The effect of groundwater extraction on nitrate vulnerable recharge areas (NFI) in Denmark. MIKE SHE simulations of different extraction scenarios.

Abstract: This thesis aims to outline the effect of different abstraction scenarios on the extent of nitrate vulnerable recharge area (NFI) in two study areas in Denmark. NFI were designated in order to protect vulnerable groundwater resources from nitrate pollution, where the geology overlying the aquifers does not serve as a sufficient barrier. NFI are officialy calculated by taking into consideration the recharge area at the permitted abstraction rates of the waterworks, however those rates are often much higher than their actual abstraction. Two existing MIKE SHE groundwater models were chosen and several abstraction scenarios were simulated to compare the extents of groundwater recharge areas they yield. The studied areas were Halsnæs and Brokilde in the north of the island of Sjælland. The results of the simulations especially in Brokilde show a significant difference in NFI of 81 ha between the actual and the permitted scenario. Also scenarios in between the actual and the permitted abstraction were simulated, those follow the trend clearly. The results in Halsnæs were not that sharp, since the observed wells were not concentrated in one place as in Brokilde and abstraction rates were significantly lower. The decrease of NFI for the actual abstraction rates can be of particular interest for municipalities, since the designation of NFI results in costs for reimbursing farmers for their effort to use less nitrate for example. In order to apply the results of this thesis to other areas, further investigation and the simulation of more abstraction scenarios are required.