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).
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.
Overnight development adds 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). WwTWs are required to remove set amounts of nutrients, meaning some nutrients are still released into the environment. More demand on the WwTW, mean more nutrients are flushed into the environment.
Natural England has created a calculator that can be used find out the current and the future nutrient loading of the site, and uses those figures to calculate how much mitigation is 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 get planning permission, developments now need to show that any increased nutrient loading is mitigated. More detail on how the calculator works and the calculator can be found here.
Nutrient mitigation can come in many forms. It could be achieved through the creation or restoration of semi natural habitats, the creation of treatment wetlands, retrofitting Sustainable Urban Drainage Systems (SUDs), making improvements to PTPs and septic tanks, developing new WwTW or temporary agricultural management (short term only). A developer could make their own mitigation, but as it is costly and time consuming, it is usually more feasible to buy “credits” from a nutrient scheme owner – someone who has already developed a business specifically to sell credits – or use a mix of on-site mitigation and purchased credits. A list of available mitigation schemes can be found here.