2.1. Study area
The study area includes the Guadiamar Green Corridor (GGC), affected by the toxic spill from the Aznalcóllar mine (Seville, Spain), this area is characterized by a smooth topography associated with the Guadiamar river basin (Figure 1). The affected area was around 4600 ha and was characterized by its agricultural use before the accident, where the main soil groups found were Fluvisols and Regosols, according to WRB (IUSS, 2015) or Entisols, according to SSS (2014). In all cases, these are soils with poorly developed profiles, relatively high fertility and anthropogenic influence, with grazing and fruit and cereal crops predominating (Cabrera et al., 1999, Martín Peinado, 200l). The climate of the area is conditioned by its location within the Guadalquivir Depression and the influence of the Mediterranean climate. The annual average temperature is 17.7° C (with average temperatures in the coldest months higher than 10°C) and the average annual precipitation is 612.7 mm. The annual insolation is greater than 2800 hours year-1, so the potential evapotranspiration values are higher than those of precipitation in more than 6 months a year (Martín Peinado, 200l). According to the classification of Rivas Martínez (1987), the climate is Mediterranean with drought in the summer season. Regarding the edaphic profile, the temperature regime is Thermic and the humidity regime is Xeric (USDA, 1999).