Identification of tidal trapping of microplastics in a temperate salt marsh system using sea surface microlayer sampling

Jessica L Stead,Charlie E L Thompson,Andrea E Russell,Malcolm D Hudson,Katsiaryna Pabortsava,Andrew B Cundy,Ian D Williams

doi:10.1038/s41598-020-70306-5

Jessica L Stead, Charlie E L Thompson + Show 5 more

Open Access

https://doi.org/10.1038/s41598-020-70306-5

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Abstract

Microplastics are contaminants of increasing global environmental concern. Estuaries are a major transport pathway for land-derived plastics to the open ocean but are relatively understudied compared to coastal and open marine environments. The role of the “estuarine filter”, by which the supply of sediments and contaminants to the sea is moderated by processes including vegetative trapping and particle flocculation, remains poorly defined for microplastics land to sea transfer. Here, we focus on the sea surface microlayer (SML) as a vector for microplastics, and use SML sampling to assess microplastic trapping in a temperate marsh system in Southampton Water, UK. The SML is known to concentrate microplastics relative to the underlying water and is the first part of rising tidal waters to traverse intertidal and upper tidal surfaces. Sampling a salt marsh creek at high temporal resolution allowed assessment of microplastics in-wash and outflow from the salt marsh, and its relationship with tidal state and bulk suspended sediment concentrations (SSC), over spring and neap tides. A statistically significant decrease in microplastics abundance from the flood tide to the ebb tide was found, and a weak positive relationship with SSC observed.

Highlights

Microplastics are contaminants of increasing global environmental concern
The estuarine filter comprises a number of mechanisms, including vegetative trapping and particle flocculation, which moderate the supply of sediment and contaminants to the sea
Suspected microplastic morphology was dominated by fibres, with over 700 fibres observed and three fragments

Summary

Introduction

Microplastics are contaminants of increasing global environmental concern. Estuaries are a major transport pathway for land-derived plastics to the open ocean but are relatively understudied compared to coastal and open marine environments. Between 1.15 and 2.47 million tonnes of plastic debris of any size larger than 300 μm is estimated to be transported by r ivers[3] Due to this large plastic throughflow, estuaries are recognised as an important transport pathway from land to sea for microplastics[8]. Relatively understudied compared to beach and open marine environments with respect to both macro- and micro-plastics[10,11], despite their likely importance for microplastic land-sea transfer and their ecological importance. Estuarine habitats such as salt marshes and mudflats are potentially more favourable for the deposition of microplastics over high-energy environments such as sandy b eaches[12]. As vegetation effectively traps sediment and macro debris, it has recently been suggested that wetland vegetation may be an effective trap for m icroplastics[26]

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