Upper Delaware Bay Microplastic Distribution in Relation to the Estuarine Turbidity Maximum Zone

Ian Johnson, United States and Jonathan Cohen, University of Delaware, School of Marine Science and Policy, Lewes, DE, United States
Microplastic pollution is an emerging pollutant of concern in the marine environment, with significant gaps in understanding concerning its transport and ultimately its ecological effects. We hypothesize that microplastic particles aggregate in the Estuarine Turbidity Maximum zone (ETM) of Delaware Bay. We tested this hypothesis in June 2019, sampling seven sites in the Delaware Bay ETM using a multi-net tucker trawl with 200-micron mesh to provide depth-stratified samples at each site. Samples were processed using wet hydrogen peroxide oxidation with density separation, followed by manual identification and typing. We found that microplastic concentration increased as we approached the ETM, with maximum surface concentrations of 15 pieces per cubic meter. The majority of all pieces classified were filaments. The majority of all pieces found were smaller than 1mm in diameter, however, at the two sites closest to the ETM pieces larger than 1mm comprised the majority of the plastic mass collected. We conclude that plastics are aggregating in the Delaware Bay ETM.