Trend reversal of nitrate in Danish groundwater--a reflection of agricultural practices and nitrogen surpluses since 1950.
This paper assesses the long-term development in the oxic groundwater nitrate concentration and nitrogen (N) loss due to intensive farming in Denmark. First, 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. Second, knowledge about the N surplus in Danish agriculture since 1950 is used as an indicator of the potential loss of N. Third, groundwater recharge CFC (chlorofluorocarbon) age determination allows linking of the first two data sets. 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. 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.
Geological Survey of Denmark and Greenland (GEUS), Department of Quaternary and Groundwater Mapping, DK-8270 Højbjerg, Denmark. bgh@geus.dk
Birgitte
B
Hansen
Laerke
L
Thorling
Tommy
T
Dalgaard
Mogens
M
Erlandsen
D000383:Agriculture / Q000379:methods*; D003718:Denmark; D004784:Environmental Monitoring; D058735:Environmental Policy; D005618:Fresh Water / Q000737:chemistry*; D009566:Nitrates / Q000032:analysis*; D058458:Nitrogen Cycle; D013995:Time; D014874:Water Pollutants, Chemical / Q000032:analysis*; D014877:Water Pollution, Chemical / Q000706:statistics & numerical data*; D014881:Water Supply / Q000032:analysis / Q000706:statistics & numerical data
D009566:Nitrates; D014874:Water Pollutants, Chemical