Plastic pathways – the dramatic journey from source to sea

Whichever way you look at it, our rivers and coastal waters are inextricably linked. A plastic bottle casually tossed away in the middle of the country, blown on the breeze into a river tributary will make its way, over time to open water, by which time it’ll be in many tiny pieces after being bashed around and broken down. We’ve been working with Salmon & Trout Conservation to highlight plastic’s destructive journey – from source to sea.

Lauren Mattingley

Science Officer Salmon & Trout Conservation

Salmon & Trout Conservation Graphic

Plastic Pathways

The continuous increase in synthetic plastic production and poor management in plastic waste has led to a tremendous increase in its presence in our water environments. Plastic does not decompose, it simply gets smaller and smaller. Consequently, plastic particles less than 5 mm in size - commonly defined as microplastics - are produced and persist in both seawater and freshwater systems. Around 80% of marine microplastics come from freshwater run-off, meaning there is a whole period where microplastics persist in rivers before they are flushed into the ocean.

Where do microplastics go?

There are few watery places untouched by plastics, microplastics have been found even in the deepest parts of our oceans. Similar to ocean currents, rivers have their own distinct flow ‘fingerprint’, whereby no two rivers will transport material exactly the same way. A lot of this uniqueness comes from human interference - wherever we abstract water or build structures, we change a rivers flow regime.

This regime has a big influence on the journey of microplastics and determines what quantities remain in rivers and what quantities are delivered to oceans. In relatively fast flowing rivers with no obstacles, microplastics can be transported directly and rapidly downstream, straight into marine environments. However, in rivers with lower flows, or places where flow is disrupted (structures like dams and weirs) it is more likely that plastics will sink and persist in river sediments. Weather events can also facilitate or impede movement of microplastics. For example, heavy rain can trigger flood events that flush out plastic particles bound up in sediments, speeding up delivery to the ocean.

Sadly, the ultimate fate of microplastics, regardless of their delivery route, is usually in the digestive tracts of wildlife. These plastic particles are easily mistaken for food and ingestion can mimic fullness and deliver harmful toxins to the animals that eat them. From riverfly insects to whales, plastic pollution is disrupting the natural balance of our ecosystems through its influence on food chains.

Working together

It is essential that to protect our oceans and rivers we stop plastics at source. We are excited to be working with MCS to raise awareness about the connectivity of plastics from source to sea. Their work on changing policy around single-use plastics has never been more important and we will be adding our voice to help strengthen the case for protection of our freshwaters, as well marine.

We have developed the infographic (above) to help teach more people that when it comes to plastic, rivers and oceans go hand in hand. Only by understanding the dynamics of microplastics in freshwater, will we be able to effectively measure and manage the contribution to our oceans, in turn protecting marine and freshwater life.

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