The Phosphate Conundrum

DHA's Tim Spicer provides an update on Natural England's advice note on the Stodmarsh Special Area of Conservation



It has now been nearly twelve months since Natural England issued their first guidance note to Kent planning authority, Canterbury City Council, in respect of the Stodmarsh Special Area of Conservation (SAC). DHA's Tim Spicer provides the latest update which is now affecting parts of Ashford, Maidstone, Canterbury and Folkestone & Hythe.

The advice stated that in light of recent monitoring of nutrient levels at the Stodmarsh SAC and Europeancase law[1], local planning authorities should not grant permission for residential development unless it can be demonstrated that the development is "nutrient neutral" in respect of phosphorous and nitrogen.

The issue arises principally from the treatment of human waste at wastewater treatment works that discharge to the River Stour and its tributaries. Whilst the treatment process makes the effluent discharged "clean" many of the works either do not remove phosphorous or nitrogen or do not have an appropriate limit imposed upon them. Too much dissolved phosphorous and nitrogen in an aquatic environment such as Stodmarsh, into which the Stour flows, causes eutrophication resulting in explosive algae growth and low oxygen levels which ultimately affect the insects, fish and birds which form the ecosystem of the lakes. Development which results in deleterious effects on a SAC is prohibited under The Conservation of Habitats and Species (Amendment) (EU Exit) Regulations 2019.

As we now know, Canterbury City Council was the first of several Kent authorities to be affected, with the list now including Ashford Borough Council,  Folkestone & Hythe District Council and Maidstone Borough Council which all fall partly within the wider Stour catchment. The Home Builders Federation estimate that this issue could affect up to 50,000 homes in the region over the next twenty years.

Whilst providing little comfort, Kent is not alone in this issue. A similar issue has been ongoing in Hampshire since 2019, albeit driven primarily by nitrates rather than phosphates and the issue is also now holding up several thousand houses in north Somerset. At present twenty five local authorities in England are battling this problem.

At a time like this one might expect central government to step in and help co-ordinate a way out of this and coerce what can only be described as a lack lustre waste treatment industry into action. To date however, central government have been slow to react and have made no commitment to intervening instead leaving it to local authorities to battle their way through the ever changing and somewhat ambiguous guidance from Natural England.

This leaves developers and local authorities with a number of costly and land hungry ways to try and mitigate the problem:

  • Converting farmland to woodland, offsetting the removal of nutrients applied to land against that generated by the proposed development
  • Creation of wetlands and reed beds to effectively "absorb" the nutrients in the water (on site or off site)
  • Installation of on-site treatment works

In addition to the above Canterbury City Council have announced that they are at a advanced stage with their strategic strategy which they hope to present to government over the coming months. We are currently working with Ashford Borough Councils property team to explore site specific and more strategic solutions. Folkestone & Hythe District Council are proposing a new wastewater treatment works and wetlands at their Otterpool allocation to facilitate their allocations in their emerging local plan. It is understood that these solutions will (where successful) help provide a solution for allocated sites only.

It is therefore clear that ultimately the solution will have to come from Southern Water, investment in infrastructure upgrades and regulations which obligate faster action to the problem in the wastewater industry. The question of when central government will step in remains.

DHA will keep you updated as and when any news in this regard occurs.

[1] Dutch Nitrogen cases (C-293/17 and C-294/17)

For more information call 01622 776226 or email:

Share this