Introduction to desiccation theme
The Netherlands has got a lot drier in the last 50 years. This is the case despite the floods and near-floods in the area of the large rivers a few years ago, the occasionally excessive rainfall and the resulting regular flooding of the Westland area. The reduced availability of water, in particular as a result of the falling water table, has major implications for moisture-loving plants in the Netherlands.
What is desiccation?
The government defines desiccation as follows:
'A natural area is deemed to be desiccated if the available amount of groundwater of the right quality is inadequate to safeguard ecological values. A natural area is also deemed to be desiccated if water of a different quality has to be introduced to compensate for the lower water table or for reduced upward seepage of groundwater.' (Ministry of Transport and Public Works, 1994)
Desiccation is therefore linked by definition to the nature function and is a structural problem. Desiccation has nothing to do with inadequate rainfall. It is therefore inaccurate to describe a shortage of water for agriculture as desiccation. This is drought damage.
Causes of desiccation
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 types of cause (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%.
- lowering of the water table;
- reduced upward seepage;
- the introduction of water from outside the system.
- See How does desiccation work? for a more extensive discussion of these mechanisms.
Impact of desiccation
Desiccation threatens approximately 40% of native Dutch flora. These plants depend on the water table and/or specific groundwater upwelling conditions. Many of the characteristic plants of wet and moist environments in the Netherlands have already disappeared or face extinction. Some animal species are also threatened, such as insects that depend on specific plant species (that depend in turn on groundwater and/or groundwater upwelling) for reproductive purposes.
To compensate for the lowering of the water table, water authorities bring in water from elsewhere. This water is usually different in composition, and contains much more nutrients than the water naturally occurring in the area. This may lead to rank in the aquatic ecosystem. The main cause of this process is eutrophication. There is rank when tall, perennial forbs with leafy stems, such as blackberries, creeping thistles, reeds and water willow herbs grow and dominate.
- See illustration of the impact of desiccation (page is not available yet) for further information.
Developments in the desiccation policy
As far back as the 1970s (Grootjans, 1979; Gijsen, 1979; Beintema et al, 1979; Molenaar, 1980), conservation organisations reported that there were problems with the water table in the Netherlands. In 1985, the government responded to these signals for the first time. In the Second Policy Document on Water Management, the government noted that there was a considerable fall in the water table throughout the country compared to the situation in the 1950s (Ministry of Transport and Public Works, 1985). The scale of the problem was described in greater detail in the years that followed (Braat et al. 1987; Braat et al., 1989a; Braat et al., 1989b).
In 1990, desiccation was designated as one of the themes of the environment policy. The National Environmental Policy Plan (NEPP) (Ministry of Housing, Spatial Planning and the Environment, 1989) presented, as an objective for 2000, a 'standstill' compared to 1985. In other words, the area affected by desiccation had to be no larger in 2000 than in 1985.
During the debate on the NEPP, the Lower House voted in favour of the Lansink/Van Rijn-Vellekoop motion. The House asked the government to focus policy on reducing the area of desiccated land in the year 2000 by at least 25% compared to 1985. It should be pointed out that it was not known how large the desiccated area was in 1985. The motion of the Lower House was therefore primarily a political signal. Later, in the Water Evaluation Memorandum (Ministry of Transport and Public Works, 1994), the area for 1985 was set at the same level as the area for 1994, the first year of the full national survey.
The NEPP3 (Ministry of Housing, Spatial Planning and the Environment, 1997) states an objective for 2010. In 2010, the desiccated area fell by 40% compared to 1985.
Policy performance
In 2000, approximately 3% (15,000 ha) of the desiccated area had recovered fully in hydrological terms compared to 1985. The rate of recovery is therefore lagging a long way behind the target adopted by the Lower House. An evaluation has now been completed of the reasons for this disappointing performance (Vliet et al., 2002). The main conclusions are:
- The water and nature targets, as well as the criteria for recovery, are not clear and measurable enough; this hinders the implementation of the desiccation policy.
- Furthermore, the responsibilities of the numerous stakeholders (national government, provincial authorities, water boards and municipal authorities) are not clear. Coordination between the stakeholders is therefore difficult.
- The continuity of the financing instruments has been below par.
- The monitoring of the level of desiccation and of recovery from desiccation has been poorly managed so far.
- See also the indicators Desiccated areas in the Netherlands, 2000 and Recovery of desiccated areas, 2001.
- How to improve coordination, management and collaboration in anti-desiccation activities.
- How to set targets for anti-desiccation activities that are more operational and accountable.
- What action is required in the area of monitoring, reporting and evaluation and what agreements need to be made in this respect?
