Fethi LACHAAL is a CETRE researcher-assistant professor. He holds a PhD and a Master degree, in Hydrogeology and Geophysics, from Carthage University in the framework of cooperation between INAT, CERTE, and IRD. He is a permanent member in the Georesources Laboratory (INRST and CETRE, Minister of Higher Education and Scientific Research in Tunisia) form 2002, and LMI NAÏLA: : Managing water resources in tunisian rural areas from 2017. He has leaded several projects sponsored by the Minister of Higher Education and Scientific Research in Tunisia and the Minister of Agriculture of Tunisia. He is the coordinator of research project "the Tunisian "dorsal" and its confines: water potential, reservoirs and quality for integrated water resources management (CERTE/MEREST, 2015-2019)".He interests lie in aquifer investigation, hydro-geophysics, hydrodynamic, MODFLOW groundwater modeling, and groundwater recharge. He has more than 16 years of experience in field experiments and research developments designed for arid and semi-arid groundwater characterization and sustainable management. Address: Borj Cedria Technopark, Tunisia.Address: BP: 273 Soliman 8020 Tunisie
In this study, geochemical tracers and geophysical methods were combined to assess the anthropoge... more In this study, geochemical tracers and geophysical methods were combined to assess the anthropogenic aquifer recharge (AAR) processes within a small floodplain in Mornag plain, NE of Tunisia. From a regional viewpoint, the aquifer is one of the most exploited because of the intensive agricultural and industrial activities in the region. Based on geochemical data and hydrodynamic observations, stream–aquifer connection was evidently proven. An AAR from the saline effluent rejected in the dry channel (the Wadi) was detected in the downstream area of the Wadi El Hma plain. Isotopic tracers ( 18 O and 2 H) were effective tools to clarify the recharge processes in relation to the hill dam to detect the signature of the effluent near an installed check dam. Electrical resistivity tomography (ERT) profiles were performed in the most salinized part of the plain in order to highlight the role of the Wadi in AAR. ERT provided clear images of low resistivity horizons longitudinally and transversely to the Wadi. Because groundwater is mainly used for irrigation in the Wadi El Hma plain, an assessment of its suitability for irrigation was performed based on a multi-criteria decision analysis, which revealed that, except the hill dam water and upstream groundwater, the remaining zones of the aquifer are providing water classified as doubtful to unsuitable for irrigation. The results of this work highlight the water sustainability threat in the region and would warn decision-makers to control the Wadi runoff and preserve it against any pollution source since it constitutes the principal inlet of any AAR.
<p>Semi-arid areas are usually associated with decreasing water levels due to groun... more <p>Semi-arid areas are usually associated with decreasing water levels due to groundwater overexploitation, that threatens the sustainability of the water resource and causes negative environmental impacts. More surprisingly, semi-arid areas also host situations of long-term rising groundwater levels, due to anthropization. Changes in land use and land cover, surface application of groundwater pumped from deeper aquifers, inflow of external resources or insufficient sanitation may generate a significant rise in groundwater levels. Consequences on the local water balance may be not less dramatic than those of overexploitation, as rising groundwater tables compromise i) medium term agriculture, via waterlogging and salinization of soils, ii) urban development, via the saturation of drainage systems and water networks and iii) the environment, via the increase in groundwater discharges towards low-topography areas or surface water masses. Qualitative consequences include the death of crops by hypoxia, the increase of water diseases, or the eutrophication of surface water masses. Illustrated by lessons learnt from Mauritania, Niger, Algeria, Australia and Spain, this paper proposes a typology of contexts and associated consequences. It also illustrates implemented or proposed remediation actions, acting from the causes (land-use restrictions, implementation of drip irrigation, enhancement of sewage networks) to the effects (green belt around cities, drainage of agricultural plots for downstream or more remote rejection, groundwater abstraction at regional scale for further treatment). In a wider scale, this paper highlights a less visible but crucial aspect of the need to anticipate anthropogenic and climatic impacts on groundwater evolution at several timescales</p>
In addition to their agricultural role, Tunisian hill dams provide important water volumes for Ma... more In addition to their agricultural role, Tunisian hill dams provide important water volumes for Managed Aquifer Recharge (MAR) through water release in wadis such as the cases of Wadi Khairat in Sousse prefecture, Sahel of Tunisia. The aim of this study is to evaluate the Tunisian experience in MAR throughout assessing the efficiency of water release from hill dams for the artificial recharge of the shallow stressed aquifers. Frequent field observations were conducted between 2013 and 2015, and during them, physical and geochemical parameters of stream, dam and well waters were measured. MAR efficiency is firstly assessed based on WTF method. Furthermore, based on the geochemical and isotopic data, an End Member Mixing Analysis (EMMA) model was used to calculate the contribution of released dam water in aquifer recharge. Results show that dam water release is playing an important role in aquifer recharge and its contribution exceeds 70% in some locations. Recharge amount is clearly depending on the released volume, climatic conditions and wadi lithology and morphology. The present MAR method is more efficient in Wadi underlying aquifer. This concept is strongly encouraged to be applied in stressed aquifers where an excess of surface water might exist during rainy periods in order to guarantee the sustainability of these resources.
The main objectives of this paper are to get a better understand of the rainfall space-time varia... more The main objectives of this paper are to get a better understand of the rainfall space-time variability and to assess its rainfall tendency in the Merguellil basin, central Tunisia, by means of statistical tests. We assessed the rainfall at seasonal and monthly scales. Based on the availability of a continuous good record, eleven rain gauges were carefully chosen. Monthly rainfall data range from 1980 to 2016. Two tests are used to examine the trends: the non-parametric Mann–Kendall and Sen’s slope were selected to detect the existence, with a statistical significance, of an increase or a decrease in rainfall data trend. Results revealed high space-time variability of rainfall showing significant changes in seasonal and monthly rainfall amounts, for the studied period, particularly for summer months. The rise ranges from 0.68 mm/yr to 2.08 mm/yr and the highest values are observed in the basin upstream. Consequently, there are signs of a considerable rainfall raise in the basin. Increasing trends in summer, especially in July and August, were detected in the majority of studied rain gauges, where the monthly upward varies between 0.46 mm/yr and 0.83 mm/year. Most of the calculated slopes are statistically significant and the changes in Merguellil basin are more significant compared to other studies.
The Grombalia plain (Northeastern Tunisia) is one of the most important hydrogeologic systems in ... more The Grombalia plain (Northeastern Tunisia) is one of the most important hydrogeologic systems in Tunisia. Despite the various geological, structural, and hydrogeological studies and due to the tectonic and sedimentary complexity affecting the region, the geometric characterization of the Grombalia Plain aquifer system remains incompletely known. So it is very important to conduct multidisciplinary research in order to understand the geometrical configuration of this system. This characterization is based especially on the analysis and the interpretation of deep oil wells, the seismic reflection sections, and the gravity data. Hydrogeophysical investigations show that the Grombalia aquifers are constituted by two major aquifers: (1) the Mio-Plio-Quaternary to Quaternary multilayer shallow to deep aquifer and (2) the Miocene-Oligocene deep aquifer. The structural isochron map inferred from seismic data as well as the gravity mapping based on different techniques of analysis and interpretation (total horizontal derivative, source edge detect filter, tilt angle filter, Euler Deconvolution solutions) shows more details about the deep structure and the limits of this hydrogeological system. Finally, the produced structural map of Top Langhian in Grombalia plain can be considered a very useful document for future deep-water targets exploration and their sustainable management. Also, this paper will be the key and the base for future hydrogeological modeling of the region.
Water environment research : a research publication of the Water Environment Federation, Jan 8, 2016
A multivariate statistical analysis used with geophysical investigation enabled the assessment of... more A multivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge is varying from 1.4 % in the upstream region of Wadi Al Ayn to 77 % near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn is varying from 1 % to 13 %; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region...
El Haouaria aquifer (northeast Tunisia) is one of the typical examples of semi-arid coastal aquif... more El Haouaria aquifer (northeast Tunisia) is one of the typical examples of semi-arid coastal aquifers which have been intensively exploited during the last few years. In order to implement a strategy of sustainable groundwater management of El Haouaria aquifer a proper understanding of the hydrogeological systems is necessary. In this context, a multi-tracer approach has been carried out in the El Haouaria aquifer system, based on major ions and stable isotopes analysis. The piezometric study confirms the overexploitation of the aquifer, especially at the centre of the aquifer, where the water table is lowered 2.5 m below sea level. The geochemical data was used to characterize and classify water samples and studying the water–rock interaction based on a multitude of ion plots and diagrams. Stable isotopes were useful tools to provide valuable information about the origin and the circulation patterns, to understand the recharge processes, and to differentiate between mineralization o...
Due to the growing water demand, especially for the agricultural development, the water managemen... more Due to the growing water demand, especially for the agricultural development, the water management in the Grombalia region (NE Tunisia) exploits multiple sources of water. Rainfall is marked by a strong seasonal and interannual variability in time and over space. The regional aquifer has been intensively used for irrigation. Artificial groundwater recharge has been initiated in 1975, in order to reduce the piezometric depletion. It is fed by an important surface water transfer from the North-West of Tunisian since 1984 and by 3 local dams. As a consequence, the Grombalia aquifer system has undergone multiple hydrodynamic and hydrochemical changes, affecting it deeply during the last decades. This study investigates their consequences on the groundwater quantity and quality. In this context, a multi-tracer approach was carried out in the Grombalia basin, based on 4 field visits between March 2013 and April 2015. The recent piezometric decline varying between 0 and −18 m in the upstre...
The 130 Mm3-capacity Mellègue reservoir has a broad catchment area. Contaminants include sewage f... more The 130 Mm3-capacity Mellègue reservoir has a broad catchment area. Contaminants include sewage from cities, farm fertilizers, and metals released from mine tailings, all of which threaten Tunisia’s water supply. Forty surface water samples were collected from watercourses and 18 from the reservoir during the wet and dry seasons. To evaluate groundwater contamination, the Sarrat basin was considered as a case study, and well water was analysed. The total amounts of base metals and nutrients in the watercourses did not exceed international standards. Evaporites in broad Triassic outcrops and in tailings dissolve, and may fix lead as sulphates; however, sulphate and chloride can complex and increase the solubility of some metals. The nutrient and salt content were highest in the Rmel River, which receives sewage from el Kef. An opposing gradient of metals was observed in the reservoir water column: elements such as Zn, Pb, and Al were enriched upwards, while Mn, Fe, and Cr increased towards the sediment–water interface. The same behaviour was observed for NO3− and O2, due to metal release under reducing conditions in bottom waters, and dissolution of Fe and Mn colloids. Fertilizers and sewage may be responsible for the potentially hazardous level of nutrients in the groundwater.ZusammenfassungDer 130 Millionen m³ große Mellègue-Speicher hat ein weites Einzugsgebiet. Schadstoffe aus urbanen Abwässern, Düngemitteln und Metallen aus Tailings sind ein Bedrohung für die Wasserversorgung in Tunesien. Während der Trocken- und Regenzeit wurden vierzig Oberflächenwasserproben aus Gewässern und achtzehn aus dem Speicher entnommen. Am Fallbeispiel des Sarrat-Beckens wurden zudem Brunnenwasserproben analysiert, um Grundwasserbelastungen zu untersuchen. Die Gesamtgehalte an unedlen Metallen und Nährstoffen im Oberflächengewässer liegen nicht über internationalen Standards. Durch lösliche Evaporite, welche in den weiten Ausstrichbereichen triassischer Gesteine und in Tailings vorkommen, kann Blei sulfatisch gebunden werden. Andererseits besteht die Möglichkeit, dass Sulfat- und Chloridkomplexe die Löslichkeit einiger Metalle beeinflussen. Die Nährstoff- und Salzgehalte waren im Rmel-River, welchem Abwässer aus El Kef zufließen, am höchsten. Ein umgekehrter Metall-Konzentrationsgradient wurde in der Wassersäule des Wasserspeichers festgestellt. Zink, Blei und Aluminium waren im oberen Abschnitt angereichert, wohingegen Mangan, Eisen und Chrom in Richtung der Sediment-Wasser Grenze zunahmen. Das gleiche Verhalten wurde für Nitrat und Sauerstoff aufgrund von Metallfreisetzungen unter reduzierenden Bedingungen sowie der Lösung von Eisen- und Mangankolloiden im bodennahen Wasser beobachtet. Düngemittel und Abwässer sind vermutlich verantwortlich für die sehr hohen Nähstoffgehalte im Grundwasser.ResumenEl reservorio de 130 Mm3 de capacidad de Mellègue tiene una amplia cuenca. Los contaminantes incluyen las aguas residuales provenientes de distintas ciudades, fertilizantes de granjas y metales liberados desde colas de mina, y amenazan el suministro de agua de Túnez. Cuarenta muestras de agua superficial fueron colectadas desde cursos de agua y 18 desde el reservorio durante las estaciones secas y húmedas. Para evaluar la contaminación del agua subterránea, se consideró la cuenca Sarrat como un caso de estudio y se analizó el agua potable. Las cantidades totales de metales base y nutrientes en los cursos de agua no excedió los estándares internacionales. Las evaporitas en los grandes afloramientos triásicos y en las colas se disuelven y pueden fijar plomo como sulfatos; sin embargo, sulfato y cloruro pueden complejar e incrementar la solubilidad de algunos metales. Los contenidos en nutrientes y sales fueron máximos en el río Rmel que recibe aguas residuales desde el Kef. Un gradiente opuesto de metales fue observado en el agua del reservorio: elementos como Zn, Pb y Al se enriquecieron hacia la superficie mientras Mn, Fe y Cr se incrementaron hacia la interface sedimento-agua. El mismo comportamiento fue observado para NO3- y O2, debido a la liberación de metales bajo condiciones reductores en las aguas del fondo y la disolución de coloides de Fe y Mn. Los fertilizantes y las aguas residuales podrían ser los responsables por el nivel potencialmente peligroso de nutrientes en el agua subterránea.突尼斯西北部Mellegue流域水样及环境碱金属特征Mellegue水库汇水面积大,库容量达130×106m3。水体污染物主要源自城市废水、农用化肥、尾矿释放等,它们对突尼斯供水构成巨大威胁。分别在干、枯季从汇水河道取地表水样40个和水库水样18个;同时,为评价区域地下水污染状况,分析了Sarrat盆地泉水水样特征。河道水样的碱金属和养分含量未超国际水质标准。研究区内大面积三叠纪蒸发盐岩露头和尾矿露头发生溶解作用,铅被固定为硫酸盐,硫酸盐和氯化物混合作用进一步促进某些金属离子溶解。Rmel河因接受el Kef城市废水而养分和盐含量最高。水库水样呈现相反梯度变化:锌、铅和铝向上富集,而锰、铁和镉向底部水-岩界面富集。底水还原环境金属离子释放和铁锰胶体溶解作用使NO3-和O2含量具有相同变化规律。农用化肥和城市废水污染是地下水呈养分超标趋势的主要原因.
Like all other Mediterranean countries, Tunisia provides multiple examples of groundwater degrada... more Like all other Mediterranean countries, Tunisia provides multiple examples of groundwater degradation due to its overexploitation. This is especially the case in the Zeramdine-Mahdia-Jebeniana region (central east Tunisia), where recent measurements revealed an important piezometric drop in the Miocene aquifers. Through hydrodynamic and hydrochemical analysis, we studied the influence of the head decrease on groundwater flow and quality. The spatial and temporal analysis of the piezometry identified two totally independent compartments. This was confirmed by the hydrogeochemical and multivariate statistical analysis. The Miocene aquifer system was divided into two water groups: (1) the Zeramdine-Beni Hassen aquifer which is characterized by freshwater, Na-Ca-Cl-SO 4 facies, and salinity increase from west to east that is coinciding with the principal water flow direction; and (2) the Mahdia-Ksour Essef aquifer, which is defined throughout by high and heterogeneous salinity and Na-Cl...
In this study, geochemical tracers and geophysical methods were combined to assess the anthropoge... more In this study, geochemical tracers and geophysical methods were combined to assess the anthropogenic aquifer recharge (AAR) processes within a small floodplain in Mornag plain, NE of Tunisia. From a regional viewpoint, the aquifer is one of the most exploited because of the intensive agricultural and industrial activities in the region. Based on geochemical data and hydrodynamic observations, stream–aquifer connection was evidently proven. An AAR from the saline effluent rejected in the dry channel (the Wadi) was detected in the downstream area of the Wadi El Hma plain. Isotopic tracers ( 18 O and 2 H) were effective tools to clarify the recharge processes in relation to the hill dam to detect the signature of the effluent near an installed check dam. Electrical resistivity tomography (ERT) profiles were performed in the most salinized part of the plain in order to highlight the role of the Wadi in AAR. ERT provided clear images of low resistivity horizons longitudinally and transversely to the Wadi. Because groundwater is mainly used for irrigation in the Wadi El Hma plain, an assessment of its suitability for irrigation was performed based on a multi-criteria decision analysis, which revealed that, except the hill dam water and upstream groundwater, the remaining zones of the aquifer are providing water classified as doubtful to unsuitable for irrigation. The results of this work highlight the water sustainability threat in the region and would warn decision-makers to control the Wadi runoff and preserve it against any pollution source since it constitutes the principal inlet of any AAR.
<p>Semi-arid areas are usually associated with decreasing water levels due to groun... more <p>Semi-arid areas are usually associated with decreasing water levels due to groundwater overexploitation, that threatens the sustainability of the water resource and causes negative environmental impacts. More surprisingly, semi-arid areas also host situations of long-term rising groundwater levels, due to anthropization. Changes in land use and land cover, surface application of groundwater pumped from deeper aquifers, inflow of external resources or insufficient sanitation may generate a significant rise in groundwater levels. Consequences on the local water balance may be not less dramatic than those of overexploitation, as rising groundwater tables compromise i) medium term agriculture, via waterlogging and salinization of soils, ii) urban development, via the saturation of drainage systems and water networks and iii) the environment, via the increase in groundwater discharges towards low-topography areas or surface water masses. Qualitative consequences include the death of crops by hypoxia, the increase of water diseases, or the eutrophication of surface water masses. Illustrated by lessons learnt from Mauritania, Niger, Algeria, Australia and Spain, this paper proposes a typology of contexts and associated consequences. It also illustrates implemented or proposed remediation actions, acting from the causes (land-use restrictions, implementation of drip irrigation, enhancement of sewage networks) to the effects (green belt around cities, drainage of agricultural plots for downstream or more remote rejection, groundwater abstraction at regional scale for further treatment). In a wider scale, this paper highlights a less visible but crucial aspect of the need to anticipate anthropogenic and climatic impacts on groundwater evolution at several timescales</p>
In addition to their agricultural role, Tunisian hill dams provide important water volumes for Ma... more In addition to their agricultural role, Tunisian hill dams provide important water volumes for Managed Aquifer Recharge (MAR) through water release in wadis such as the cases of Wadi Khairat in Sousse prefecture, Sahel of Tunisia. The aim of this study is to evaluate the Tunisian experience in MAR throughout assessing the efficiency of water release from hill dams for the artificial recharge of the shallow stressed aquifers. Frequent field observations were conducted between 2013 and 2015, and during them, physical and geochemical parameters of stream, dam and well waters were measured. MAR efficiency is firstly assessed based on WTF method. Furthermore, based on the geochemical and isotopic data, an End Member Mixing Analysis (EMMA) model was used to calculate the contribution of released dam water in aquifer recharge. Results show that dam water release is playing an important role in aquifer recharge and its contribution exceeds 70% in some locations. Recharge amount is clearly depending on the released volume, climatic conditions and wadi lithology and morphology. The present MAR method is more efficient in Wadi underlying aquifer. This concept is strongly encouraged to be applied in stressed aquifers where an excess of surface water might exist during rainy periods in order to guarantee the sustainability of these resources.
The main objectives of this paper are to get a better understand of the rainfall space-time varia... more The main objectives of this paper are to get a better understand of the rainfall space-time variability and to assess its rainfall tendency in the Merguellil basin, central Tunisia, by means of statistical tests. We assessed the rainfall at seasonal and monthly scales. Based on the availability of a continuous good record, eleven rain gauges were carefully chosen. Monthly rainfall data range from 1980 to 2016. Two tests are used to examine the trends: the non-parametric Mann–Kendall and Sen’s slope were selected to detect the existence, with a statistical significance, of an increase or a decrease in rainfall data trend. Results revealed high space-time variability of rainfall showing significant changes in seasonal and monthly rainfall amounts, for the studied period, particularly for summer months. The rise ranges from 0.68 mm/yr to 2.08 mm/yr and the highest values are observed in the basin upstream. Consequently, there are signs of a considerable rainfall raise in the basin. Increasing trends in summer, especially in July and August, were detected in the majority of studied rain gauges, where the monthly upward varies between 0.46 mm/yr and 0.83 mm/year. Most of the calculated slopes are statistically significant and the changes in Merguellil basin are more significant compared to other studies.
The Grombalia plain (Northeastern Tunisia) is one of the most important hydrogeologic systems in ... more The Grombalia plain (Northeastern Tunisia) is one of the most important hydrogeologic systems in Tunisia. Despite the various geological, structural, and hydrogeological studies and due to the tectonic and sedimentary complexity affecting the region, the geometric characterization of the Grombalia Plain aquifer system remains incompletely known. So it is very important to conduct multidisciplinary research in order to understand the geometrical configuration of this system. This characterization is based especially on the analysis and the interpretation of deep oil wells, the seismic reflection sections, and the gravity data. Hydrogeophysical investigations show that the Grombalia aquifers are constituted by two major aquifers: (1) the Mio-Plio-Quaternary to Quaternary multilayer shallow to deep aquifer and (2) the Miocene-Oligocene deep aquifer. The structural isochron map inferred from seismic data as well as the gravity mapping based on different techniques of analysis and interpretation (total horizontal derivative, source edge detect filter, tilt angle filter, Euler Deconvolution solutions) shows more details about the deep structure and the limits of this hydrogeological system. Finally, the produced structural map of Top Langhian in Grombalia plain can be considered a very useful document for future deep-water targets exploration and their sustainable management. Also, this paper will be the key and the base for future hydrogeological modeling of the region.
Water environment research : a research publication of the Water Environment Federation, Jan 8, 2016
A multivariate statistical analysis used with geophysical investigation enabled the assessment of... more A multivariate statistical analysis used with geophysical investigation enabled the assessment of interaction between saline surface water and groundwater in the coastal plain of Wadi Al Ayn and Daroufa in CapBon peninsula, north-east Tunisia. The application of the Principal Component Analysis (PCA) identified the end members which contribute to groundwater recharge: the wastewater infiltrated from Wadi Al Ayn, the oilfield brine infiltrated to the aquifer through the sandy bed of Wadi Al Ayn, the intruded seawater near Wadi Daroufa in the downstream region and the fresh groundwater flowing from the upstream region. The contribution of wastewater in groundwater recharge is varying from 1.4 % in the upstream region of Wadi Al Ayn to 77 % near its downstream part. The fraction of oilfield brine mixed with groundwater in the alluvial aquifer under Wadi Al Ayn is varying from 1 % to 13 %; whereas the fraction of intruded seawater into the coastal part of the aquifer near Daroufa region...
El Haouaria aquifer (northeast Tunisia) is one of the typical examples of semi-arid coastal aquif... more El Haouaria aquifer (northeast Tunisia) is one of the typical examples of semi-arid coastal aquifers which have been intensively exploited during the last few years. In order to implement a strategy of sustainable groundwater management of El Haouaria aquifer a proper understanding of the hydrogeological systems is necessary. In this context, a multi-tracer approach has been carried out in the El Haouaria aquifer system, based on major ions and stable isotopes analysis. The piezometric study confirms the overexploitation of the aquifer, especially at the centre of the aquifer, where the water table is lowered 2.5 m below sea level. The geochemical data was used to characterize and classify water samples and studying the water–rock interaction based on a multitude of ion plots and diagrams. Stable isotopes were useful tools to provide valuable information about the origin and the circulation patterns, to understand the recharge processes, and to differentiate between mineralization o...
Due to the growing water demand, especially for the agricultural development, the water managemen... more Due to the growing water demand, especially for the agricultural development, the water management in the Grombalia region (NE Tunisia) exploits multiple sources of water. Rainfall is marked by a strong seasonal and interannual variability in time and over space. The regional aquifer has been intensively used for irrigation. Artificial groundwater recharge has been initiated in 1975, in order to reduce the piezometric depletion. It is fed by an important surface water transfer from the North-West of Tunisian since 1984 and by 3 local dams. As a consequence, the Grombalia aquifer system has undergone multiple hydrodynamic and hydrochemical changes, affecting it deeply during the last decades. This study investigates their consequences on the groundwater quantity and quality. In this context, a multi-tracer approach was carried out in the Grombalia basin, based on 4 field visits between March 2013 and April 2015. The recent piezometric decline varying between 0 and −18 m in the upstre...
The 130 Mm3-capacity Mellègue reservoir has a broad catchment area. Contaminants include sewage f... more The 130 Mm3-capacity Mellègue reservoir has a broad catchment area. Contaminants include sewage from cities, farm fertilizers, and metals released from mine tailings, all of which threaten Tunisia’s water supply. Forty surface water samples were collected from watercourses and 18 from the reservoir during the wet and dry seasons. To evaluate groundwater contamination, the Sarrat basin was considered as a case study, and well water was analysed. The total amounts of base metals and nutrients in the watercourses did not exceed international standards. Evaporites in broad Triassic outcrops and in tailings dissolve, and may fix lead as sulphates; however, sulphate and chloride can complex and increase the solubility of some metals. The nutrient and salt content were highest in the Rmel River, which receives sewage from el Kef. An opposing gradient of metals was observed in the reservoir water column: elements such as Zn, Pb, and Al were enriched upwards, while Mn, Fe, and Cr increased towards the sediment–water interface. The same behaviour was observed for NO3− and O2, due to metal release under reducing conditions in bottom waters, and dissolution of Fe and Mn colloids. Fertilizers and sewage may be responsible for the potentially hazardous level of nutrients in the groundwater.ZusammenfassungDer 130 Millionen m³ große Mellègue-Speicher hat ein weites Einzugsgebiet. Schadstoffe aus urbanen Abwässern, Düngemitteln und Metallen aus Tailings sind ein Bedrohung für die Wasserversorgung in Tunesien. Während der Trocken- und Regenzeit wurden vierzig Oberflächenwasserproben aus Gewässern und achtzehn aus dem Speicher entnommen. Am Fallbeispiel des Sarrat-Beckens wurden zudem Brunnenwasserproben analysiert, um Grundwasserbelastungen zu untersuchen. Die Gesamtgehalte an unedlen Metallen und Nährstoffen im Oberflächengewässer liegen nicht über internationalen Standards. Durch lösliche Evaporite, welche in den weiten Ausstrichbereichen triassischer Gesteine und in Tailings vorkommen, kann Blei sulfatisch gebunden werden. Andererseits besteht die Möglichkeit, dass Sulfat- und Chloridkomplexe die Löslichkeit einiger Metalle beeinflussen. Die Nährstoff- und Salzgehalte waren im Rmel-River, welchem Abwässer aus El Kef zufließen, am höchsten. Ein umgekehrter Metall-Konzentrationsgradient wurde in der Wassersäule des Wasserspeichers festgestellt. Zink, Blei und Aluminium waren im oberen Abschnitt angereichert, wohingegen Mangan, Eisen und Chrom in Richtung der Sediment-Wasser Grenze zunahmen. Das gleiche Verhalten wurde für Nitrat und Sauerstoff aufgrund von Metallfreisetzungen unter reduzierenden Bedingungen sowie der Lösung von Eisen- und Mangankolloiden im bodennahen Wasser beobachtet. Düngemittel und Abwässer sind vermutlich verantwortlich für die sehr hohen Nähstoffgehalte im Grundwasser.ResumenEl reservorio de 130 Mm3 de capacidad de Mellègue tiene una amplia cuenca. Los contaminantes incluyen las aguas residuales provenientes de distintas ciudades, fertilizantes de granjas y metales liberados desde colas de mina, y amenazan el suministro de agua de Túnez. Cuarenta muestras de agua superficial fueron colectadas desde cursos de agua y 18 desde el reservorio durante las estaciones secas y húmedas. Para evaluar la contaminación del agua subterránea, se consideró la cuenca Sarrat como un caso de estudio y se analizó el agua potable. Las cantidades totales de metales base y nutrientes en los cursos de agua no excedió los estándares internacionales. Las evaporitas en los grandes afloramientos triásicos y en las colas se disuelven y pueden fijar plomo como sulfatos; sin embargo, sulfato y cloruro pueden complejar e incrementar la solubilidad de algunos metales. Los contenidos en nutrientes y sales fueron máximos en el río Rmel que recibe aguas residuales desde el Kef. Un gradiente opuesto de metales fue observado en el agua del reservorio: elementos como Zn, Pb y Al se enriquecieron hacia la superficie mientras Mn, Fe y Cr se incrementaron hacia la interface sedimento-agua. El mismo comportamiento fue observado para NO3- y O2, debido a la liberación de metales bajo condiciones reductores en las aguas del fondo y la disolución de coloides de Fe y Mn. Los fertilizantes y las aguas residuales podrían ser los responsables por el nivel potencialmente peligroso de nutrientes en el agua subterránea.突尼斯西北部Mellegue流域水样及环境碱金属特征Mellegue水库汇水面积大,库容量达130×106m3。水体污染物主要源自城市废水、农用化肥、尾矿释放等,它们对突尼斯供水构成巨大威胁。分别在干、枯季从汇水河道取地表水样40个和水库水样18个;同时,为评价区域地下水污染状况,分析了Sarrat盆地泉水水样特征。河道水样的碱金属和养分含量未超国际水质标准。研究区内大面积三叠纪蒸发盐岩露头和尾矿露头发生溶解作用,铅被固定为硫酸盐,硫酸盐和氯化物混合作用进一步促进某些金属离子溶解。Rmel河因接受el Kef城市废水而养分和盐含量最高。水库水样呈现相反梯度变化:锌、铅和铝向上富集,而锰、铁和镉向底部水-岩界面富集。底水还原环境金属离子释放和铁锰胶体溶解作用使NO3-和O2含量具有相同变化规律。农用化肥和城市废水污染是地下水呈养分超标趋势的主要原因.
Like all other Mediterranean countries, Tunisia provides multiple examples of groundwater degrada... more Like all other Mediterranean countries, Tunisia provides multiple examples of groundwater degradation due to its overexploitation. This is especially the case in the Zeramdine-Mahdia-Jebeniana region (central east Tunisia), where recent measurements revealed an important piezometric drop in the Miocene aquifers. Through hydrodynamic and hydrochemical analysis, we studied the influence of the head decrease on groundwater flow and quality. The spatial and temporal analysis of the piezometry identified two totally independent compartments. This was confirmed by the hydrogeochemical and multivariate statistical analysis. The Miocene aquifer system was divided into two water groups: (1) the Zeramdine-Beni Hassen aquifer which is characterized by freshwater, Na-Ca-Cl-SO 4 facies, and salinity increase from west to east that is coinciding with the principal water flow direction; and (2) the Mahdia-Ksour Essef aquifer, which is defined throughout by high and heterogeneous salinity and Na-Cl...
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Papers by Fethi Lachaal