1 Integrated Geographical and Social Studies, Faculty of Agricultural Sciences, Aarhus University, Aarhus University2 Institute of Biostatistics, Faculty of Health Sciences, Aarhus University, Aarhus University3 Department of Agroecology and Environment, Faculty of Agricultural Sciences, Aarhus University, Aarhus University4 GEUS5 Department of Agroecology - Agricultural Systems and Sustainability, Department of Agroecology, Science and Technology, Aarhus University6 Department of Public Health - Department of Biostatistics, Department of Public Health, Health, Aarhus University7 Department of Agroecology - Agricultural Systems and Sustainability, Department of Agroecology, Science and Technology, Aarhus University8 Department of Public Health - Department of Biostatistics, Department of Public Health, Health, Aarhus University
This presentation assesses the long-term development in the oxic groundwater nitrate concentration and nitrogen (N) loss due to intensive farming in Denmark. Firstly, up to 20-year time-series from the national groundwater monitoring network enable a statistically systematic analysis of distribution, trends and trend reversals in the groundwater nitrate concentration. Secondly, knowledge about the N surplus in Danish agriculture since 1950 is used as an indicator of the potential loss of N. Thirdly, groundwater recharge CFC (Chlorofluorocarbon) age determination allows linking of the first two dataset. The development in the nitrate concentration of oxic groundwater clearly mirrors the development in the national agricultural N surplus, and a corresponding trend reversal is found in groundwater (see Figure 1). Regulation and technical improvements in the intensive farming in Denmark have succeeded in decreasing the N surplus by 40% since the mid 1980s while at the same time maintaining crop yields and increasing the animal production of especially pigs. Trend analyses prove that the youngest (0-15 years old) oxic groundwater shows more pronounced significant downward nitrate trends (44%) than the oldest (25-50 years old) oxic groundwater (9%). This amounts to clear evidence of the effect of reduced nitrate leaching on groundwater nitrate concentrations in Denmark.