With more than 60% of the land farmed, with vulnerable freshwater and marine environments, and with one of the most intensive, export-oriented livestock sectors in the world, the nitrogen (N) pollution pressure from Danish agriculture is severe. Consequently, a series of policy action plans have been implemented since the mid 1980s with significant effects on the surplus, efficiency and environmental loadings of N. This paper reviews the policies and actions taken and their ability to mitigate effects of reactive N (N r ) while maintaining agricultural production. In summary, the average N-surplus has been reduced from approximately 170 kg N ha −1 yr −1 to below 100 kg N ha −1 yr −1 during the past 30 yrs, while the overall N-efficiency for the agricultural sector (crop + livestock farming) has increased from around 20-30% to 40-45%, the N-leaching from the field root zone has been halved, and N losses to the aquatic and atmospheric environment have been significantly reduced. This has been achieved through a combination of approaches and measures (ranging from command and control legislation, over market-based regulation and governmental expenditure to information and voluntary action), with specific measures addressing the whole N cascade, in order to improve the quality of ground-and surface waters, and to reduce the deposition to terrestrial natural ecosystems. However, there is still a major challenge in complying with the EU Water Framework and Habitats Directives, calling for Environmental Research Letters Environ.

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Considerable specific cross-sectional and review studies have linked exposure to green spaces to improving public health, but there is no bibliometric review attempting to systemically and retrospectively analyze these existing articles. Here we aim to uncover global research status, trends, and future prospects in green spaces and health (G-H) research then propose a framework for the underlying mechanisms and pathways that link green space to public health. We obtained 18 961 G-H research publications from the core Web of Science collection from 1901 to 2019, analyzing the characteristics of publication outputs, key scientific disciplines, and differences in performance between countries and institutions. Besides, content analysis was conducted to analyze the keywords, including keyword co-occurrence analysis and keyword clustering analysis. We found: (1) a steady quantitative increase in publications, active journals, and involved countries and institutions since the 1990s; (2) a significant increase and changes in G-H related interdisciplinary categories, with environment-related disciplines becoming the mainstream; (3) research focus and trends that were identified based on the analysis of high-frequency co-occurring keywords; (4) three main knowledge domains, namely, green spaces and physical health, mental health, and ecosystem health, that were identified and visualized based on keyword clustering analysis; (5) a framework of underlying mechanisms and pathways linking green space to public health that is proposed based on visualization of the three main knowledge domains. We suggest that the main challenge of G-H research is to further clarify in-depth the underlying mechanisms and pathways from multiple perspectives, including multiple nations, disciplines, and study designs. The lack of co-occurring keywords and clustering information related to social well-being suggests that research related to 'social health' is lacking. Based on a clear understanding of the quantity, quality, and characteristics of green space for public health, a health-based environmental plan should be proposed in the future.