Evaluation of amendment addition and tree planting as measures to remediate contaminated soils: The Guadiamar case study (SW Spain)

Publication date: July 2018
Source:CATENA, Volume 166
Author(s): P. Madejón, M.T. Domínguez, M. Gil-Martínez, C.M. Navarro-Fernández, M.M. Montiel-Rozas, E. Madejón, J.M. Murillo, F. Cabrera, T. Marañón
Soil pollution is one of the main environmental concerns at a global scale, and different measures have been proposed for its prevention and remediation. In this paper we evaluate two measures – amendment addition and tree planting – applied to remediate soils contaminated by trace elements (TE). The Guadiamar study site (SW Spain) is a well-known example of a large-scale cleaning and remediation program intended to rehabilitate about 3000 ha of soils affected by a mine-spill in 1998. Firstly, we present the results of a long-term experiment in which two types of amendments – sugar beet lime (SL) and biosolid compost (BC) – were added to the spill-affected soil. Three different treatments were established: SL, BC, and NA (non-amended control). The experiment has been running since 2002 and new soil samples were taken in 2016. In general, the amendments increased soil pH and total organic carbon, and reduced TE availability. The available TE concentrations (CaCl2 extraction) decreased drastically with time in all cases, but the evolution differed among treatments. The treatment effectiveness was evaluated by measuring plant biomass, TE concentrations in plant shoots, and soil-plant transfer. Secondly, we present results detailing the effects of seven tree species (three - Populus alba, Celtis australis, and Fraxinus angustifolia - were deciduous and four - Quercus ilex, Olea europaea, Ceratonia siliqua, and Pinus pinea - evergreen) on remediated soils. In 2014 (about 15 years after planting) we measured TE concentrations in leaves and roots and related them with TE concentrations (total and available) in soil. There were significant differences among the studied tree species in the uptake and accumulation of TE in leaves and roots. Soil pH differed among tree species and with respect to adjacent non-planted sites. There was a negative exponential relationship between soil pH and availability of Cd, Cu, and Zn. The bioconcentration factor (BCF, root:soil) and the translocation factor (TF, leaf:root) were calculated to evaluate the potential of each tree species to stabilize TE in soil. Finally, we propose the phytoremediation of TE-contaminated soils as a three-stage process, including addition of soil amendments, planting of trees, and monitoring of TE dynamics.

Graphical abstract

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