Distribution patterns of heavy metals mobility in soils of the city of Marrakech in a semiarid regio

来源 :第四届城市、工业、交通和矿山土壤国际会议(The 4th International Conference on Sol | 被引量 : 0次 | 上传用户:lianjinling27
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  Civilizations attitude towards soils has changed dramatically during the course of history.At the beginning,the alteration of this resource was limited.Progressively,with the development of human activities,the reuse of soils increased,resulting in their contamination by various organic and metallic pollutants (Adriano,1986).Land use constitute the key to soils quality in urban areas and profoundly influences soil functions due to modifications of their physical,chemical and biological properties (Wong and Gong,1998; Craul,1999; Brejda et al.,2000).Marrakech is located in one of the major agricultural areas of Morocco.This region was characterized by a huge urbanization (12 % increase from 1994 to 2004) which could have a strong impact on the urban environment and specifically on urban and peri-urban soils.The trace metals can be emitted from numerous anthropogenic activities causing the soil contamination.The soil coarse fraction,usually neglected in analyses,can nevertheless have an effect on metal concentration in the soil solution.This coarse fraction is made up of natural elements as well as technic elements constitutive of Technosols (plastic,paper,fabric,wood,bones,metallic elements and building materials).The aims of this work are (1) to have a better knowledge of the availability of metals present in the urban soils in a semiarid location (2) to achieve partial extractions of metals from three soil fractions (less than 2 ram,coarse natural and coarse technic) of selected urban soils and (3) to model and map the risk of metal dissemination in an urban environment.Samples of 68 topsoils were collected in different sites of the urban area with contrasted land uses and selected regarding to historical data.Results show that the distribution of metals content in urban soils of Marrakech vary according to land uses.Elevated metal concentrations were observed in the most anthropized soils (Technosols).Water extractable metal content shows that the less than 2-ram fraction has the main contribution to the enrichment of the soils solution by metals.The natural coarse fraction has also the highest contribution to release from these soils.It is responsible for the release of the all water extractable copper from some soils.The technic coarse fraction had a significant contribution,essentially in the most anthropized soils characterized by elevated percentage of anthropogenic elements (14 %).These results confirm that anthropogenic activity causes a wide spatial diversity of soils.It introduces different technic elements in soils that could have an impact on metal availability.It acts therefore on the metal bioavailability in the urban soils.Finally,results of urban soils of Marrakech have to be transferred to models and thematic maps for a best urban planning and development.These urban soils have to be evaluated on the basis of their value for the local ecosystem,the conservation of a healthy environment and the socio-economical requirements of a specific city.
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