4.1. Soil properties
The CaCO3 content is closely related to the increase of
pH in soil and it is associated with the generalized application of
carbonate amendments throughout the area affected by the spill
(Aguilar et al., 2004a). However, the
variations in the CaCO3 content are not very
significant, both between the different treatments applied and between
the years considered. In treatments T1 and T2, higher doses of carbonate
material were applied in relation to treatments T3 and T4, but in the
case of the former, the soils on which they were applied had a lower
initial content of carbonates and a higher degree of residual
contamination, which caused a partial dissolution of
CaCO3 that buffered the pH of the soils
(Simón et al., 2005a). In the case of
the T3 and T4 treatments, there are also no significant differences in
the carbonate content of the soils over time, since liming was carried
out at lower doses and only during the first year, since these soils
were originally carbonated and had less residual contamination, anyway,
no significant increase was observed because a partial dissolution of
calcium carbonates occurred (Simón et al.,
2008).
The reduction of the EC has been considered as a general indicator of
the degree of recovery in the area
(García-Carmona et al., 2017).
However, the soils in which T1 and T2 treatments were applied have
higher mean EC values than in the other treatments (Table 3), which is
related to the presence of residual contamination in these areas
(Martín et al., 2015).
The application of organic amendments during the restoration actions
recovered the soil OC values before the accident, so the differences
between 1998 (before the removal of the contaminated soils and the upper
part of the soils) and 2004 samplings (after completion of remediation
measures) are not significant. The evolution over time has favored the
growth of vegetation on all the GGC soils
(Pastor-Jáuregui et al., 2020), which has
promoted the contribution of organic matter to the soils and has
produced a significant increase in the OC content observed twenty years
later.