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Dear Policy Team

New Forest Catchment and Geographical Scope for Nutrient Mitigation

Thank you for your recent enquiry (dated 9th April 2021) regarding the geographical scope for nutrient mitigation for development draining to the Pennington outfall and the New Forest river/stream outfalls, as currently set out within Natural England’s Solent nutrients guidance. Clarification was requested on this aspect of the guidance.

For historical context, the New Forest estuaries were classed at Good Ecological Status for macroalgae under Water Framework Directive (WFD) assessment by the Environment Agency (EA) at the time of SSSI condition assessments up to 2016. The Solent was considered the major influence for nitrogen at the estuaries, however EA survey data did show some areas of dense algal mats further up the Beaulieu estuary. SSSI condition assessments for the Beaulieu estuary identified a future risk of failure of favourable condition due to the nutrient status within the water environment.

More recent WFD assessment (2019) released by the EA of opportunistic macroalgae abundance has downgraded the Lymington and Beulieu estuaries combined waterbody to Moderate status. This new evidence indicates nitrogen influence from the landward catchments and/or sewage treatment works (STW) discharges and strengthens the need for development draining to these areas to locate mitigation within those river catchments as the preferred option. (However please note further analysis of the raw data is required to establish if the dense macroalgal mats at Moderate class are restricted just to the Beulieu estuary or both Beaulieu and Lymington estuaries.)

The other New Forest streams draining into the Solent (including Avon Water, Danes Stream, Dark Water and Sowley Stream) have small catchments with little or no estuary, with little data on macroalgae abundance, and so the case for delivering nutrient mitigation for new development discharging wastewater specifically in these freshwater catchments is not considered strong. It is also recognised that the potential for adequate mitigation land across this area may be restricted either because the catchments are small and/or much of the catchment has no or low nitrogen input from agricultural activities (as much of the area is designated habitat). Therefore, it is considered appropriate that the geographical scope for mitigation can be widened for developments draining to these catchments to include the Western Yar and Newtown catchments on the Isle of Wight.

Evidently, more work is needed on refining analysis of the recent EA WFD data and revisiting SSSI condition assessments in light of this. But in the meantime, our latest advice on the geographical scope for mitigation for the New Forest can be summarised below:

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• Development draining to Beaulieu and Lymington river estuaries – Mitigation should be located within these river catchments as a first and preferred option. If it can be reasonably shown that mitigation cannot be delivered within these river catchments, it may be considered appropriate to locate mitigation in adjacent/nearby catchments – i.e. the wider New Forest southern coastal catchment, and/or the Western Yar and Newtown catchments on the Isle of Wight (please be aware that such cases should not be primarily based on cost effectiveness).

• Development draining to other New Forest catchments and sea outfalls draining to the Solent (including Avon Water, Danes Stream, Dark Water and Sowley Stream, and Pennington STW) – Mitigation would be appropriate in the wider New Forest southern coastal catchment (including Beaulieu and Lymington rivers), and/or the Western Yar and Newtown catchments on the Isle of Wight.

This letter represents Natural England’s latest advice to the National Park Authority for you to consider as ‘competent authority’ in the delivery of your planning functions. Natural England will continue to keep your authority updated as work on nutrient neutrality within the Solent catchment progresses.

If you have any queries at all do let me know.

Yours faithfully

Becky Aziz
Senior Advisor Sustainable Development
Thames Solent Area Team
Natural England
020 8026 0064 / 07787005505