Grote Calie

The Winkelsbroek reserve encompasses approximately 24 hectares of important wetland complexes. It is part of the Natura 2000 protected Habitats Directive area, ‘Forest and heathland east of Antwerp’, which mainly consists of a beautiful mix of forests, heather landscapes and stream valleys. Many ponds were historically used for fishing or peat extraction. After years of nature management in Winkelsbroek, the area offers many opportunities for flora, fauna and recreation. 

The Grote Calie is historically contaminated by a former tannery located in Oud-Turnhout. Principally chromium (Cr) has been found in high concentrations in the soil and sediments of the stream. This metal exists as trivalent and hexavalent chromium. Hexavalent chromium is more soluble and therefore more easily taken up by plants and organisms than trivalent chromium. The dominant oxidation state of chromium depends on various environmental factors, such as the pH of the soil. 

Chromium contamination is primarily present in the sediments of the Calie, but it can also be expected in solid soil under the river, riparian soils and flooding areas. 

Several exploratory studies and sampling campaigns have already taken place, not only to estimate chromium concentrations, but also to assess their bioavailability and potential toxicity. 

We also monitor nutrient concentrations, like phosphorus. The concentrations detected to date can cause eutrophication and disturb certain types of soil and water flora and fauna. This is especially significant for the target habitats and species in Winkelsbroek. The origin of the nutrients still has to be investigated. Nutrients can enter the area via leaching of upstream agricultural lands or via the groundwater through seepage from nearby agricultural activity.

LIFE NARMENA applies phytostabilisation. This is a specific type of phytoremediation. Plants and their microorganisms stabilise and/or fix certain pollutants (metals) in the soil, rhizosphere or roots, instead of absorbing them. In the case of metal pollution, this will reduce the mobility of metals, reducing their bioavailability and consequently their effects on fauna and flora.If necessary, plant-associated bacteria are added, equipped with appropriate degradation mechanisms to help the plants survive in an environment of high levels of toxic substances such as metals. The plants are selected to be non-invasive in the environment in which they are applied and do not have a negative impact on the native flora and fauna. 

BAP will be applied on agricultural land and in the nature reserve. Each case will have specific requirements. 

The constructed wetland is an artificial swamp or flood zone, in which the water is purified by means of natural geochemical and biological processes. 

The constructed wetland consists of a sediment trap in the watercourse and a flood zone on the left bank of the Grote Calie. The flow slows down as soon as it enters the sediment trap. At this point the sludge has time to settle. The contamination is mainly bound to sludge particles and will therefore remain in the sediment trap. Especially at high flow rates, for example in winter or after heavy rain, the flood zone will be addressed. The vegetation that grows in the wetland will help to retain the contaminated sludge in its root zone. 

The constructed wetland will occupy one hectare and is ideally located just upstream of Winkelsbroek, in order to capture as much as metal pollution and nutrient as possible before the stream enters the nature reserve. 

Planning

The baseline monitoring of sediment, surface and groundwater and the soils of riverbanks and flooding area has been completed. A feasibility study on phytoremediation has also been carried out by the University of Hasselt. This includes feasibility screening of phytoremediation in the context of the Grote Calie, selection of the most appropriate phytoremediation mechanism (with a focus on phytostabilisation of chromium), identification of the most appropriate plants and bacteria and a thorough feasibility evaluation. Planting of the BAP vegetation has been completed and innoculation of the root zone is expected to take place in spring 2023. The works for the construction of the wetland have started in October 2022 and will be finshed before the winter. After, a post-intervention monitoring will be carried out.