Abstract
Abstract. With knowledge of typical hydrodynamic behavior of waste plastic material, models predicting the dispersal of benthic plastics from land sources within the ocean are possible. Here we investigated the hydrodynamic behavior (density, settling velocity and resuspension characteristics) of non-buoyant preproduction plastic pellets in the laboratory. From these results we used the MOHID modelling system to predict what would be the likely transport and deposition pathways of such material in the Nazaré Canyon (Portugal) during the spring/summer months of 2009 and the autumn/winter months of 2011. Model outputs indicated that non-buoyant plastic pellets would likely be transported up and down canyon as a function of tidal forces, with only a minor net down canyon movement resulting from tidal action. The model indicated that transport down canyon was likely greater during the autumn/winter, primarily as a result of occasional mass transport events related to storm activity and internal wave action. Transport rates within the canyon were not predicted to be regular throughout the canyon system, with stretches of the upper canyon acting more as locations of pellet deposition than conduits of pellet transport. Topography and the depths of internal wave action are hypothesized to contribute to this lack of homogeneity in predicted transport.
Highlights
Marine microplastic pollution in the forms of preproduction pellets, fragments, filaments, films and foams originates from direct spillage and breakdown of plastic debris (Moore et al, 2011) and synthetic materials with densities ranging from∼ 0.9–1.4 g mL−1 (Morét-Ferguson et al, 2010; Andrady, 2011)
Bed load transport commenced at shear stresses of 0.014 N m−2 and approximately 50 % of pellets were in bed load transport at ∼ 0.025 N m−2. 75 % of pellets were in suspension at shear stresses of ∼ 0.14 N m−2 and pellets were re-deposited at shear stresses of ∼ 0.087 N m−2
Integrating over the entire 200 kmlong canyon system (Tyler et al, 2009), and assuming relatively constant hydrodynamic conditions, the results suggest benthic microplastic transport from the canyon head to the abyssal plain would take place on the centennial or longer scale, if at all
Summary
Marine microplastic pollution in the forms of preproduction pellets, fragments, filaments, films and foams originates from direct spillage and breakdown of plastic debris (Moore et al, 2011) and synthetic materials with densities ranging from∼ 0.9–1.4 g mL−1 (Morét-Ferguson et al, 2010; Andrady, 2011). Marine microplastic pollution in the forms of preproduction pellets, fragments, filaments, films and foams originates from direct spillage and breakdown of plastic debris (Moore et al, 2011) and synthetic materials with densities ranging from. Data on sub-surface microplastic abundance and distribution within the marine environment is limited in comparison to data on neustonic microplastics, due to the inefficiency of benthic and pelagic sampling in collecting such small material in conjunction with the remoteness and size of the benthic and pelagic habitat which may be affected. The need for a better means of estimating sub-surface microplastic transport is growing as plastic production levels increase (PlasticsEurope, 2010) and plastic debris accumulation increases worldwide (Barnes, 2009; Wright et al, 2013). Models may help identify and predict regions where ecological communities and fishery-dependent coastal societies are more vulnerable to the potential consequences of plastic pollution, such as associated toxicity to marine organisms and a decline of marine ecological services (Derraik, 2002; Lithner et al, 2009; Lithner et al, 2011)
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