Cleaning up agricultural water: an innovative pond brings together regional stakeholders

The Champigny aquifer in Seine-et-Marne provides drinking water to 1.5 million people. It is therefore essential that the quality of this resource is maintained. However, the aquifer lies in a particularly agricultural region where runoff and drainage water carry excess fertilizer and pesticides. Some of these pollutants inevitably end up in the groundwater. Ecological engineering measures have therefore been set up to collect runoff water before it reaches the catchment water and to degrade contaminants naturally. To achieve this, ingenious treatment ponds, designed by Irstea researchers, have been created at Rampillon: artificial wetland buffer zones (zones tampons humides artificielles – ZTHA). The effect of the sun, bacteria and plants combine to degrade pesticides and nitrates naturally. Nevertheless, these facilities must be combined with measures to decrease the use of such products, leading to changes in farming practices. Is it effective?

Rampillon: an innovative pond

The project was started in 2005 and brings together Irstea scientists, the main regional stakeholders and water managers. Since its construction in 2010, the Irstea team has been working on evaluating the effectiveness of the ZTHA, using equipment installed in 2012 (meteorological stations, flow monitors, probes, etc.) to achieve precise measurements. In 2014, this collective approach was recognized when the Environment Ministry awarded the project the National Environmental Engineering Prize, rewarding over 10 years of research and successive studies. The latest, funded by the Seine-Normandy Water Agency, finished in 2015, and the results were presented to the main project partners (Rampillon town council, river unions, water agencies and farmers) last February.

The project combines two complementary aims:

  • Reducing diffuse pollution at the source > adapting farming practices
  • Reducing transfers > intercepting water flows


The measures themselves reduce pollution by around 40% (the initial aim was 50%). “We have to remember that this is a natural system and, therefore, its effectiveness varies according to the seasons and years. In particular, results depend on climatic conditions,” notes Julien Tournebize, Irstea hydrologist and manager of the Rampillon pilot facility. For these reasons, the effectiveness of the ZTHA in reducing pesticide contamination varies from year to year, ranging from 55% to 25%. Nature is unpredictable. A further uncertainty is the variation in behavior – and therefore degradation – of the molecules (pesticides). Some respond better to the processes while others are resistant; researchers have been able to identify these and evaluate their different degradation rates.

The ZTHA can eliminate around 1.5 tons of nitrates, equivalent to only 10% of the yearly load. Although the ZTHA is too small to capture more, it still represents significant potential. In tandem, researchers have also investigated greenhouse gas emissions from the denitrification processes. A further positive is that results show no significant nitrous oxide emissions (with a heating capacity 300 times greater than that of CO2).

“Farmers have also been making a significant effort and the results are now being quantified: in 10 years (2005-2015), we saw a drop of 25% in average nitrate concentrations on entry,” notes Tournebize. Farmers are therefore making better use of their fertilizers.

These results have led to further questions regarding:

  • the transformation of pesticides
  • long-term capture of these molecules in sediment

Mobilizing catchment area stakeholders

Three farmers in the catchment area (355 hectares) participated in the project and managed 2 small ZTHAs set up before the main one (and monitored by scientists).“This helped them to take ownership of the process and implementation of wetland buffer zones,” notes Tournebize. “One of their fears when the project launched was that we would leave them with these facilities once the project ended. Our presence on the ground, to take readings several times a month, is therefore very important. We are in direct contact with them and they call us as soon as there’s a problem. They are our alarms!” Support also involves training: AQUI’Brie, a partner organization, led the way by providing farming advice (which molecules to choose, when to apply them, weeding strategies, etc.). As part of the Ecophyto ministerial plan, farmers invested in mechanical weeding equipment to reduce the use of fertilizers.

Regional stakeholders (Rampillon town council, Water Agency, etc.) also support the project enthusiastically. “Presenting the study results made it possible to answer many of their questions about the process and knowledge transfers. They are showing real interest in understanding how it all works, with questions such as ‘where do the nitrates go?’” explains Tournebize.

Scaling up

Interest in the Rampillon ZTHA goes beyond the limits of the local catchment area. Many visits to the facilities have been organized, attracting farmers, river technicians and water managers from across France. Visitors are curious to see what a wetland buffer zone looks like before launching similar measures in their own regions.

© Irstea © Irstea
In the field – March 2016 © Irstea

In order to help small communities add value to existing ZTHAs and to build more, a new project [1] has been launched in the region. The study area has been expanded and now includes the region of Nangis; it now covers an area of 132 km2 compared to the 3.5 km2 of the Rampillon catchment area. This is a significant change of scale and a new approach that combines the challenges of protecting water quality and maintaining biodiversity, creating a new regional dialogue.

Similarly, data collected from the Rampillon facility will be combined with data from a ZTHA in Indre-et-Loire to continue evaluating the performance of these measures [2]. The data from the 2 regions will subsequently be used to benchmark national implementation of the measures. The tools for this already exist and include a technical guide to implementing ZTHAs (Irstea) and role play to foster dialogue. The challenge now is to account for the complexity of the problems and test various solutions while collectively evaluating their socioeconomic and environmental impact on a regional scale. Fighting against diffuse agricultural pollution together!

[1] BRIE’eau Project (2016-2020) Combining water quality and biodiversity to build a new agricultural and ecological landscape in the Brie region. Supported by PSDR Ile-de-France. Scientific partners: IRSTEA, INRA, UPSud  Socioeconomic partners: AQUI’Brie, Biotope, Departmental Directorate (77), Chamber of Agriculture (77)

[2] 2016-2018, funded by Onema.