Cleddau farmers could save £1 million a year on phosphorus fertiliser, as major Lancaster University study identifies cause of river pollution 

A major new study by Lancaster University has identified the underlying cause of phosphorus pollution in the Cleddau Special Area of Conservation, Wales' protected river system with the highest phosphorus failure rate. 

 The research found that farms across the Western and Eastern Cleddau catchments generate a combined annual surplus of around 360 tonnes of phosphorus, while analysis by The Cleddau Project, verified by Lancaster University, found that farmers across the catchment could save up to  £1.08 million annually on phosphorus fertiliser purchases if manure applications were aligned more closely with crop requirements.

 The study concludes that this agricultural  surplus is a primary driver of phosphorus pollution in the Cleddau and identifies practical measures that could improve river health while strengthening farm resilience and profitability.

 The study was commissioned by The Cleddau Project and West Wales Nutrient Management Board to provide an independent scientific assessment of nutrient pressures within the catchment and help build consensus around the actions needed to restore river health.

 Rather than focusing solely on pollution incidents, slurry storage or nutrient management plans, the research identifies a long-term nutrient imbalance at the heart of the problem, with more phosphorus entering the catchment each year than is being removed through food production.

 Crucially, the study also identifies a practical route to recovery. Researchers found that the phosphorus contained in animal manures produced within the catchment would be sufficient to meet crop requirements if distributed according to need. In theory, this means little or no additional inorganic phosphorus fertiliser should be required.

 The model suggests that reducing phosphorus fertiliser imports by around 50% and increasing exports of surplus dairy manure could reduce the annual phosphorus surplus to near zero. Over time, this could cut phosphorus losses from agriculture to rivers by around 50%, helping improve water quality and accelerate recovery of the Cleddau river system.

 Using the internationally recognised RePhoKUs nutrient modelling system, researchers analysed nutrient flows across the catchment and found that phosphorus imported onto farms in feed and fertiliser significantly exceeds the amount exported in agricultural products.

 According to the study, around 360 tonnes of surplus phosphorus are generated across the combined Western and Eastern catchment every year. Researchers estimate that approximately 23 tonnes are lost directly to rivers annually, while the remainder accumulates in soils, creating a growing reservoir of so-called “legacy phosphorus” that can continue polluting waterways for decades.

 Dr Martin Samphire, a soil scientist working for the West Wales Nutrient Management Board, said, “We welcome this report, which highlights a fundamental but neglected issue in our food system: excess phosphorus building up in soils and driving river pollution. While focused on the Cleddau, its findings have national relevance.” 

 The findings help explain why the Cleddau Special Area of Conservation has the highest phosphorus failure rate of any protected river system in Wales.

 Researchers also found that decades of nutrient surpluses have created a substantial reservoir of historic phosphorus within catchment soils. In the Western Cleddau, around 50% of phosphorus entering the river is estimated to come from this legacy build-up rather than recent applications.

 Importantly, the study found higher river phosphorus loads in areas with higher agricultural nutrient surpluses. Detailed analysis of river phosphorus concentrations with flow also found that over 80% of the river phosphorus load could be attributed to agriculture during periods of high flow. 

 The scale of the surplus also has significant economic implications. The model estimates that farmers purchase around 361 tonnes of elemental phosphorus each year, equivalent to approximately 1,805 tonnes of commercial fertiliser. Analysis by The Cleddau Project, verified by Lancaster University, found that these purchases are worth approximately £1.08 million annually at current prices.

 The findings come at a time of growing uncertainty in global fertiliser markets and national food security. Geopolitical instability and volatile energy prices have contributed to fluctuations in fertiliser costs, placing additional pressure on farm businesses already facing rising costs and tightening margins.

 Supporters of the study say the findings demonstrate that improving nutrient efficiency could help farmers become more resilient to future price shocks while simultaneously reducing pressure on rivers.

Ric Cooper of The Cleddau Project said, “For years there has been debate about what is driving phosphorus pollution in the Cleddau. This study provides robust scientific evidence that a substantial phosphorus surplus is building up across the catchment and that it is a major contributor to river pollution.

 “At a time of rising input costs and volatile fertiliser markets, improving nutrient efficiency offers a genuine win-win: helping farmers reduce costs and improve resilience while restoring the health of one of Wales' most important river systems.”

CEO of River Action James Wallace said, “This research provides some of the clearest evidence yet that nutrient surpluses on farmland are driving river pollution.

“Importantly, it doesn't just identify the problem. It shows there is a practical pathway to reducing phosphorus pollution while improving nutrient efficiency on farms. The lessons from the Cleddau could help tackle nutrient pollution in livestock-intensive catchments across Britain, while improving farm financial viability and lowering the soaring costs of food.

 “At a time of worrying food and energy insecurity, we need the Government and industry to help farmers feed the nation, treating manure as valuable nutrients and stop relying on imported fertilisers.

 The findings come as nutrient footprinting gains increasing attention across the farming sector.

 In June, First Milk announced the rollout of nutrient footprinting and water risk mapping across its 700 member farms throughout the UK. The programme enables farmers to measure nutrient surpluses at farm-gate level, helping identify opportunities to improve efficiency while reducing environmental pressures.

 One of the farms participating in the programme is the Clements family, who supply First Milk from a 190 cross-bred  grass-based herd on the banks of the Eastern Cleddau.

Di Clements  said, “We have always tried to do the right thing to minimise losses of excess nutrients to water, but without evidence we've previously had no idea what those losses might be.

 “We are really looking forward to receiving our nutrient footprint from First Milk soon so we can use the data to target those areas that may be having an impact on river health and identify what steps we can take to address this.

 “If we can reduce the amount of expensive fertiliser we use without losing production, and at the same time improve water quality and ultimately the river's health, then everyone is a winner.”

 Early analysis from First Milk suggests that lower nutrient-footprint farms can achieve similar levels of milk production to higher nutrient-footprint farms, indicating that productive farming and improved environmental outcomes can go hand in hand.

Mr Cooper added, “For the first time, we can see the problem from both directions. Lancaster University has quantified the surplus at catchment scale, while nutrient footprinting allows farmers to measure it at farm scale.

 “That creates the possibility of a genuine win-win: improving river health, reducing waste and helping farmers become more resilient in an era of rising costs and growing environmental pressures.”