In a low peat area, it is essential to keep water levels stable – and at least high enough – throughout the year. “Ideally, the water height is the same as the ‘cutting table’ height, which is the height at which we mow,” Toon explains. “However, due to increasing drought, the water level is falling too much. In theory, De Zegge should be fed with groundwater, but it is literally being pulled away from the bottom due to dewatering of the surrounding areas. At that time, there is a solution – temporary and less “Ideal – to allow surface water to flow from outside our nature reserve.”
However, in terms of nutrients, these external surface waters do not meet the requirements of the lowland peat area. “The water flowing from the surrounding areas is full of nutrients such as sulphates, nitrates and phosphates,” says scientist Willem-Jan Emsens from Antwerp Zoo’s Research and Conservation Center (CRC). Toon agrees: “It may seem contradictory, but we don’t want that. This ‘rich water’ is the ‘dirty water’ of the layered peat area because of the nutrients present. This is not compatible with the ‘oligotrophic’, ‘poor’ habitat.” De Zegge If we bring this poor habitat into contact with “rich water”, this habitat will also become “richer” and a change will occur in terms of fauna and flora and for De Zegge to perform its natural ecosystem functions, among other things, detention carbon dioxide, we must strive to achieve the natural state of the low peat area as much as possible.
The word helophyte contains the Greek word “helos,” which means “swamp.” “The term ‘helophyte’ is a collective name for marsh plants that root underwater and grow above water, such as reeds or cattails. This type of plant does all the work in the helophyte filter,” Toon explains. “In a 100-200 meter long channel, Rich, nutrient-packed water flows through the plants’ roots, which extract all the nutrients. At the end of the path, the water comes out of the filter poorer – with fewer nutrients.”
What makes this Helovit filter so special is that in addition to this botanical filter system, there is also a harmless chemical component. “With the help of the water company Pidpa, we add cassettes to the Helovit filter containing IOCS granules. The ‘iron oxide coated sand’ granules will chemically bond with the phosphate in the water,” explains Willem Jahn. “This allows you to remove the phosphate along with the iron granules. This means fewer nutrients remain in the water that eventually flows into De Zegge.
The air plant filter is a temporary solution in De Zegge’s quest to rehumidify the nature reserve as much as possible. “We are collaborating with various partners to improve the quality of the incoming water. This heliophyte filter is part of the European ADMIRE project that will last for two years. The Antwerp Zoo Foundation (AZF) manages the area and maintains the vegetable filter. Staff cut the plants so they grow again and again. This way The filtering process can be repeated over and over again. The iron granules can become saturated, depending on the phosphate levels, but can also be removed and replenished. Pidpa takes care of the filter output and design by researchers from the Antwerp Zoo Science Center, ZOO Planckendael and the Antwerp Zoo Research and Conservation Center (CRC). They ensure the filter effect is monitored.
It’s a sustainable filter, but an air plant filter is only an intermediate step on the road to a more sustainable solution. “The current situation does not guarantee long-term recovery, even with the Heliophyte filter. If we want to achieve this, we must aim to restore the hydrological ecosystem on a landscape scale. Until then, the Heliophyte filter is a technical aid during droughts.”
