Utrecht University: Up to 30 thousand kilos of litter washed up on Dutch beaches

Utrecht researchers have fully mapped out how much litter is washed up from the sea onto Dutch beaches, under which conditions it washes ashore and from where it originates. These insights make it possible to predict where and when litter will wash ashore, so that it can be cleaned up more effectively. The researchers at Utrecht University, in collaboration with Stichting De Noordzee, published their results yesterday in the scientific journal Ocean Science.

The researchers worked with a dataset of Stichting De Noordzee, consisting of six years of beach clean-ups, summer events where volunteers clean up litter on the beach. The data shows that at present, there are between seventeen thousand and thirty thousand kilos of litter on Dutch beaches. “That comes down to an average of 20 to 80 kilos of litter per kilometre of beach,” says Mikael Kaandorp, first author of the publication.


Litter predictions
By combining this information with weather data, the researchers were able to determine under which weather conditions large amounts of litter washes ashore. This even makes it possible to make predictions, says research leader Prof Erik van Sebille. “If, based on weather forecasts, you expect a lot of litter to wash ashore on a certain day and at a certain location, you can plan ahead to clean it up before it washes back into the sea. This is extremely important, because it is much easier to clean up litter on the beach than in the ocean.”

Origin
The researchers also studied where the washed-up plastic litter comes from. “We found a strong correlation between how old the plastic is and how far it has travelled,” says Kaandorp. “The newest plastic usually comes from the Netherlands, slightly older plastic from the Channel or the coast of England, and a small part comes from further away: France, or even Scotland.” It is easy to see from the type of plastic that there is a lot of fishing activity around the English Channel: about forty percent of the plastic waste on Dutch beaches originates from fisheries.

Castricum and Bergen
The study shows that the hotspot for beach litter in the Netherlands is the coast just to the north of Amsterdam, around Castricum and Bergen. Kaandorp: “In Zeeland, there is less ocean litter on the beach. The coastline there has a more irregular shape, and most of it is not directly adjacent to the North Sea. And we think that the litter washes back into the sea more easily, because the tide is more variable there.” There is also less litter washing ashore on beaches in the north of the Netherlands, including the Wadden Islands. “The ocean currents and winds near the Netherlands come mainly from the southwest. The Wadden Islands simply don’t have as much coastline oriented towards that direction.”

Despite these variations, the Netherlands is a relatively easy country to apply these analyses to, according to Van Sebille. “Our coastline is comparatively simple, it is a fairly straight line with mainly sandy beaches. The next step in the research is to apply our model to more complicated areas, such as the Galapagos Islands. Around that group of islands, the ocean currents are more complex, and the coastline there is much more irregular and varied in nature.”

Bad weather
Kaandorp does have an important footnote to make about the data used. “Beach cleanups are mainly organised when the weather is nice, so we don’t have that much data on the amount of litter on our beaches in bad weather conditions. This could mean that our model is less accurate for the winter season. So, we hereby call for more beach cleanups in autumn and winter.”


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