Housing developments and pollution control

Algal bloom
Housing developers argue for increased clarity on nutrient management in Special Areas of Conservation.


The Environment Agency and Natural England have put Nutrient Management Plans (NMPs) in place in England’s sensitive catchments - including protected Natura 2000 sites

Producing NMPs for Natura 2000 sites helps to provide evidence for Habitats Regulations Assessments which might be required in relation to development plans and reviews of discharge consents. NMP’s also provide evidence that underpins the strategy to achieve the targets arising from the Habitats Directive, Birds Directive and Water Framework Directive.

An Improvement Programme for Natura 2000 sites (IPENS) has been developed by Natural England which includes a Site Improvement Plan (SIP) for each Natura 2000 site. Eight of these site improvement plans include an NMP. These provide a mechanism for tackling water pollution where excessive phosphorus and or nitrogen loading requires a combined approach that addresses point discharges and diffuse sources. 

Special conservation

The River Avon Special Area of Conservation (SAC) is a Natura 2000 site with an NMP, where phosphorus is preventing favourable conservation status being achieved across the catchment. 

The River Wye SAC has reaches where the levels of phosphate exceed the target level in the conservation objectives. Other examples of sites with an NMP include the River Clun and River Mease SACs and Poole Harbour Special Protection Area (SPA).

The River Mease SAC’s excessive levels of phosphate are preventing the achievement of favourable condition, and at Poole Harbour SPA, increasing nitrogen levels from sewage and agriculture are contributing to the growth of algal mats in the harbour,restricting food for wading birds and smothering estuarine habitats. 

Meanwhile, the River Clun is designated as a SAC for freshwater pearl mussel. Since 1995, surveys have shown that the population of freshwater pearl mussel is non-functioning due to pollution issues from phosphorus, nitrogen and sediment. 

Pollution control

Pollution control for the above NMPs includes measures for both point sources and diffuse sources

For diffuse sources, there are various measures such as integrated soil, water and nutrient management plans for farms; encouraging the use of winter storage reservoirs within the horticultural sector; rectifying sewer misconnections and reverting to semi natural vegetation.

At point sources, examples of measures include upgrading sewage treatment works to strip out nutrients; reducing phosphorus emissions from fish farms and cress farms; preventing infiltration to the sewer network; reducing discharges from Combined Sewer Overflows (CSOs) and examining the potential to retrofit Sustainable Urban Drainage Systems (SUDS).

New development

An NMP is a potential barrier to the construction of housing and other infrastructure in these catchments, particularly where the development could increase nutrient loads in sewage. 

Given the urgent need for new housing in the UK, this is a real concern. However, if the resulting nutrients can be removed at the sewage treatment works or be offset through measures to reduce diffuse pollution, developments can still proceed. 

Potential restrictions vary. For example, at the River Mease, new development can only take place if it contributes to the Developer Contribution Scheme so as to be phosphate neutral. Developer Contribution Scheme contributions from residential development coming forward in the first development window are calculated by the size of the dwelling and how sustainable it is. 

At Poole Harbour, new development can only take place if it mitigates 25 percent of the additional nitrogen it produces (Wessex Water is expected to remove the other 75 percent at sewage treatment works). 

A supplementary planning document (SPD) lays out the process for councils to secure mitigation from Community Infrastructure Levy (CIL) and Section 106 agreements.

Increased clarity 

The SPD provides examples of nitrate loads for different development types and mitigation options. The developer has up to four choices for the Section 106 agreement, including to provide alternative technologies to remove the remaining nitrogen, increase the size of Suitable Alternative Natural Greenspaces (SANGs) on agricultural land, agree with the council a change to the management of agricultural land in the wider landholding in perpetuity, and/or purchase agricultural land elsewhere within the catchment and use it for mitigation.

The River Avon NMP originally allowed development within the existing headroom of sewage treatment works. However, the Environment Agency and Natural England subsequently advised that development must be phosphate neutral as targets in the NMP were unlikely to be met by 2021. 

Post 2025, it is assumed that upgraded sewage treatment works will remove additional phosphorus. A joint Memorandum of Understanding provides for interim mitigation which will be funded primarily through CIL paid by developers, 

Specific schemes to facilitate development in a controlled manner, such as those for the River Mease, the River Avon and Poole Harbour, are important because they provide clarity to developers on what measures they need to adopt to comply with the NMP.

However, experience suggests that there are still areas of uncertainty for developers, for example around the level of reliance that can be placed on water companies to upgrade sewage treatment works beyond the current Asset Management Plan (AMP) and on the level of nutrients that can be assumed to be removed by different offsetting measures. 

Increased clarity on these issues is required so that the urgent need for new housing can be met, while fully protecting these important aquatic habitats. 

This Author 

Dr Steve Mustow is director and head of environmental planning at WYG.