Understanding marine microplastic dynamics using macroplastics as a proxy

Marine plastic litter has been a problem for decades. Charitable societies (e.g. Marine Conservation Society, Fidra etc) have been recruiting volunteers to help clean beaches and generate data as evidence to support the lobbying of governments to develop policies and implement relevant legislation to curb the problem. Whilst the volunteers were previously sourced from a relatively narrow demographic, the programme Blue Planet has brought the awareness of the abundance of plastic in the marine environment to a much wider general public and foster a desire to reduce the amount of plastic being used on a daily basis. Annually, ~13M tons of plastic enters the marine environment in a variety of forms, ranging from large plastic items to primary and secondary microplastics. The marine environment is inter-connected, therefore plastics are not only transported globally to regions where there is little anthropogenic input, but also sequestered in sediments and thus potentially released for decades to come. Much of the plastic litter arrives on beaches, and Scotland is no different to that. Although more organisations are looking at beach litter, understanding the transport and deposition of the material on beaches is limited as there have been few studies looking at this process. A recent study (Nelms et al. 2016) investigated litter around the UK and highlighted a deficiency of samples from the western and northern coastline of Scotland compared to other regions. Of the samples collected however, plastic dominated accounting for between 50-80% of the litter collected there. This PhD project will investigate whether hotspots of macroplastic deposition in the Scottish marine environment link to high levels of microplastics being found in the same location. The studentship will aim to predict areas of high macroplastic deposition initially using Turrell's (2018) hypothesis-driven model to predict how floating marine plastic is driven onto/moved off different beaches before refining the model to take into account other information e.g. derived from the Scottish Shelf model and other environmental variables. The model will be used to predict which beaches have high, and thus low, levels of macroplastics. Using targeted UAV surveys to collect aerial images, as well as information freely available through the SCRAPbook project, the model can be validated to see if the model predictions are correct and further refined as required. Beaches which have been predicted and validated to have high levels of macroplastic will be sampled for microplastics. The microplastics will be collected depending on the sediment type of the beach. In addition to the surface sediment being sampled and analysed, sediment will be collected at depths to elucidate if microplastics are being retained or are released back into the marine environment.