Modelling accumulation of marine plastics in the coastal zone; what are the dominant physical processes?

Combining Litter Observations with a Regional Ocean Model to Identify Sources and Sinks of Floating Debris in a Semi-enclosed Basin: The Adriatic Sea

“…Stagnation at a solid boundary signifies beaching (Lebreton et al, 2012;Mansui et al, 2015) and particles that encountered the open boundary are marked as having left the basin and are excluded from subsequent analyses. While these processes are undoubtedly important, the uncertainty associated with each parameter remains quite large (Critchell and Lambrechts, 2016). Furthermore, we did not use subgrid processes parametrization under 2 km because the parameters of subgrid processes are basically unknown at those scales and we would have added further uncertainty in the results (Griffa, 1996;Haza et al, 2012;Carlson et al, 2016).…”

“…Inclusion of a stochastic term complicates backwards particle tracking (see Section 4.2) and near-shore stochastic motion could cause a particle to erroneously "jump" onto, or off of, land (Carlson et al, 2010). Windage and degradation are not considered as the effects of both variables on the transport of AMD are still poorly understood (Yoon et al, 2010;Critchell and Lambrechts, 2016). As such, the results presented here are most applicable to buoyant AMD with minimal above-water surface area, such as fragments made of polyethylene and polypropylene, which indeed represent the two most abundant polymers found in surface waters worldwide, as well as in the Mediterranean Sea .…”

“…While progress has been made, most relevant studies either relied on observations of beached AMD (Yoon et al, 2010;Kako et al, 2011Kako et al, , 2014Neumann et al, 2014), made assumptions about the amount of AMD as well as its temporal and/or spatial distributions (Lebreton et al, 2012;Critchell et al, 2015;Mansui et al, 2015;Liubartseva et al, 2016), or used coarse resolution velocity data and/or idealized surface currents (Aliani and Molcard, 2003;Maximenko et al, 2012;van Sebille et al, 2012;Reisser et al, 2013;Isobe et al, 2014). Such studies have identified the physical processes relevant to the transport and accumulation of debris, however, the efficacy of models in aiding management efforts depends strongly on the assumptions applied in the particle tracking scheme (Critchell and Lambrechts, 2016) as well as the resolution and accuracy of the underlying velocity field (Putman and He, 2013). Beaching, for example, is a complex process that is not properly represented in most particle tracking models (Lebreton et al, 2012) as ocean model domains typically extend to some minimum depth and, therefore, do not resolve the shoreline.…”

“…Furthermore, even relatively highresolution regional models, like the one employed here, cannot resolve complex shoreline topography. Additionally, a resource manager coordinating cleanup efforts is not faced with the mean state, which is most commonly reported by modeling studies, but instead must respond to debris loads that can vary in space and time (Kako et al, 2010(Kako et al, , 2011 in response to numerous environmental (Critchell and Lambrechts, 2016) and human factors (Slavin et al, 2012;Munari et al, 2016).…”

“…Advancing the study and management of anthropogenic marine debris (AMD) requires accurate identification of source regions (Critchell and Lambrechts, 2016) and quantification of temporal variability of injection rates. Identifying sources and sinks of AMD can assist resource managers maximize the effectiveness of prevention and response efforts by providing scientific support to the implementation of public policies.…”