Technosol composition affects Lumbricus terrestris surface cast composition and production
Résumé
Constructed Technosols deliberately combine technogenic materials to obtain specific services (e.g. plant biomass production) in particular contexts (e.g. industrial wasteland reclamation). Their ecological reclamation by key members of the soil fauna, such as earthworms, is a promising way to ensure such services. However, literature which treats these animals as a biological agent of constructed Technosol functioning is very scarce. This work assesses the effects of the composition of a constructed Technosol (i.e. the proportions of the constituent materials) on earthworm (Lumbricus terrestris) surface cast production and composition, and to a lesser extent on earthworm survival and biomass. Earthworms were placed in laboratory microcosms made of different proportions of materials: green-waste compost (GWC) and thermally treated industrial soil mixed with paper mill sludge (TIS/PS), for 30 days. We found that 25% of GWC on the surface and 75% of TIS/PS below was the most beneficial composition in that it gave the highest body mass gain. Furthermore, this composition generated a moderate surface cast production compared to other compositions and an increase in microorganism activity and number compared to non-ingested by earthworm soil. This composition also led to casts with bacteria of diverse morphologies and largest microaggregates compared to compositions without GWC, resulting from the ingestion and mixing of the two materials in the earthworm gut. However, earthworms did not modify the carbon contents of surface casts. This laboratory approach was a necessary step before field assessment of ecological reclamation by earthworms. From a soil engineering point of view, this contributes to better-managed soil construction for ecological reclamation.