15.3.2.2 Moksloot Valley, Island of Texel (Wadden Sea)
The Moksloot valley is situated in the southwestern part of Texel. In 1993 the
drinking water company decided to terminate the abstraction of groundwater in the
Moksloot area, mainly because an adjoining camping site had polluted the well
areas, because of leaking septic tanks. The nature conservation organization in
charge of management of the dune valleys decided to implement sod cutting in a
number of dune valleys in order to remove the eutrophic top soil and reset succession. In the autumn of 1993, about 100 ha of dune slack area underwent sod
cutting. The vegetation development has been monitored since then. Groundwater
levels increased after the termination of drinking water abstraction. Owing to
increased groundwater discharge the pH also increased (Grootjans et al. 2001). We
will discuss the results of restoration in two types of dunes slacks:
1. A surface water slack that receives both groundwater and surface water from
upstream areas and which as a consequence has become a nesting place for
numerous birds.
2. A groundwater-fed slack that only receives groundwater from an adjoining
dune area and from precipitation water.
The monitoring results are shown in Fig. 15.4. During the first 5 years there
was almost no difference in vegetation development, except that the total species
richness in the surface water slack was higher than in the groundwater slack
(Grootjans et al. 2001). After 5 years the calciphilous pioneer species increased
considerably in the groundwater-fed slack, while in the surface water slack the
eutrophic grassland and marsh species increased at the cost of the nutrient-poor
pioneer species.
In the groundwater-fed slack the re-establishment of calciphilous target species
was very slow, but stabilized after 10 years, while in the surface water slack
development of the target community was fast, but it did not last long. These
different responses after rewetting clearly show that rewetting with groundwater is
more successful for the development of a typical dune slack community than
rewetting with surface water. The latter type of water mobilizes nutrients from the
organic matter, while iron-rich groundwater reduces the availability of phosphorous in the soil (Lamers et al. 2002). Furthermore, the large areas of surface water
attracted many water birds, which increased the availability of nutrients
considerably.
15.3.2.3 Meinderswaal Valley (Goeree, Holland Coast)
The third restoration project was carried out in a dune area that is also used for the
production of drinking water. With the development of new techniques for this
process for the large cities, parts of the dunes were no longer needed; thus, many
246
A. P. Grootjans et al.
The Moksloot valley is situated in the southwestern part of Texel. In 1993 the
drinking water company decided to terminate the abstraction of groundwater in the
Moksloot area, mainly because an adjoining camping site had polluted the well
areas, because of leaking septic tanks. The nature conservation organization in
charge of management of the dune valleys decided to implement sod cutting in a
number of dune valleys in order to remove the eutrophic top soil and reset succession. In the autumn of 1993, about 100 ha of dune slack area underwent sod
cutting. The vegetation development has been monitored since then. Groundwater
levels increased after the termination of drinking water abstraction. Owing to
increased groundwater discharge the pH also increased (Grootjans et al. 2001). We
will discuss the results of restoration in two types of dunes slacks:
1. A surface water slack that receives both groundwater and surface water from
upstream areas and which as a consequence has become a nesting place for
numerous birds.
2. A groundwater-fed slack that only receives groundwater from an adjoining
dune area and from precipitation water.
The monitoring results are shown in Fig. 15.4. During the first 5 years there
was almost no difference in vegetation development, except that the total species
richness in the surface water slack was higher than in the groundwater slack
(Grootjans et al. 2001). After 5 years the calciphilous pioneer species increased
considerably in the groundwater-fed slack, while in the surface water slack the
eutrophic grassland and marsh species increased at the cost of the nutrient-poor
pioneer species.
In the groundwater-fed slack the re-establishment of calciphilous target species
was very slow, but stabilized after 10 years, while in the surface water slack
development of the target community was fast, but it did not last long. These
different responses after rewetting clearly show that rewetting with groundwater is
more successful for the development of a typical dune slack community than
rewetting with surface water. The latter type of water mobilizes nutrients from the
organic matter, while iron-rich groundwater reduces the availability of phosphorous in the soil (Lamers et al. 2002). Furthermore, the large areas of surface water
attracted many water birds, which increased the availability of nutrients
considerably.
15.3.2.3 Meinderswaal Valley (Goeree, Holland Coast)
The third restoration project was carried out in a dune area that is also used for the
production of drinking water. With the development of new techniques for this
process for the large cities, parts of the dunes were no longer needed; thus, many
246
A. P. Grootjans et al.