A study led by researchers from the US Smithsonian Institution and the UB reveals that reducing single-use plastic is essential for protecting coastal ecosystems. Floating litter has also invaded Chesapeake Bay, the largest estuary in the United States and one of the most important in the world. Food and beverage packaging from at least 52 different companies — particularly single-use plastics with a lifespan of less than a year — are increasingly abundant in its tidal marshes, which cover an area of more than 1,200 km², spread along the estuary’s 18,800 km shoreline. Much of the floating litter found originates from urban areas and from careless behaviour linked to everyday consumption patterns. In fact, there is also litter that has been discarded directly in parks and recreational areas, or from boats.
Floating litter degrades the environmental health of the areas where it accumulates, and can affect local wildlife and processes of great ecological value to ecosystems, such as gas exchange, biological activity and carbon storage.
These are some of the conclusions of an article published in the journal Marine Pollution Bulletin on the Chesapeake Bay. The study represents one of the few detailed analyses of macro-litter pollution (i.e. litter larger than 2.5 cm) in tidal marshes on a regional scale worldwide. The prevalence of plastic waste is not unique to estuarine environments. Plastics are also the predominant type of waste found in mangroves, on beaches, in dunes and in other coastal ecosystems in various countries. Reducing single-use plastic waste is therefore a key measure for protecting coastal ecosystems.
The lead author of the study is Ostin Garcés-Ordóñez, a postdoctoral researcher in the Life on a Sustainable Planet (LSP) and MarineGEO programmes at the Smithsonian Institution, and a member of the Consolidated Research Group in Marine Geosciences (Gmar) at the UB’s Faculty of Earth Sciences. Co-authors include Professor Miquel Canals, director of the UB’s Chair on Sustainable Blue Economy and a founding member of Gmar; Martin Thiel, André Rovai and Genevieve Noyce, researchers at the Smithsonian Environmental Research Centre (SERC); and Rachel Collin, scientist at the Smithsonian Tropical Research Institute (STRI, Panama).
Where does floating plastic accumulate?
The study focuses on the upper intertidal zone reached by the highest tides, where wrack deposits — that is, accumulations of plant debris such as trunks, branches, leaves or roots carried by the tidal flow — accumulate. Beach debris provides food, energy and shelter for various forms of marine life, although nowadays, it contains considerable amounts of litter, particularly floating plastics.
One of the most significant findings of the study was the discovery of areas where floating plastics tend to accumulate in the tidal marshes of the Chesapeake Bay.
“Much of the litter originating from urban areas never reaches the ocean but is retained within Chesapeake Bay by estuarine circulation. The dense vegetation of these marshes, dominated by tall reeds of the Phragmites genus, traps part of the litter transported by tides, which then mixes with natural wrack components,” says Ostin Garcés-Ordóñez, who completed his doctoral thesis at the UB a few months ago.
“Macrolitter becomes concentrated in tidal marshes, particularly in areas sheltered from strong currents and wave action”, notes Garcés-Ordóñez. “This allows plastic litter to remain in the same locations for long periods, gradually fragmenting into smaller pieces, including microplastics, that eventually become buried in the soils of the marsh. As a result, the high-tide zone functions not only as a critical area for the temporary accumulation of litter, but also as a long-term reservoir of plastic pollution.”
Warning about the impact of single-use plastics
The Chesapeake Bay watershed, covering an area of approximately 166,000 km², is home to more than 18 million people, living in both urbanized and densely populated areas and in predominantly rural areas. This has made it possible to examine the impact of different types of human activity, at varying levels of intensity, on the quantity and types of litter reaching the tidal marshes.
“The zones with the highest litter accumulation in Chesapeake Bay are those located closest to major urban centers and characterized by dense vegetation”, says Miquel Canals, professor at the UB’s Department of Earth and Ocean Dynamics. “The highest concentrations of macrolitter, particularly floating plastics, were found in the inner estuary, especially in areas influenced by metropolitan regions such as Baltimore, where 2.86 million people live.”
“Distance from population centers is the factor that best explains the amount of litter found at the different sampling sites: the closer a marsh is to urban areas, the greater the litter accumulation”, adds Canals.
The study also identified a clear geographic pattern in litter accumulation. “The northern, inner estuary, receives larger amounts of litter carried by rivers. In contrast, the southern, outer estuary is connected to the Atlantic Ocean and contains a relatively higher proportion of litter associated with maritime activities”, notes Martin Thiel, managing director of the MarineGEO Program at SERC and also professor at Universidad Católica del Norte (Chile).
“Overall, however, more than 50% of the litter accumulated in marsh wrack deposits throughout the Chesapeake estuary originates from land-based human activities”, adds Thiel. “The main source identified was poor waste management practices, including carefree discarding of single-use plastics associated with consumption outside home.”
Chesapeake, a natural laboratory
The Chesapeake Bay is an exceptional large-scale natural laboratory for studying the origin of litter and understanding why certain types of waste accumulate more in some places than in others. Complementary studies are currently being carried out to better understand the co-accumulation of litter and organic debris, mainly of plant origin, as well as its potential impacts on the ecosystem services provided by marshes.
In the northern inner estuary, where urban centres align with high proportions of litter in wrack deposits, priority must be given to environmental management, monitoring and the early interception of floating litter before it accumulates in tidal marshes. Furthermore, future research is needed to better understand the extent to which, and the ways in which, the accumulation and fragmentation of plastic items in wrack deposits affect the health and environmental services provided by marshes.
The results provide clear guidance for addressing the problem identified. “All sectors of society can contribute to reducing plastic pollution: consumers should properly dispose of waste through established collection and treatment systems, companies should develop more sustainable and reusable packaging, and policymakers should support these efforts through stronger regulations and more effective enforcement mechanisms,” the team states.
“Educational institutions, environmental organizations, and society as a whole must continue promoting greater environmental awareness and more responsible consumption habits. The United Nations Global Plastics Treaty, currently under negotiation, represents a major opportunity to advance meaningful solutions to a largely preventable global problem,” conclude the researchers.