Nitrogen (N) and phosphorus (P) are nutrients essential for plant growth, but too much nutrient in runoff from land into waterbodies can cause excessive plant and algae growth (‘eutrophication’). Phosphorus is the most important nutrient in freshwater systems.
This biological response can then result in dramatic reductions in oxygen concentrations in the water causing damaging effects to fish populations and other water life, with a detrimental knock-on effect on birds and other species that depend on them as a food source. Many waterbodies are protected as designated sites (or habitats sites) and managed by Natural England.
Eutrophication is likely to get worse in future years as Environment Agency (EA) research from 2016 suggests climate change is likely to increase nutrient concentrations in England’s rivers – particularly Phosphorus during low flow periods in summer.
Government agencies (EA, Natural England, DEFRA) are working with stakeholders to improve wastewater treatment (e.g., a reduction to 0.5 mg/l Phosphorus in consented ‘point source’ discharges from Wastewater Treatment Works by 2024) and so improve the Water Framework Directive (WFD) status for Phosphorus of the affected waterbodies. However, EA modelling suggests that these improvements alone are not sufficient to produce good Phosphorus status at all the investigated sites, and so further intervention is necessary, for example reducing inputs of Phosphorus from ‘diffuse sources’ such as agricultural land and residential development.
New provisions under the Environment Act 2021 have increased Natural England’s requirements to achieve nutrient neutrality from seven catchment areas across 31 Local Authorities, to 27 catchment areas across 42 Local Authorities. Nutrient neutrality is a means of ensuring that a plan or project does not add to existing nutrient burdens so there is no net increase in nutrients at a habitats site because of the plan or project (i.e., it “consumes its own smoke”). When nutrient neutrality is properly applied and the existing land use does not undermine the conservation objectives, Natural England consider that the scheme would be deliverable in accordance with the Habitats Regulations, would pass the required Appropriate Assessment and so an adverse effect on integrity alone and in combination can be ruled out.
Where neutrality measures are needed, their aim is to avoid impacts to habitats sites, rather than compensating for impacts once they have occurred.
The new provisions are supported by Natural England Guidance issued in March 2022 and by a ‘Nutrient Neutrality Generic methodology’ issued in February 2022.
Where a development cannot achieve nutrient neutrality, then some form of mitigation is required. This requires offsetting the Nitrogen and Phosphorus produced by wastewater and surface water from the proposed development. The potential solutions are:
- Reduce Nitrogen and Phosphorus by an equivalent amount from land in the same ownership elsewhere in the same catchment. For example, reduce the amount of Nitrogen and Phosphorus fertiliser applied to an agreed area of land elsewhere under arable cereals by permanently changing the land use to grazing, wildflower meadows, or to forestry requiring lower or no nutrient inputs.
- Find a third-party landowner willing to provide the land use offsetting in (1) for an annual fee in the form of a nutrient credit.
- Obtain nutrient credits from a low- nutrient developer changing the land use elsewhere in the catchment, such as Forestry England developing commercial woodlands.
- Provide treatment wetlands to remove nutrient from watercourses flowing through the landholder’s property or from surface water runoff from the proposed development.
- Find an existing nutrient offsetting scheme within the catchment that has unused mitigation capacity.
If none of these mitigations are possible then the proposed development cannot go ahead. There are many permitted residential and commercial developments throughout England that are currently on hold awaiting assessment, and large areas of allocated land (particularly ‘brownfield’ sites) that may be undevelopable as the amount of land required for nutrient offsetting is in many cases greater than the development land area itself.
In summary there are clearly significant conflicting issues that should be exercising government around a policy that puts wildlife and water quality improvement before food production and before houses for people to live in. A return to water catchment- based development policies including cross boundary local authority consultation is urgently required.
Dr Paul Hardwick,
Technical Director Water Sciences,