Differentiating littering, urban runoff and marine transport as sources of marine debris in coastal and estuarine environments

Abstract

Marine debris is a burgeoning global issue with economic, ecological and aesthetic impacts. While there are many studies now addressing this topic, the influence of urbanisation factors such as local population density, stormwater drains and roads on the distribution of coastal litter remains poorly understood. To address this knowledge gap, we carried out standardized surveys at 224 transect surveys at 67 sites in two estuaries and along the open coast in Tasmania, Australia. We explored the relative support for three hypotheses regarding the sources of the debris; direct deposition by beachgoers, transport from surrounding areas via storm water drains and coastal runoff, and onshore transport from the marine system. We found strong support for all three mechanisms, however, onshore transport from the marine reservoir was the most important mechanism. Overall, the three models together explained 45.8 percent of the variation in our observations. Our results also suggest that most debris released into the marine environment is deposited locally, which may be the answer to where all the missing plastic is in the ocean. Furthermore, local interventions are likely to be most effective in reducing land-based inputs into the ocean.

Microplastic Distribution at Different Sediment Depths in an Urban Estuary

“…The site is not subject to large scouring events, thus any deposition is likely to remain in place. In addition, the site is much closer to sewage and stormwater outfall drains, which we found to be sources of plastic pollution in previous work (Willis et al, 2017). This result is similar to those found in other studies, which found higher numbers of plastics at sites closer to storm drain outfalls (Duckett and Repaci, 2015;Horton et al, 2017).…”

Adapting Coastal Collection Methods for River Assessment to Increase Data on Global Plastic Pollution: Examples From India and Indonesia

“…Whether a study from Europe describing how floating macro-plastics from the Rhone reach the Mediterranean (Castro-Jiménez et al, 2019) or research from Indonesia suggesting how rivers transport land-based plastic to the ocean (van Emmerik et al, 2019), the literature is replete with examples. In a comprehensive study testing hypotheses for how debris reaches oceanic systems, Willis et al (2017) find that most debris comes from local sources. The Stemming the Tide report confirms that rivers bring debris from upstream communities to coastal areas (Ocean Conservancy, 2015).…”

A Trip Upstream to Mitigate Marine Plastic Pollution – A Perspective Focused on the MSFD and WFD

“…A number of studies argue that rivers and terrestrial waterways facilitate the transport of discarded plastics from land to the ocean (Colton et al, 1974;Sheavly and Register, 2007;Munari et al, 2016;Willis et al, 2017;Crosti et al, 2018). Lebreton et al (2017) estimated that river systems carry between 1.15 and 2.41 million tonnes of plastic litter to coastal and marine environments every year, with around 80% of MPP coming from land-based sources.…”