During the NEW Harmonica consortium meeting in Hasselt the Flanders Environment Agency (VMM) organised a field trip within the Flemish Meuse catchment. The field trip went to the north of the Flemish province of Limburg.
This region, predominantly composed of sandy soils, is marked by livestock farming, grass and corn fields, and horticulture. Agriculture plays a significant role in the area’s water quality issues. Many actions by the agricultural sector over the past three decades have already improved water quality, although this improvement appears to have stagnated over the past 5 to 10 years.
The excursion was guided by Sander Palmans of the Provincial Research and Training Centre for agriculture (PVL) and Steve Meuris of the non-profit organization Boer en Natuur (Farmer and Nature). As local stakeholders, they collaborate with farmers in the region to implement measures aimed at improving nutrient water quality.
A constructed wetland in Bocholt
In this area, nitrate concentrations in surface water have consistently exceeded 50 mg nitrate/L, despite the implementation of successive action plans and regulations. In response to this, a project was initiated to explore the potential of constructed wetlands as an alternative to source-oriented measures for nitrate removal in a catchment. The initial challenge was to identify a suitable location for the wetland, a task made difficult by high land prices. However, one farmer agreed to provide a downstream area for this purpose, although the area was smaller than initially planned. The wetland, complete with controlled in- and outflows and planted with appropriate vegetation, was constructed last summer. An exceptionally wet winter resulted in immediate flooding of the wetland. Monitoring will now start to gain insights into the wetland’s potential for nitrate removal. The aim is to use the monitoring results to convince more farmers to allow the construction of wetlands on their land.
Controlled drainage and subirrigation in Bocholt
Drought is an increasingly important problem in this part of the Flemish Meuse catchment, a problem that has been highlighted by recent dry summers. Despite this, many fields in the area still maintain drainage systems that drain excess water during winter. A project is underway to guide farmers in transitioning from these existing drainage systems to a controlled drainage system. This system ensures fields are only drained for short periods when machinery needs access. For the remainder of the time, the drainage system remains closed, retaining water and nutrients within the field.
A unique situation was observed at the visited location where the field is situated below the water level of a nearby canal. In summer, the drainage system can be connected to the canal, allowing water from the canal to irrigate the field through the soil. This system of controlled drainage and subirrigation has clear effects on the field’s water management, providing clear benefits to farmers who agree to participate in the scheme. It may also have effects on water quality by retaining nutrients on the field during the winter and facilitating denitrification in the soil.
Bioreactor in Peer
At the third stop, another test involving an end-of-pipe solution was showcased. This stop was located near a monitoring point that is part of the Manure Action Plan (MAP) monitoring network. This network is managed by the Flemish administration to assess the impact of agriculture on the quality of surface and groundwater. A bioreactor filled with wood chips was installed in a ditch that flows from a biogas installation to the monitoring point. Due to denitrification, the nitrate concentrations in the outflow were 50% lower than those in the inflow. The results of this test are being used to promote the further installation of bioreactors in the area, although there are legislative hurdles to overcome.
