This report comprises Part 1 of a series of reports on nutrients.
This report provides the outputs from a literature review on catchment management Nature-based Solutions (NbS) in order to identify whether there are solutions that have a sufficient evidence base to:
a) support the scientific principles that show a solution will deliver nutrient mitigation, and
b) determine whether each studied measure can have a percentage nutrient removal estimate derived from the literature, as this will support the deployment of measures by allowing quantification of what they will deliver before they have been deployed.
The review has also identified knowledge gaps in the literature that should be considered in order to assist with recommending NbS for nutrient mitigation. Additional to the review of NbS for nutrient mitigation, this review has also assessed whether there is a sufficient evidence base to support habitat-specific nutrient export coefficients for use in determining the background nutrient export that will remain following agricultural land use conversion mitigation schemes.
To align the outputs from this review with the outputs from nutrient budgets for new developments, which show an amount of N or P that needs mitigating in kg/yr, literature was reviewed to determine if it is possible to derive estimates of the percentage efficiency of different NbS for nutrient mitigation. If robust percentage efficiencies for mitigation effectiveness can be derived, they can be applied to estimates of nutrient loads entering a mitigation solution to provide an estimate of load reduction (in kg/yr) that a mitigation solution can support.
It is known that the efficiency of NbS for nutrient mitigation is influenced by different environmental and design factors. Thus, the literature has aimed to answer the following two research questions:
1. Can robust estimates be derived for the percentage efficiency of N and P removal for different types of NbS related to nutrient mitigation?
2. What key factors influence the percentage efficiency of nutrient removal for a given type of NbS?