The Effect of Marine Aquaculture on Fine Sediment Dynamics in Coastal Inlets

Abstract

The formation and deposition of large, fast-sinking aggregates by flocculation governs the distribution of fine particulate material within the coastal zone. Three major factors control the development of a flocculated suspension: (1) particle number or concentration, (2) particle adhesion efficiency or stickiness, and (3) particle break-up, most often due to an applied shear. The steady state equilibrium size distribution of a flocculated suspension reflects a dynamic balance between particle aggregation and disaggregation; changes to concentration, composition, or turbulence can hence affect the distribution of fine particulate material, both inorganic and organic. Owing to the close association of many surface-active contaminants with flocs, the aggregation dynamics of the particulate material will strongly influence their fate. The introduction of waste feed, faecal material, and their resulting degradation products from open cage aquaculture operations in the coastal zone will potentially increase both particle concentration and particle stickiness. As a result, the natural flocculation and depositional equilibrium of an inlet can shift towards increased deposition of fine-grained particulate material within flocs and the sequestering of contaminants within the sediment. Evidence for such a shift in fine-sediment dynamics and contaminant transport has been found in the Western Isles region of New Brunswick.