Long-Term Nature-Based Solutions: Poplar Phytoremediation Effects on Soil Contamination and Soil Functionality

Soil degradation driven by long-term anthropogenic pressure affects up to 70% of European soils and poses major environmental and socio-economic risks. Nature-Based Solutions, particularly phytoremediation, have attracted attention as sustainable strategies for soil restoration. However, their long-term effects on soil functioning remain insufficiently understood. This study focuses on a contaminated site in northern France (Carrières-sous-Poissy, Île-de-France), where poplar (Populus sp.) plantations have been established as a phytoremediation measure. The site’s contamination is a result of extensive and long-term deposition of urban and industrial waste from the surrounding area, combined with the former use of improperly treated wastewater from the Paris region as fertilizer. The site includes two experimental fields with poplar plantations representing distinct stages of phytoremediation: a long-term stand installed 13 years ago, and a recently installed, one year old stand. The main objectives of this study are to 1) evaluate the contribution of poplar plantations to soil rehabilitation, 2) observe how contamination shapes key soil functions, and 3) assess the robustness of selected soil health indicators. To achieve these aims, it combines physicochemical indicators (pH, water holding capacity, soil texture, organic matter content), with biological indicators (extracellular enzymatic activity of hydrolases, cellulose degradation capacity, and soil respiration).  Enzymatic analyses include β-glucosidase (β-GLU), urease (URE), alkaline phosphatase (PAK), acid phosphatase (PHOS) and arylsulfatase (ARS) activity, serving as proxies for major nutrient cycles (C, N, P, S). Cellulose degradation capacity represents a cost-effective, accessible, comprehensive indicator of soil functionality. Lastly, soil contamination is studied through targeted analysis of heavy metals and non-targeted screening of organic micropollutants that provides a broader understanding of the complexity of the contamination profile. Overall, grounded in systematic monitoring and supported by the HE EDAPHOS and PROLIPHYT projects, this study provides insights into the relationship between phytoremediation, contamination, and soil functionality.