Using an innovative Catchment Nutrient Balancing (CNB) approach to improve river water quality: A case study from rural sub catchment in Cumbria, United Kingdom

Abstract

Nutrient pollution in river catchments is of significant concern in the UK, particularly from excessive phosphorus, and meeting water quality objectives requires addressing multiple sources of pollution. This study aimed at piloting a Catchment Nutrient Balancing (CNB) approach in the Calthwaite Beck rural catchment, to achieve the local water company's Water Framework Directive (WFD) objectives for phosphorus reduction. CNB is an innovative flexible permitting approach, enabling water companies to reduce loads associated with their wastewater treatment works (WwTW), by working with other sectors to integrate WwTW and catchment solutions. This approach balances phosphorus load reductions across these solutions to achieve regulatory requirements and wider benefits. It promotes collaboration, innovation and systems-thinking, by encouraging water companies to collaborate with various stakeholders to integrate solutions, develop new technologies, and adopt holistic rather than siloed, approaches. This study was the first example in the UK, and is still one of the few, using CNB to meet regulatory phosphorus targets. It involved combining innovative treatment (Polonite®) at Calthwaite WwTW with farming interventions in the catchment to reduce phosphorus. The study successfully demonstrated the effectiveness of an integrated approach at achieving water quality objectives: over a three-year period, phosphorus reduction levels in the catchment achieved an annual average of over 65%, surpassing the 9% annual reduction target, with Calthwaite Beck's ecological status improving from “poor” to “moderate”. The findings highlight the importance of collaborative engagement, particularly with regulators, farmers and catchment partners, to improve water quality and deliver wider benefits.