Blue Nitrogen: A Nature-Based Solution in the Blue Economy as a Tool to Manage Terrestrial Nutrient Neutrality.

There is growing concern about the impact of rising nutrient loading on aquatic ecosystems and on human health, due to increased urbanisation and associated sewage effluents. This has led to a policy focus on land-use change or agricultural practice change as nutrient mitigation strategies, but these fail to consider the ultimate downstream receiving environments such as marine ecosystems. Within the UK there has been increasing recognition that housing density in certain sensitive locations is impacting the conservation status of marine features, through the increase in nutrient loading to the marine environment. In order to comply with the statutory obligations to protect these marine features, the competent authorities have required developers to mitigate the impact of these additional nutrients. Current approaches include converting agricultural land to woodland and wetland habitats that release less nitrogen than the agricultural land they replace. This difference is used to offset the nutrient loading from the new development, but such a terrestrial-focused catchment-based mass balance approach has a number of limitations. Current solutions for nutrient neutrality in the UK take a narrow land-focused approach that fails to acknowledge the potential contribution of the marine environments to mitigate nutrient enrichment. We propose that marine nature-based solutions offer an economically and ecologically viable alternative to terrestrial schemes, that can reduce the nitrogen loading to the marine environment, increase ecosystem service provision and increase biodiversity