Nutrient neutrality helps to balance the needs of the environment, society, and the economy by making new developments more sustainable and preventing further damage to important habitat sites.
The construction of new homes and other accommodation developments is vital for both society and the economy – but doing so sustainably has become increasingly important. There are a number of human activities that contribute to the increase in nutrients, but nutrient neutrality focuses on the impact of urban development – particularly “over-night developments” (residential housing, visitor accommodation, student accommodation and care homes).
“Over-night developments” add nutrients to the environment throughout the development’s life – from construction, to habitation, to their end of use. This can come from the land conversion, urban runoff, and through the increased amount of sewage going to waste water treatment works (WwTW) (Figure 1). WwTWs are required to remove nutrients in-line with their permits, but some nutrients are still released into the environment as it is not technically achievable to completely remove them. Increased demand on a WwTW means more water is passing through the systems and more nutrients are released into the environment.
Natural England has produced a detailed methodology and calculator setting out how nutrient neutral development can be achieved. The calculator can be used to find out the current and the future nutrient loading of a development site, and calculate the amount of mitigation needed to offset any increase in nutrients. Many aspects of a site are taken into consideration, including soil drainage type, annual rainfall, and which WwTW it is served by. To secure planning permission, developments now need to show that any increased nutrient loading is mitigated.
Nutrient mitigation can come in many forms, for example: creation or restoration of semi-natural habitats, treatment wetlands, retrofitting Sustainable Drainage Systems (SuDS), upgrading old package treatment plants and septic tanks, developing new WwTWs or temporary agricultural management (short term only). A developer could make their own mitigation, but as it is costly and time consuming process, it is usually more feasible to buy credits from an existing nutrient mitigation scheme or use a mix of on-site measures and purchased credits. Our Partnership has produced a list of available mitigation schemes.