Debris Pathways from Source to Sea: The impact of land use and the Covid-19 pandemic on debris in stormwater networks

Brie Sherow1, Emma Johnston1, Jordan Gacutan1, Heidi Tait1, Graeme Clark1

1University of New South Wales


To understand how debris enters our ocean and to manage it effectively we need to identify pathways of debris between source and sea. One potential pathway for debris is through stormwater drainage, which is sometimes managed by gross pollutant traps (GPTs). Debris caught in traps provides an indication of the magnitude of this pathway and the types of debris entering the marine environment via stormwater. Here we present the first large-scale study of debris caught in gross pollutant traps in Australia. The 12-month study (October 2019-2020), conducted across six local government areas (LGAs) in Greater Melbourne, also provides a unique opportunity to examine trends during one of the world’s strictest Covid-19 lockdowns. Through the efforts of citizen scientists, NGO’s, university, and government; we assessed the influence of differing land use zones (e.g., industrial, shopping centre) and Covid-19 lockdowns on the types and abundance of debris recovered from stormwater drains. The high item counts were cigarette butts and plastic packaging in areas of high foot-traffic (e.g., CBD, shopping centres), although debris totals decreased roughly 40% during lockdown. In contrast, micro-debris (<5mm, such as primary and secondary plastics), were most abundant in industrial precincts and totals increased during lockdown. The information gathered from regular monitoring of GPTs could form the basis of targeted litter reduction schemes and our understanding of debris sources and pathways.