Why does Aalborg Utility measure nitrate?
At Aalborg Utility they would like to secure the drinking water supply for the future so that citizens can continue to get clean drinking water from their taps.
One problem, however, is that the large discharge of fertilizer on the fields in the past has meant that the excess, unconsumed nutrients in the form of nitrate have, over the years, moved down through the soil layers, through the lime subsoil and further via cracks and fissures into the groundwater and thereby to the drinking water boreholes.
The problem in the Aalborg area with nitrate in the groundwater is generally quite complex, as the geological conditions around Aalborg mean that you do not have natural protection against excess nitrate, as you have in other parts of the country. There is simply a lack of nitrate reduction capacity in the soil layers.
Furthermore, the long residence time of the water in the unsaturated lime zone means that you are only now seeing the effect of the large nitrate surpluses that were discharged in the 70s and 80s.