Striving for environmental balance: nutrient neutrality to futureproof the development pipeline

Nutrient neutrality aims to protect water bodies by avoiding any increase in nutrient levels.

By Wendy Furgusson, Associate, Environment and Health, Ramboll

With Natural England’s recent changes to planning policy causing a reduction in the number of new homes built from 240,000 a year in 2018-19 to a projected 111,000 by 2025, awareness of nutrient pollution as a problem is becoming more widespread. In the Lake District, for example, swimmers have been warned of toxic blue-green algae whilst dog walkers in Devon were told to keep their pets away from poisonous ponds. In an era where environmental conservation takes centre stage, the importance of managing nutrient pollution and implementing effective mitigation strategies cannot be overstated.

A myriad of potential solutions are available for developers seeking to balance construction plans with the need to protect ecosystems and communities. Among these, the construction of wetlands and collaborative efforts with wastewater treatment companies have shown promising results. However, it is widely recognised that the responsibility cannot rest solely on the shoulders of developers and that a comprehensive and holistic approach to nutrient neutrality is imperative.

Defining nutrient neutrality
Nutrient neutrality is an approach that aims to balance nutrient inputs and outputs within a defined area, typically related to land development and occupation. It involves avoiding any net increase in nutrients, such as nitrogen and phosphorus to protect water bodies and ecosystems from excessive nutrient pollution.

In the context of land development, nutrient neutrality focuses on managing the nutrient runoff from developed areas, such as residential or leisure accommodation, as well as treatment of wastewater to prevent adverse impacts on water quality. This is particularly important because excess nutrients, when carried by stormwater runoff or treatment works discharge, can contribute to water pollution, leading to issues like eutrophication and harmful algal blooms.

A growing concern
Initially Natural England’s focus of attention was on nitrogen in the Solent and Kent regions, though nutrients like phosphorus were already being assessed in the Avon catchment. The issue has since exploded, with an increase in the number of local authorities falling under the Natural England planning constraints. The geographical areas falling under these planning requirements have shifted the balance of concern to phosphorus rather than nitrogen. This is especially true in Wales and the northwest of England where phosphorous is the key contaminant of concern with its detrimental impacts on water quality and ecosystem health.

Government intervention: identifying the problem
In March 2022, the Government launched a policy paper to investigate the intricacies of the spiraling problem and identify actions needed to tackle the issue. They acknowledged that pollution was stifling planning permission approval, subsequently halting house delivery across 74 local planning authorities. With a view to support sustainable development and achieve their ambition of building 300,000 new homes each year by the mid-2020s, the Government pledged to reduce pollution at source.

The paper announced a series of initiatives to tackle the issue and safeguard the environment. To hasten the mitigation process for developers, a £30 million nutrient credit scheme was introduced alongside a package of clear guidelines. Alongside this, the Levelling Up and Regeneration Bill called for water companies to upgrade wastewater treatment works to restore protected sites and tackle pollution.

However, according to evidence given to a House of Lords committee in March 2023 by James Stevens, Director of Cities at the Home Builders Federation, housebuilders are being forced to spend up to £25,000 per home on mitigation strategies – implying alternative solutions are urgently needed to aid developers.

Constructed wetlands can help mitigate phosphorous but are not always practical to do.

Achieving nutrient neutrality
Mitigating on-site nutrient levels presents a greater challenge for phosphorus compared to nitrogen. Nitrogen levels can be effectively reduced by implementing land use changes, such as converting farmland into woodland. However, mitigating phosphorus levels proves more challenging as alternative land use alone may not achieve the necessary reduction targets.

However, harnessing the power of constructed wetlands can be an effective approach for mitigating phosphorus, whether originating from surface water runoff or outfall from wastewater treatment facilities. In cases where individual development sites possess sufficient space, incorporating constructed wetlands into these sites not only aids in phosphorus mitigation but also offers additional advantages in terms of surface water runoff management and promoting biodiversity net gain.

Whilst local nutrient credit trading schemes have been available in the Solent catchment for more than 2 years, it was only In March 2023 that developers were able to apply for the first credits offered as part of the Natural England mitigation scheme.  These were to offset the impact of development in the Tees catchment and support creation of new wildlife habitats, such as wetlands in an effort to unlock the development of 1,600 homes. Stevens noted this ‘market-based solution’ was a cheaper answer to the nutrient neutrality problem, costing around £3,500-£4,000 per home, and should be expanded country-wide.

In addition to this, local authorities are also working with water companies and statutory regulators to reduce permit levels for wastewater treatment works, requiring works to treat outfall to a higher level so the amount of residual nutrients reaching surrounding sites is reduced.

Given the space needed to construct wetlands, they are unfortunately not a viable option for all developers and wider, more strategic solutions are needed. Scotland faces similar challenges regarding nutrient neutrality, but the Scottish Government has taken a different approach to England and Wales. They employ a life cycle analysis-type methodology known as the Scottish Nitrogen Balance Sheet, which considers multiple factors such as development, the economy, and agriculture. Unlike the planning regime constraints observed elsewhere, Scotland’s approach allows for a more comprehensive assessment and response to nutrient-related issues – could this be the way forward for the rest of the UK?

The road ahead
The challenges of achieving nutrient neutrality and implementing effective mitigation schemes are multifaceted and require a comprehensive, often multi-party approach. The impact of nutrient pollution on water bodies and ecosystems cannot be ignored, and addressing this issue is not only crucial for sustainable development and environmental conservation but also to bolster the country’s housing stock.

Despite mitigation techniques such as constructed wetlands showing promise, their viability is limited by space requirements. Collaboration between developers, local authorities, water companies and regulators is essential to implement effective strategic mitigation strategies and reduce the impact of nutrient pollution. Most importantly, we must adopt a holistic methodology that considers multiple factors, providing a comprehensive assessment and response to nutrient-related issues.

As we move forward, it is essential to continue exploring innovative approaches, promoting sustainable farming practices, enhancing wastewater treatment methods, and raising awareness through educational campaigns. Only through concerted efforts and a combination of strategies can we achieve nutrient neutrality and safeguard our ecosystems for future generations.