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The wide Mersey Estuary in north west England

A new study examining nitrogen pollution in the Mersey Estuary over the last 200-years has found concerning levels of sewage in the water today – and our experts say immediate action is needed to clean it up. 

The River Mersey, in north-west England, was once dubbed the most polluted river in western Europe.   

And new research by geochemists Freya Alldred and Professor Darren Gröcke has found that despite previous efforts to clean it up, the river and its estuary remain heavily polluted by sewage nitrogen.   

Time capsules 

The researchers used herbaria – dried seaweed – from the collection at the World Museum, National Museums Liverpool, to investigate nitrogen pollution in the Mersey Estuary over the past 200-years.   

Herbaria act like time capsules, capturing in its tissues the environmental conditions it was growing in.   

In the study, published in the journal Environmental Science: Advances, the Durham team analysed parts of herbaria seaweed for stable nitrogen isotopes using our Stable Isotope Biogeochemistry Laboratory (SIBL), Department of Earth Sciences.   

Nitrogen isotope data was then used to identify historical changes in industrial and/or sewage pollution.   

The research indicates that sewage pollution in the Mersey Estuary is increasing to levels only last seen in the record from the 1980s, when a public outcry sparked a major clean-up campaign.    

The researchers suggest this represents an ongoing failure to improve the UK’s water quality by reducing sewage discharges into our waterways.   

Mapping out pollution 

The study is part of Professor Gröcke’s work to produce a comprehensive map of modern UK coastal and estuarine nitrogen pollution.   

It is the first time that herbaria have been used in this way to paint an overall picture of the cleanliness of a country’s watercourses. 

It could be used to help local authorities and interested parties identify nitrogen polluted areas and take appropriate action to reduce the environmental impact.   

Professor Gröcke said: “It's clear that processes over the last 200-years have led to a gradual decline in the health of our environment and, although we are the cause, we are also the solution.”  

Find out more 

Earth Sciences at Durham 

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A herbaria (dried seaweed) sample

Herbaria (dried seaweed) sample used in the study