Spontaneous ecological recovery of vegetation in a red gypsum landfill: Betula pendula dominates after 10 years of inactivity

Red gypsum is the product of the neutralization of titanium dioxide (TiO2) extraction residue from ilmenite and anatase. The disposal of red gypsum creates heterogeneous plots with layers that may include Fe, Ca, Al, Mg, Mn, S, and other elements and an alkaline pH that makes revegetation complicated and slow. The vertical and horizontal dispersion of the sediment particles are the main concern. Therefore, the establishment of precise vegetation cover is needed to address this issue. One of the aims of this study was (1) to explore the distribution of the spontaneous vegetation found along a red gypsum-formed landfill located at the Ochsenfeld site in eastern France. Additionally, (2) some pedological parameters were also studied to determine the most significant red gypsum chemical drivers influencing the occurrence and abundance of the vegetation within the site. The Braun-Blanquet scale was used to rate the species presence in the field contained in the spontaneous vegetation dataset. The vegetation survey revealed the presence of 59 species from 23 families. The most abundant species was Betula pendula, and a further cluster analysis enabled the differentiation of areas with this species. The CaCl2 extractable concentrations of the nutrients and trace elements, as well as the pH and the organic matter (OM) present in the sampled substrate, were used to form the pedological parameters dataset. A multiple factor analysis (MFA) was performed to link the large datasets together and revealed 3 groups of plants. Group 1 was composed of pH-tolerant species such as B. pendula and S. caprea. Group 2 was formed by Cr-Zn-tolerant species, including Echium vulgare and R. pseudoacacia. Finally, group 3 was characterized by species such as Clematis vitalba and Artemisia vulgaris that tolerate the presence of Na. The MFA revealed a correlation between the Betula pendula distribution and the pH, CaCl2 extractable P concentration and organic matter. On the other hand, A lack of relation of the CaCl2 extractable concentrations of Fe, Mn, Na, Si and K were also found. This study aided in the selection of an adapted candidate for the implementation of the revegetation strategy of a red gypsum landfill in eastern France. Further tests were performed at the site using white birch for Mn accumulation and topsoil stabilization in situ.