The stability of seabed sediments in the embayments of North Rustico, Prince Edward island, Canada

Abstract

This paper describes a series of 15 Sea Carousel deployments made along the two estuaries of North Rustico, Prince Edward Island, Canada: The Hunter river estuary and the Wheatley river estuary. The study was part of a wider study on the environmental impact of coastal changes and aquaculture (Mytilus edulis) development in the region. The study site is situated on the dynamic north shore of PEI characterised by sandy barrier islands, inlets and beaches, and muddy lagoons. The lagoons are dominated by the sea grass Zostera marina in the muddy outer parts and by Ulva lactuca in the eutrophic inner parts. The thresholds for surface erosion of cohesive sediments (0.10 < ?crit,o < 0.75) derived from trends of suspended sediment concentration (C) increases with distance (d) into the estuary: ?crit,o = 0.50exp-0.26d (±0.05) Pa. Location in the estuary is the best predictor of bed stability. The next best predictor is surface sediment wet bulk density (BD) which takes the form: ?crit,o = 6.67E-4(?b) - 0.55 Pa. Erosion rates (E) can only be correlated (significantly) with excess bed shear stress (?ex) by incorporation of a time (depth) varying erosion threshold. A power function emerged of the form: E = Eo?exn (0.28 < n < 1.06). The exponent is within the range from laboratory experiments reported in the literature. The still water settling rates of eroded material are diagnostic of a wide range of sedimentation diameters varying from fine sand to medium silt. The deposition threshold (?d) was evaluated in Lab Carousel for RUS11 and RUS12 and yielded a mean value of 0.51 Pa. The exponential decay constant (k) for still water settling is strongly dependent on initial concentration and suggests a constant settling rate that fits with data from a wide variety of settings throughout Canada.

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Identifiers

ORCID for C.E.L. Thompson: orcid.org/0000-0003-1105-6838

ORCID for H. Kassem: orcid.org/0000-0002-5936-6037

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