The loss of soil after an ecological disaster like that in Doñana (Seville), due to the burst of a supporting wall of the reservoir containing the toxic wastes of the Aznalcollar mine (25th April 1998), can have serious repercussions for human life. Therefore, a research group of the Universidad de Granada is studying the effects of soil pollution due to heavy metals in Andalusia.
The project, supervised by Professor Carlos Dorronsoro, director of the Department of Pedology and Agricultural Chemistry, arose after the accident, when five million cubic metres of water with heavy metals and toxic mud polluted the basins of rivers Agrio and Guadiamar. After having received a commission from the Andalusian Council, the research group has developed a series of reports and treatments about the pollutant effects of these metals on soil.
The aim of the study is to analyse how soils evolve if we do not carry out the necessary cleaning work after a toxic spillage. All the areas polluted by the toxic mud has been cleaned, with the exception of some redoubts preserved to find out the effects of the presence of these toxic substances on soil.
Toxic waste
The work method reveals how the mud releases a series of wastes in some experimental plots in the area of the Vado del Quema due to the fact that, when it rains, the mud (which had oxidized on the soil surface) releases an extremely acid solution with a high concentration of dissolved metals which seep from the surface altering and polluting it, and destroying all the soil.
The most immediate consequence observed after the studio is the formation of an alteration layer in the soils of these experimentation plots which has increased its thickness little by littler: two months after having started the research work the waste was four millimetre thick; one year later, fifteen, and now, seven years after, it is one hundred and ten millimetre thick.
This way, all the properties and minerals of this soil have changed; it is completely infertile now and unable to support life.
The research work will allow to apply the results to develop cleaning works in case of pollution and deduce the need, urgency and depth of these works, this is, how much soil must be cleaned to cancel the effects of the mud layer.
Soil erosion
Another work line of the group supervised by professor Dorronsoro revolves around the fight against soil erosion, a problem much more generalized and serious than pollution. The researchers of the UGR have warned that the solution to the problem of the use of soil comes form the so-called ‘conservation agriculture’, this is, using the natural conditions of the environment.
Thanks to this technique, a soil which took 100,000 years to form recovers its superficial horizon, the most fertile, in 10 or 15 years. The object of the system is to leave the crop waste on the soil surface; as they are nutrients (such as carbon and nitrogen), they create a layer with se organic matter able to give soil the necessary fertility.
It could be done using the remains of the crop as the dead leaves that remain on the surface in a forest. Little by little, it gets transformed and, eventually, the remains of organic matter (humus) penetrate on the ground.
The secret of this agriculture is to keep the ground covered by remains; this way, when it rains, on the one hand, it impacts on them without breaking the soil minerals and without eroding it and, on the other hand, when remains structure soil increasing its infiltration capacity and reducing the run-off that would erode the ground sweeping away the soil particles.
Reference:
Prof Carlos Dorronsoro Fernández. Department of Pedology and Agricultural Chemistry of the Universidad de Granada.
Phone numbers. 958 248 433 – 248 537. E-mail: cfdorron@ugr.es
