S2: Chaban-Delmas (Gironde, FR)

Site “S-2”, Location: Chaban-Delmas 44°51.322′ N, 000°33.119′ W

Brief description:

This former urban wasteland is part of the Parc aux Angéliques, which borders the right bank of the Garonne, providing rest areas and increasing biodiversity and connectivity (green corridor). The soil developed above the embankments has a sandy texture, marked by the legacy of former industrial and port activities.

Phytomanagement uses the combination of various plants and micro-organisms, assisted if necessary by soil amendment, to produce valuable or ecologically interesting biomass, to progressively reduce exposure to contaminants and to improve the ecological functions of the soil and the underlying ecosystem services. It is a less invasive and less costly remediation option than excavation and landfill, more environmentally friendly and integrated into the bioeconomy.

The phytomanagement systems evaluated at this site by the Phy2SUDOE project are forest plantations (e.g. black poplar), perennial grasses (e.g. ryegrass, fescue, oats) associated with legumes (e.g. alfalfa). Soil amendments tested have been compost and biochar. Alfalfa has produced a healthy vegetation cover, without exposure of herbivores and insects to pollutants, which diversifies over time (from 36 to 72 plant species depending on season and area). It prevents dust from being blown away by the wind and favours the biodegradation of organic compounds.

The structural and functional diversity of plant and soil microbial communities is assessed. The diversity of soil mesofauna is also studied. In 2020, 2 trials were set up to study the evolution of the plant community and the increase in biomass under the influence of organic amendments (compost combined or not with biochar) or foliar fertilisation.

Actions during the phy2SUDOE project

Monitoring actions

  • Plant biomass in the plots: annual cuttings in late spring and autumn.
  • Crushing and analysis of the plants.
  • Leaf area index measurements.
  • Drone imagery.
  • Monitoring of extractable metals in the soil.
  • Monitoring of insects on the soil surface.

Maintenance actions

  • Irrigation: depending on climatic conditions (summer drought).
  • Pruning and replanting of trees.
  • Fence maintenance.