How does desiccation work?
Human intervention
Desiccation is primarily caused by changes made to the water system in order to meet the requirements of land use. We make a distinction between three kinds of factors (Beugelink et al., 1995):
- Dewatering and faster drainage for agriculture and horticulture cause approximately 60% of desiccation in the Netherlands.
- Groundwater abstraction for drinking and industrial water and irrigation cause approximately 30% of desiccation.
- Other causes, such as the increase in the metalled surface area, afforestation and sand winning account for approximately 10%.
How do the activities described here result in the desiccation of ecosystems?
They lead to changes in the water system such as:
- lowering of the water table;
- reduced upward seepage;
- the introduction of water from outside the system.
Desiccation in the High Netherlands
In the High Netherlands, desiccation is usually the result of a low water table. In the transitional areas from the High to the Low Netherlands, upward seepage is generally too low, so that the supply of calcium-rich groundwater is affected, sometimes severely. The long residence time below the surface (sometimes in excess of 100 years) means that certain substances, such as calcium and iron, are absorbed in the water from the sand strata through which the water flows. Where this water seeps through at ground level, highly specific conditions are therefore created, with types of plants characteristic for those conditions. If seepage is interrupted, these plant communities are subjected to severe pressure. An increase in groundwater extraction and faster drainage can prevent water from reaching the ground level, thereby making seepage impossible.
Desiccation in the Low Netherlands
In the lower, Western, part of the Netherlands, with the exception of the dunes, the fall in the water table is a minor factor in desiccation. Here, the introduction of water from outside the system to control water quality is the main cause. This is a result of, for example, upwelling saltwater (salinisation).
In the dunes, the problem is the fall in the water table cause by drinking-water extraction and the pretreated water introduced from the Rhine and the IJsselmeer to compensate.
