conceptual model of the sedimentology under the mussel culture based on the observations suggests that the suspended sediments enter in the embayment by advection, being filtered by organisms and settled as fecal pellets. Wave energy destroys the pellets and allows the desagregated sediment to be more effectively ressuspended, and transported by the currents away form the aquaculture sites.