3rd sampling campaign on the Yvel basin

Thursday, June 20, 2019, a mixed team made up of CNRS researchers and technicians from the Brittany Chamber of Agriculture continued its work of identifying the contributing areas of Phosphore in the Yvel basin. Under assumptions, lowland wetlands (grass strips and cultivated soils) may be among the most water-contributing areas of the basin to Phosphorus. This work is a prerequisite for the definition of Payments for Ecosystem Services that will be offered to farmers.

Soils from about ten wetland stations (areas of the basin where the water table occasionally rises to the soil surface) were removed. As in the two previous seasons, sampling covered all the constituent parts of these areas (permanent meadows, grass strips and cultivated areas) in order to:

  • determine the characteristics of the soil from the point of view of its capacity to store the Phosphorus and to release it in solution during the ascent of the aquifer. For that, it will be necessary:
    • bring the samples back to the laboratory,
    • measure their maximum Phosphorus absorption capacity (are the soils able to act as a filter between the plots, the watercourse and the lake water?)
    • measure their current rate of Phosphorus saturation and the theoretical capacity of the soils to release Phosphorus in solution (therefore in the water table and the watercourse)
  • identify the determinants of these characteristics and properties by collecting all information on agricultural practices within these areas:
    • what are the inputs of phosphorus into the soil related to the inputs of organic or mineral fertilizers?
    • have the doses delivered been stable or decreased?
    • does tillage lead to deep burial of the phosphorus, or does it maintain phosphorus on the surface?
    • how long have the grass strips been implanted?

What do we do with soil samples once collected?

After drying for 2 or 3 weeks, then sieving, some of the collected soil will be sent to the INRA laboratory in Arras for analysis. Another part will be used for laboratory experiments aimed at characterizing soil properties vis-à-vis the phosphorus.

What interpretation of the results?

The results of this third sampling campaign, coupled with those of the two previous campaigns will allow researchers to make recommendations to farmers to limit the risk of Phosphorus leakage from these areas of the watershed, and ultimately reduce exports from agricultural Phosphorus to Lac au Duc. It will be recalled that the emissions of Phosphore agricole represent 90% of the total Phosphorus entering the lake each year, and that this Phosphorus is directly at the origin of the development of cyanobacteria and with very negative impacts on the local economy (camping, nautical activities, fishing, hotels, drinking water, etc.).

In the end, the results obtained will provide references to farmers and managers of the Yvel basin allowing improved management of wetlands from the point of view of the Phosphorus, seeking to reconcile water quality protection and agronomic valorisation.They They will also be able to scale and offer Payments for Ecosystem Services to farmers, one of whose ultimate goals is to help farmers make the changes in practices needed to reduce leaks from Phosphorus to the Lake.