At the heart of Grenspark Kalmthoutse heide is the Groote Meer, one of the Netherlands' largest fens. Due to water inflow from agriculture, the water quality is deteriorating. To turn the tide, a filter of iron sand is being constructed on a large scale for the first time in the world. An innovative project under the European funding programme LIFE and the LIFE HELVEX project.
The Groote Meer has an enormous attraction for special plants and animals that hardly get a chance elsewhere in Europe, such as shore weed, belted grebes (photo) and the eared grebe. However, there is a problem; water quality has been deteriorating for decades. Rare plants grow in a clean environment with nutrient-poor sand and clear water. Too much fertiliser increases algal growth and species such as reed and cattail.
Water supply
Time to turn the tide. That's why Natuurmonumenten started looking for a way to improve or at least stabilise the water quality of the Groote Meer. "The water and the bottom of the fen are now getting far too many nutrients. This is disastrous for a nature reserve like De Groote Meer," says project leader Robert Stoop. Much of the water supply of De Groote Meer comes from the agricultural area De Steertse Heide, just across the border on Belgian territory.
For years, promising methods to at least stabilise the water quality of the Groote Meer have been investigated. The project team consisted of the partners that Natuurmonumenten works with more often such as the Grenspark Kalmthoutse Heide, Waterschap Brabantse Delta, province of Noord-Brabant and Evides. Royal Haskoning advised on the possibilities at that stage. Last year, contractor Harteman from Tiel was selected to further design and start realising the treatment work. "Everyone has made a real effort for the Groote Meer. Harteman works together with consultancy and engineering firm Arcadis. They helped us arrive at a feasible model of the water treatment plant."
Iron sand
The final choice was to purify the water with a filter made of iron sand. The water enters a reservoir, after which it gradually flows through the iron sand. Iron sand consists of sand coated with iron oxide and is a by-product of drinking water production. The phosphate in the surface water, which causes algae growth and makes the fen soil so nutrient-rich, binds to the iron sand in the treatment works. The rest of the water passes through the filter so that the water supply to the fen is directly purified. As a result, the Groote Meer is fed with water of a much better quality than at present.
Netherlands first
Arjon Buijert, Water Management specialist at Arcadis, is closely involved in the purification work now being installed at the Groote Meer. "There have been tests with a filter made of iron sand, but never on this scale. Worldwide, I know of no comparable project. The Netherlands is leading the way. It is also hugely relevant here because agriculture is so close to nature."
According to Buijert, this purification work is an example where you can very specifically help and protect natural areas. "Iron sand is a natural product. We recycle by using it now in the filter bed. So it is a relatively natural way of purification". But it is not infinitely sufficient. "Eventually, of course, the source has to change. That will happen in small steps. We estimate that the iron sand will last about a hundred years".
Temporary disruption on hiking and bridle paths!
On walking route Fuut and a bit on walking route Ree, as well as on some bridle paths around the Oude Meerbaan and behind the Groote Meer area, walkers and riders may encounter out-of-route truck traffic. Warning signs will be posted in the area to alert visitors.
Be careful, the works will last +/- 2 months.