Study finds plastic is changing the behaviour of the world’s river sediment

A University of Leicester expert has led a study which has found plastic pollution is changing the way riverbeds behave.

Dr Catherine Russell, together with colleagues from Leicester, the University of Loughborough, and Penn State University in the US, discovered plastic particles in waterways affect the way sediment moves along sandy riverbeds.

The team found that if sediment on a riverbed is contaminated with plastic, it changes how it moves downstream, compared to a plastic-free riverbed.

The research led the team to establish a novel branch of sedimentology which looks at the interactions between plastic particles and sediment.

“We did not anticipate such profound results, it opens a new chapter of unknowns regarding how plastic pollution is affecting our rivers and landscapes,” said Dr Russell, who is a Fulbright-Lloyd’s of London Scholar and an Honorary Fellow in Leicester’s School of Geography, Geology, and the Environment.

“Previously, we assumed plastic to travel passively through rivers, steadily moving downstream in the water or along the riverbed. Yet we find that plastic is not passive on the riverbed and is actually changing the riverbed dynamics. This will not just be different in natural systems, but anywhere that plastic and sediment co-exist, such as drains, conduits, and pipes. We find that plastic in riverbeds locally increases the erosion of sand, which therefore increases the amount of sand suspended in water, which means that riverbeds are changing shape, in places becoming more eroded, and in other places becoming flatter. Our findings highlight an important new factor to consider when assessing the extent of how plastic is impacting our landscapes, and its long-term consequences.”

The fundamental processes within sedimentology, a sub-discipline of geology, underpin all natural system dynamics, yet most plastic has markedly different properties to sand, clay, or gravel. This is the first study showing plastic particles on a sandy riverbed to be effecting this kind of change and we still have a lot to discover.

Dr Russell says is time to change the way we consider the impact of plastic in fluvial systems in exploring contaminated riverbed processes. This new knowledge of riverbed processes will be important to geography, earth science, hydraulic engineering, ecology, and environmental management.

This new branch of sedimentology is a timely one, as scientists continue to discover how we have, and continue, to impact Earth. In particular it is notable for the ongoing discussion on the Anthropocene – an unofficial unit of geologic time, used to describe the most recent period in Earth’s history when human activity started to have a significant impact on the planet’s climate and ecosystem.