The Wadi-Fira region in eastern Chad is facing dramatic water supply problems, related to the climatic semi-arid context and the reception of refugees from the Darfour, which has increased the local population by 22% ...The Wadi-Fira region in eastern Chad is facing dramatic water supply problems, related to the climatic semi-arid context and the reception of refugees from the Darfour, which has increased the local population by 22% these last years. Expansion of agglomerations (temporary new towns), development of agricultural and pastoral practices together with the augmentation of the population have led to dramatic water needs. The basement aquifer of Wadi-Fira constitutes the main source of water supply. However, little is known about this system. Within this context, this work aims at better understanding and identifying hydrogeochemical processes and their relations to groundwater quality within this complex environment, and groundwater recharge mechanisms. 31 groundwater samples were collected at two sites, Am Zoer and Guereda-Iriba, from hand dug wells and deep wells. Major chemical elements were analyzed on all samples and stables isotopes (oxygen-18 and deuterium) on 17 samples. Various methods were used to interpret the hydrochemical data (descriptive and multivariate statistics, Piper and Schoeller diagrams, scatter plots, minerals saturation indices). The stable isotopes were interpreted using conventional IAEA methods. The results permitted to differentiate the laterite reservoir from the deep fractured reservoir. The main process controlling groundwater mineralization is water-rocks interaction and natural minerals dissolution. Ion exchanges, evaporation and anthropogenic activities have also a moderate impact on groundwater quality. Based on isotopes data, it is concluded that groundwater in the basement aquifer is related with modern rainfall. These results provide further insights into this basement aquifer, which is a vital resource for the region of Wadi-Fira.展开更多
In the east of Chad,precisely in Tchaga,gold is mined in an artisanal manner.This gold panning activity contributes to the income of rural populations.However,this activity uses chemical processes involving mercury an...In the east of Chad,precisely in Tchaga,gold is mined in an artisanal manner.This gold panning activity contributes to the income of rural populations.However,this activity uses chemical processes involving mercury and cyanide which cause impacts on surface water and groundwater.In a context of favor-able gold prices,the number of artisanal mines is increasing and it is interesting to dwell on the question,also understanding that few studies have been carried out,until now,on gold panning in relationship with environmental aspects.The present study then consists of evaluating the impacts of gold panning on the environment on the Tchaga sites.To understand the phenomenon and quantify it,it was necessary to carry out a combinatorial analysis of the surface and underground waters of the study area.The results obtained indicate that the negative impacts of gold panning on soils range from moderate to high with a reduction in arable land.The methodology used consists of water sampling,measuring physical parameters and using methods to determine the concen-trations of cations and anions.After analyzing the results of ETM analysis in the water,it appears that the water is not very loaded with ETM and heavy metals.The water contains average concentrations(0.001 mg/l in As,0.003 mg/l in Pb and 0.001 mg/l in Zn or even zero for mercury)which are generally lower than WHO standards.In surface waters,the concentration of Hg is 0.000 mg/l and that of Zn is 0.002 mg/l.Values below the limit values set by the WHO do not indicate any presence of apparent contamination by gold panning ac-tivities at least for the moment.In groundwater,the mercury concentration is zero compared to the limit value set by the WHO,this is due either to the quan-tity of the product,the sampling,or the time of contamination.On the other hand,zinc has a low value compared to the limit value set by the drinking water standards in Chad.While the arsenic concentration(0.002 mg/l)does not reach the limit value set by the WHO(0.01 mg/l).展开更多
文摘The Wadi-Fira region in eastern Chad is facing dramatic water supply problems, related to the climatic semi-arid context and the reception of refugees from the Darfour, which has increased the local population by 22% these last years. Expansion of agglomerations (temporary new towns), development of agricultural and pastoral practices together with the augmentation of the population have led to dramatic water needs. The basement aquifer of Wadi-Fira constitutes the main source of water supply. However, little is known about this system. Within this context, this work aims at better understanding and identifying hydrogeochemical processes and their relations to groundwater quality within this complex environment, and groundwater recharge mechanisms. 31 groundwater samples were collected at two sites, Am Zoer and Guereda-Iriba, from hand dug wells and deep wells. Major chemical elements were analyzed on all samples and stables isotopes (oxygen-18 and deuterium) on 17 samples. Various methods were used to interpret the hydrochemical data (descriptive and multivariate statistics, Piper and Schoeller diagrams, scatter plots, minerals saturation indices). The stable isotopes were interpreted using conventional IAEA methods. The results permitted to differentiate the laterite reservoir from the deep fractured reservoir. The main process controlling groundwater mineralization is water-rocks interaction and natural minerals dissolution. Ion exchanges, evaporation and anthropogenic activities have also a moderate impact on groundwater quality. Based on isotopes data, it is concluded that groundwater in the basement aquifer is related with modern rainfall. These results provide further insights into this basement aquifer, which is a vital resource for the region of Wadi-Fira.
文摘In the east of Chad,precisely in Tchaga,gold is mined in an artisanal manner.This gold panning activity contributes to the income of rural populations.However,this activity uses chemical processes involving mercury and cyanide which cause impacts on surface water and groundwater.In a context of favor-able gold prices,the number of artisanal mines is increasing and it is interesting to dwell on the question,also understanding that few studies have been carried out,until now,on gold panning in relationship with environmental aspects.The present study then consists of evaluating the impacts of gold panning on the environment on the Tchaga sites.To understand the phenomenon and quantify it,it was necessary to carry out a combinatorial analysis of the surface and underground waters of the study area.The results obtained indicate that the negative impacts of gold panning on soils range from moderate to high with a reduction in arable land.The methodology used consists of water sampling,measuring physical parameters and using methods to determine the concen-trations of cations and anions.After analyzing the results of ETM analysis in the water,it appears that the water is not very loaded with ETM and heavy metals.The water contains average concentrations(0.001 mg/l in As,0.003 mg/l in Pb and 0.001 mg/l in Zn or even zero for mercury)which are generally lower than WHO standards.In surface waters,the concentration of Hg is 0.000 mg/l and that of Zn is 0.002 mg/l.Values below the limit values set by the WHO do not indicate any presence of apparent contamination by gold panning ac-tivities at least for the moment.In groundwater,the mercury concentration is zero compared to the limit value set by the WHO,this is due either to the quan-tity of the product,the sampling,or the time of contamination.On the other hand,zinc has a low value compared to the limit value set by the drinking water standards in Chad.While the arsenic concentration(0.002 mg/l)does not reach the limit value set by the WHO(0.01 mg/l).
