The well field of Holten is located in an area with vulnerable sandy soils.

The travel times vary within the capture zone.
The abstraction has high nitrate concentrations, mainly due to the agricultural land use (pasture, arable land, and since 1970 maize).
The yearly averaged values of nitrate concentrations in the groundwater recharge for these land uses have varied due to intensification of the agriculture and in atmospheric nitrogen deposition.
A land use scenario is tested for its effect on the nitrate concentration in the abstracted water. Pasture is converted to nature in a zone East of the abstraction in 2014.
The resulting development of the nitrate concentrations have been calculated using WellGrapher. Retardation and decay have been neglected.

The land-use change would reach the abstraction with a delay of 10 years due to the travel times in the subsurface.