The Kandi basin is located in northeast Benin (West Africa). This study is focused on the estimation of water fluxes exchanged between the river Niger (and its tributaries) and the transboundary Iullemeden Aquifer Sys...The Kandi basin is located in northeast Benin (West Africa). This study is focused on the estimation of water fluxes exchanged between the river Niger (and its tributaries) and the transboundary Iullemeden Aquifer System. In that framework, an innovative approach based on the application of the Bayesian Mixing Model (MixSIAR) analysis on water isotopes (oxygen-18, deuterium and tritium) was performed. Moreover, to assess the relevance of the model outputs, Pearson’s correlation and Principal Component Analysis (PCA) have been done. A complex relationship between surface water and groundwater has been found. Sixty percent (60%) of groundwater samples are made of more than 70% river water and rainwater;while 31.25% of surface water samples are made of about 84% groundwater. To safeguard sustainable water resources for the well-being of the local communities, surface water and groundwater must be managed as a unique component in the Kandi basin.展开更多
Introduction: Pregnancy, childbirth, and their consequences continue to be the leading cause of death, illness, and disability among women of reproductive age in developing countries. In Niger, maternal deaths account...Introduction: Pregnancy, childbirth, and their consequences continue to be the leading cause of death, illness, and disability among women of reproductive age in developing countries. In Niger, maternal deaths account for about 39% of all deaths of women aged 15-49. Our aim was to identify the factors linked to maternal mortality in order to contribute to its reduction. Method: this is a descriptive retrospective study of 379 cases of maternal deaths collected at the Maradi CSME from January 1, 2018, to December 31, 2021.Results: Our study’s maternal mortality ratio is 2645.72 per 100,000 live births. The mean age of our patients was 27.46 years, with extremes ranging from 15 to 47 years. The 20-24 age group was the most represented, with 88 cases (23.2%). Housewives were 361 (95.3%), and 334 patients (88.1%) were uneducated. There were 261 of them from rural areas, i.e. 69%. The mean parity in our study was 3.46, with extremes ranging from 0 to 15. Multiparous patients 117 cases (30.9%) represented the most significant proportion. Only 42 patients (11.08%) had performed four or more antenatal consultations. Direct obstetric causes accounted for 56.73% of the causes of maternal death. Anemia was the leading cause of maternal death (31.66%). Nearly half of the patients had died before 24 hours after admission, i.e. 49.86%. Conclusion: Maternal mortality remains a significant challenge for developing countries, given its magnitude and timid decline. The fight to reduce maternal mortality must be the priority of our countries’ health policies.展开更多
Introduction: Emergency obstetric hysterectomy (EOH) is a lifesaving procedure that is performed as a last resort in cases of severe postpartum haemorrhage. Objective: The objective of this study was to determine the ...Introduction: Emergency obstetric hysterectomy (EOH) is a lifesaving procedure that is performed as a last resort in cases of severe postpartum haemorrhage. Objective: The objective of this study was to determine the incidence, socio-demographic profile of patients, indications, management and maternal-fetal outcomes of EOH in a maternity hospital with limited resources in Niger. Methodology: This was an eight-year retrospective cohort study involving the analysis of medical records from patients who underwent emergency obstetric hysterectomies between 1 January 2015 and 31 December 2022 at the Mother and Child Health Centre (MCHC) in Maradi, Niger. The epidemiological data, indications, and outcomes of EOH were collated and subjected to analysis using the statistical software package SPSS 21.0. Comparisons were made using the Chi-squared test. A p-value of less than 0.05 was considered statistically significant. Results: During the study period, 239 cases of emergency obstetric hysterectomy were recorded out of 269,710 deliveries, representing a frequency of 0.89%. The mean age of the patients was 32.41 years (range: 17 - 50 years). The patients were identified as married (239 cases, 100%), unemployed (228 cases, 95.4%), and not attending school (215 cases, 90%). The largest number of cases were observed in large multiparous women (i.e., those with more than five children), representing 58.6% of the total number of cases (140 patients). The average parity among this group was 6.15 children. The majority of patients (229 patients, 95.82%) had undergone in utero transfer, with 169 patients (70.71%), originating from peripheral maternity units in the Maradi region. Upon admission, 116 patients (48.53%) exhibited active genital haemorrhage, while 58 patients (24.26%) were in shock. The primary indications for hysterectomy were uterine rupture (153 patients, 64%), uterine atony (77 patients, 32.2%), and placental accreta (six patients, 2.5%). Hysterectomy was performed by an obstetric gynaecologist (230 patients, 96.2%), an obstetric gynaecology resident (six patients, 2.5%), or a general practitioner with district surgical expertise (three patients, 1.3%). In the majority of cases (180 patients, 75.3%), total hysterectomy was performed. The incidence of maternal mortality (26 patients, 10.9%), and perinatal mortality (223 newborns, 93.4%) was notably elevated in our series. Conclusion: Our findings are in close alignment with those previously documented in the literature. The practice of emergency obstetric hysterectomy is a common occurrence in our region. It is considered a last resort when conservative procedures have failed or are not an option. Improved obstetric management would result in a reduction in the number of cases of haemostatic hysterectomy. The availability of blood products is expected to improve maternal prognosis.展开更多
The coastal sedimentary basin in southern Benin consists of monoclinal layers divided into two plateau zones (North and South) which are separated by a longitudinal depression ESE-WNW. The valleys of the main N-S-orie...The coastal sedimentary basin in southern Benin consists of monoclinal layers divided into two plateau zones (North and South) which are separated by a longitudinal depression ESE-WNW. The valleys of the main N-S-oriented rivers (Ouémé, Couffo and Mono) set the bondaries of the different plateau of the BSC (Coastal Sedimentary Basin). The present study, based on geology, hydrochemistry, temperature and log data available on boreholes, makes a physico-chemical characterization of the waters of the gushing aquifers of the coastal sedimentary basin of Benin. The gushing water boreholes are shared between the valleys of the main rivers of the BSC. Some of these boreholes are </span><span style="font-family:Verdana;">thermal with a water temperature between 38 and 69 degrees Celsius. The</span><span style="font-family:Verdana;"> hydrogeological correlations established in the BSC in accordance to the North-</span></span></span><span><span><span style="font-family:""> </span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">South direction in the valleys of the main streams (Couffo and Ouémé) reveal that the captured aquifers are sands, marls and limestones that respond either </span><span style="font-family:Verdana;">in major discordance (northern zone) or above the sedimentation gaps</span><span style="font-family:Verdana;"> (southern zone). Chemical analyses have shown that gushing thermal waters are mineralized in the south with a neutral to basic pH and are highly concentrated with bicarbonate, calcium and magnesium ions. In the North, on the other hand, thermal waters are acidic with a pH ranging from 4.8 to 5.9. The acidic nature of the northern waters is influenced by the crystalline base while the southern neutral to basic waters are influenced by the lithological nature (limestone and marl) of the aquifer. The random distribution of thermal water boreholes in the valleys of the main BSC streams is believed to be related to tectonic events.展开更多
In southern Benin, where population is growing and water demand for domestic activities is increasing, water balance assessment constitutes a serious concern about sustainability of water resources. Major ions have be...In southern Benin, where population is growing and water demand for domestic activities is increasing, water balance assessment constitutes a serious concern about sustainability of water resources. Major ions have been employed with statistical methods to identify geochemical processes controlling groundwater quality. Multivariate statistical analysis (principal component analysis “PCA” and hierarchical cluster analysis “HCA”) revealed the main sources of groundwater mineralization. According to the hydrochemical data and the methods of treatment, groundwater mineralization in the investigated aquifer is caused by four main processes: 1) mixing with Nokoué lake and Porto-Novo lagoon salt water causing salinity to increase in the southern part of the aquifer;2) anthropogenic activities;3) cation exchange process;and 4) soil CO2 diffusion providing a large proportion of bicarbonates.展开更多
Water is indispensable at life. Resources in waters of the township of Abomey-Calavi are of national importance. The township of Abomey-Calavi is very close to the biggest plan of water Beninese lagoon: The Nokoué...Water is indispensable at life. Resources in waters of the township of Abomey-Calavi are of national importance. The township of Abomey-Calavi is very close to the biggest plan of water Beninese lagoon: The Nokoué lake. Besides, not only the waters of the ground water are consumed by the majority of the population from the traditional well, but also, the underground waters of the terminal continnental of the township of Abomey-Calavi are exploited intensely by the Society Nationnale of the Waters of Benin (SONEB) to nourish in drinking water in the townships of Abomey-Calavi, of Cotonou the biggest city of the country and Sèmè. The microbiological parameter followup (total coliforms, coliforms thermotolerants and enterrococcis) to the level of many traditional well and deep boring and some different points of Nokoué lake were the object of a treatment of data by the establishment of card of fecal contamination of waters natural of the region, that informs us on the quality of waters by the slant of a microbiological quality indication that calculates itself according to the method of Bovesse and Depelchin (1980). The survey of the microbiological contamination indication, succeeds to the establishment of seasonal cards of quality of waters.展开更多
The objective of this research is to determine the physicochemical elements contained in the groundwater and in the deposits originating from these waters of the Arrondissement of Dêkin, Commune of Dangbo in the ...The objective of this research is to determine the physicochemical elements contained in the groundwater and in the deposits originating from these waters of the Arrondissement of Dêkin, Commune of Dangbo in the South of Benin. Physical parameters were measured from the multi-parameter and the chemical parameters by reagent assays. The precipitate from the groundwater was studied by speciation. The different assays were carried out using the Hach Lange DR2800 Spectrophotometer. The data processing was done with different software including ArcGis 10.1, Diagram.Ink of Roland SIMLER and PHREEQC 2.17.4137. Strong mineralization of the deposit from the drilling water was indicated in these three elements: Copper (220.1 mg/kg), iron (2528 mg/kg) and zinc (239.5 mg/kg) whose contents are higher than the French guideline values for heavy metal content in sediments in mg/kg. The calculation of the Saturation Indices of the drilling water shows saturation with respect to Goethite and Hematite. All these results have led us to conclude that the high content of Metallic Trace Element (MTE) in the deposit and especially of the iron in the drilling water originates from the dissolution-precipitation of the aquifer rock.展开更多
The objective of this study is to reveal the negative impacts of the practices of acadjas on the Aheme lake in Benin. Various material and methods were used for the measures of the physicochemical parameters such as: ...The objective of this study is to reveal the negative impacts of the practices of acadjas on the Aheme lake in Benin. Various material and methods were used for the measures of the physicochemical parameters such as: colorimetric HACH DR/890, the multiparameter WTW 340i and specific kits for the dosage of minerals. Also, the investigations were made with the resources by persons. It emerges from this study that the practices of acadjas asphyxiate and disturb the lake species. In fact, the concentrations in dissolved oxygen became very weak (1595 mg/L to 3740 mg/L), and the contents of nitrites (2, 25 mg/L to 14, 5 mg/L), suspension materials and turbidity are raised. The consequences both on the aquatic fauna and on the vegetation of the bank are worrying. The waterside populations are also threatened. Some actions in an attempt to regulate the practice of acadjas and promote reforestation of the lagoon bank need to be put in place.展开更多
The knowledge about groundwater flow conditions within Volta river basin in Benin, has restricted information coming to piezometry, water storage time, water path, and water quality. A good groundwater resources asses...The knowledge about groundwater flow conditions within Volta river basin in Benin, has restricted information coming to piezometry, water storage time, water path, and water quality. A good groundwater resources assessment of this sudano-sahelian area, is a huge condition for the sustainable management of water resources, which since the part of the 20th century is facing a severe drought that leads to a greater aridity. This article provides a summary with the main elements of carbon isotope (13C and 14C) as well as tritium (3H) coupled with hydrogeological and hydrochemical data. The goal is to improve the initial water recharging and the groundwater flow system within the aquifer. Two main results can be produced from the groundwater chemistry. First, the interactions between groundwater and clay minerals related to the residence time of groundwater are indicated by a slight evolution of Ca-HCO3 and Ca-Mg-HCO3 to Na-HCO3. Beside that towards water types Cl-NO3 indicates the anthropogenic influence on groundwater, related to agricultural activities and sanitation conditions. The carbon-14 activity measured on the TDIC is between 17.29 and 85.47 pmC. Therefore, it contains some samples covering a wide period of time from now to the Holocene implying a continuous system recharging over time. All the data confirm the assumption of a homogeneous, largely unified aquifer system with a multi-layer structure, but it also points out the low resource sustainability and a strong anthropogenic contamination of the most superficial horizons.展开更多
The Miocene-Pliocene aquifer of Benin’s Coastal Sedimentary Basin(BSC)is the most heavily exploited aquifer for supplying water to the cities of Cotonou,Porto-Novo,and their surrounding areas,thanks to two catchment ...The Miocene-Pliocene aquifer of Benin’s Coastal Sedimentary Basin(BSC)is the most heavily exploited aquifer for supplying water to the cities of Cotonou,Porto-Novo,and their surrounding areas,thanks to two catchment fields located on the Sakete and Allada plateaus.This study,which focuses on the Sakete plateau,aims to improve knowledge of the geometry of this part of the aquifer shared with Nigeria.Inhabited by a high population density with varied economic activities,this aquifer is subject to excessive withdrawal and deterioration in water quality.Furthermore,in this part of Benin,there has been a spectacular proliferation of private wells and boreholes,often referred to as private autonomous water stations.This situation of unregulated exploitation puts further pressure on the aquifer and thus compromises the sustainable exploitation of water resources already subject to the effects of climate change.It is therefore necessary to investigate and deepen our knowledge of its geometry in order to better understand the system.In order to refine the wall and edges of the aquifer’s geometry,32 geophysical surveys were carried out along three well-defined transects,using the Time Domain Electromagnetic(TDEM)method.This method,known for its flexibility in identifying conductive soils such as clays,confirmed that the aquifer is multi-layered,interspersed with clay lenses of varying thickness in places.The aquifer wall,consisting of clay,is estimated to be between 50 and 100 m deep at the northern edge of the plateau near the Lama depression,with an outcrop of the clay layer towards Nigeria on the same cross-section.On the western profile,the wall is located between 90 and 120 m depending on the site,while on the southern profile of the plateau,the depth of the wall is almost constant at 80 m and deepens(110 m)towards the Nigerian border in the east.The Feflow numerical code was used for a finite element mesh of the aquifer.The continuous super mesh is characterized by 193,864 nodes,272,892 prism-triangle elements with 06 nodes per element.527 borehole logs and TDEM surveys were used in conjunction to establish a conceptual model of the three-dimensional geometry.展开更多
文摘The Kandi basin is located in northeast Benin (West Africa). This study is focused on the estimation of water fluxes exchanged between the river Niger (and its tributaries) and the transboundary Iullemeden Aquifer System. In that framework, an innovative approach based on the application of the Bayesian Mixing Model (MixSIAR) analysis on water isotopes (oxygen-18, deuterium and tritium) was performed. Moreover, to assess the relevance of the model outputs, Pearson’s correlation and Principal Component Analysis (PCA) have been done. A complex relationship between surface water and groundwater has been found. Sixty percent (60%) of groundwater samples are made of more than 70% river water and rainwater;while 31.25% of surface water samples are made of about 84% groundwater. To safeguard sustainable water resources for the well-being of the local communities, surface water and groundwater must be managed as a unique component in the Kandi basin.
文摘Introduction: Pregnancy, childbirth, and their consequences continue to be the leading cause of death, illness, and disability among women of reproductive age in developing countries. In Niger, maternal deaths account for about 39% of all deaths of women aged 15-49. Our aim was to identify the factors linked to maternal mortality in order to contribute to its reduction. Method: this is a descriptive retrospective study of 379 cases of maternal deaths collected at the Maradi CSME from January 1, 2018, to December 31, 2021.Results: Our study’s maternal mortality ratio is 2645.72 per 100,000 live births. The mean age of our patients was 27.46 years, with extremes ranging from 15 to 47 years. The 20-24 age group was the most represented, with 88 cases (23.2%). Housewives were 361 (95.3%), and 334 patients (88.1%) were uneducated. There were 261 of them from rural areas, i.e. 69%. The mean parity in our study was 3.46, with extremes ranging from 0 to 15. Multiparous patients 117 cases (30.9%) represented the most significant proportion. Only 42 patients (11.08%) had performed four or more antenatal consultations. Direct obstetric causes accounted for 56.73% of the causes of maternal death. Anemia was the leading cause of maternal death (31.66%). Nearly half of the patients had died before 24 hours after admission, i.e. 49.86%. Conclusion: Maternal mortality remains a significant challenge for developing countries, given its magnitude and timid decline. The fight to reduce maternal mortality must be the priority of our countries’ health policies.
文摘Introduction: Emergency obstetric hysterectomy (EOH) is a lifesaving procedure that is performed as a last resort in cases of severe postpartum haemorrhage. Objective: The objective of this study was to determine the incidence, socio-demographic profile of patients, indications, management and maternal-fetal outcomes of EOH in a maternity hospital with limited resources in Niger. Methodology: This was an eight-year retrospective cohort study involving the analysis of medical records from patients who underwent emergency obstetric hysterectomies between 1 January 2015 and 31 December 2022 at the Mother and Child Health Centre (MCHC) in Maradi, Niger. The epidemiological data, indications, and outcomes of EOH were collated and subjected to analysis using the statistical software package SPSS 21.0. Comparisons were made using the Chi-squared test. A p-value of less than 0.05 was considered statistically significant. Results: During the study period, 239 cases of emergency obstetric hysterectomy were recorded out of 269,710 deliveries, representing a frequency of 0.89%. The mean age of the patients was 32.41 years (range: 17 - 50 years). The patients were identified as married (239 cases, 100%), unemployed (228 cases, 95.4%), and not attending school (215 cases, 90%). The largest number of cases were observed in large multiparous women (i.e., those with more than five children), representing 58.6% of the total number of cases (140 patients). The average parity among this group was 6.15 children. The majority of patients (229 patients, 95.82%) had undergone in utero transfer, with 169 patients (70.71%), originating from peripheral maternity units in the Maradi region. Upon admission, 116 patients (48.53%) exhibited active genital haemorrhage, while 58 patients (24.26%) were in shock. The primary indications for hysterectomy were uterine rupture (153 patients, 64%), uterine atony (77 patients, 32.2%), and placental accreta (six patients, 2.5%). Hysterectomy was performed by an obstetric gynaecologist (230 patients, 96.2%), an obstetric gynaecology resident (six patients, 2.5%), or a general practitioner with district surgical expertise (three patients, 1.3%). In the majority of cases (180 patients, 75.3%), total hysterectomy was performed. The incidence of maternal mortality (26 patients, 10.9%), and perinatal mortality (223 newborns, 93.4%) was notably elevated in our series. Conclusion: Our findings are in close alignment with those previously documented in the literature. The practice of emergency obstetric hysterectomy is a common occurrence in our region. It is considered a last resort when conservative procedures have failed or are not an option. Improved obstetric management would result in a reduction in the number of cases of haemostatic hysterectomy. The availability of blood products is expected to improve maternal prognosis.
文摘The coastal sedimentary basin in southern Benin consists of monoclinal layers divided into two plateau zones (North and South) which are separated by a longitudinal depression ESE-WNW. The valleys of the main N-S-oriented rivers (Ouémé, Couffo and Mono) set the bondaries of the different plateau of the BSC (Coastal Sedimentary Basin). The present study, based on geology, hydrochemistry, temperature and log data available on boreholes, makes a physico-chemical characterization of the waters of the gushing aquifers of the coastal sedimentary basin of Benin. The gushing water boreholes are shared between the valleys of the main rivers of the BSC. Some of these boreholes are </span><span style="font-family:Verdana;">thermal with a water temperature between 38 and 69 degrees Celsius. The</span><span style="font-family:Verdana;"> hydrogeological correlations established in the BSC in accordance to the North-</span></span></span><span><span><span style="font-family:""> </span></span></span><span><span><span style="font-family:""><span style="font-family:Verdana;">South direction in the valleys of the main streams (Couffo and Ouémé) reveal that the captured aquifers are sands, marls and limestones that respond either </span><span style="font-family:Verdana;">in major discordance (northern zone) or above the sedimentation gaps</span><span style="font-family:Verdana;"> (southern zone). Chemical analyses have shown that gushing thermal waters are mineralized in the south with a neutral to basic pH and are highly concentrated with bicarbonate, calcium and magnesium ions. In the North, on the other hand, thermal waters are acidic with a pH ranging from 4.8 to 5.9. The acidic nature of the northern waters is influenced by the crystalline base while the southern neutral to basic waters are influenced by the lithological nature (limestone and marl) of the aquifer. The random distribution of thermal water boreholes in the valleys of the main BSC streams is believed to be related to tectonic events.
文摘In southern Benin, where population is growing and water demand for domestic activities is increasing, water balance assessment constitutes a serious concern about sustainability of water resources. Major ions have been employed with statistical methods to identify geochemical processes controlling groundwater quality. Multivariate statistical analysis (principal component analysis “PCA” and hierarchical cluster analysis “HCA”) revealed the main sources of groundwater mineralization. According to the hydrochemical data and the methods of treatment, groundwater mineralization in the investigated aquifer is caused by four main processes: 1) mixing with Nokoué lake and Porto-Novo lagoon salt water causing salinity to increase in the southern part of the aquifer;2) anthropogenic activities;3) cation exchange process;and 4) soil CO2 diffusion providing a large proportion of bicarbonates.
文摘Water is indispensable at life. Resources in waters of the township of Abomey-Calavi are of national importance. The township of Abomey-Calavi is very close to the biggest plan of water Beninese lagoon: The Nokoué lake. Besides, not only the waters of the ground water are consumed by the majority of the population from the traditional well, but also, the underground waters of the terminal continnental of the township of Abomey-Calavi are exploited intensely by the Society Nationnale of the Waters of Benin (SONEB) to nourish in drinking water in the townships of Abomey-Calavi, of Cotonou the biggest city of the country and Sèmè. The microbiological parameter followup (total coliforms, coliforms thermotolerants and enterrococcis) to the level of many traditional well and deep boring and some different points of Nokoué lake were the object of a treatment of data by the establishment of card of fecal contamination of waters natural of the region, that informs us on the quality of waters by the slant of a microbiological quality indication that calculates itself according to the method of Bovesse and Depelchin (1980). The survey of the microbiological contamination indication, succeeds to the establishment of seasonal cards of quality of waters.
文摘The objective of this research is to determine the physicochemical elements contained in the groundwater and in the deposits originating from these waters of the Arrondissement of Dêkin, Commune of Dangbo in the South of Benin. Physical parameters were measured from the multi-parameter and the chemical parameters by reagent assays. The precipitate from the groundwater was studied by speciation. The different assays were carried out using the Hach Lange DR2800 Spectrophotometer. The data processing was done with different software including ArcGis 10.1, Diagram.Ink of Roland SIMLER and PHREEQC 2.17.4137. Strong mineralization of the deposit from the drilling water was indicated in these three elements: Copper (220.1 mg/kg), iron (2528 mg/kg) and zinc (239.5 mg/kg) whose contents are higher than the French guideline values for heavy metal content in sediments in mg/kg. The calculation of the Saturation Indices of the drilling water shows saturation with respect to Goethite and Hematite. All these results have led us to conclude that the high content of Metallic Trace Element (MTE) in the deposit and especially of the iron in the drilling water originates from the dissolution-precipitation of the aquifer rock.
文摘The objective of this study is to reveal the negative impacts of the practices of acadjas on the Aheme lake in Benin. Various material and methods were used for the measures of the physicochemical parameters such as: colorimetric HACH DR/890, the multiparameter WTW 340i and specific kits for the dosage of minerals. Also, the investigations were made with the resources by persons. It emerges from this study that the practices of acadjas asphyxiate and disturb the lake species. In fact, the concentrations in dissolved oxygen became very weak (1595 mg/L to 3740 mg/L), and the contents of nitrites (2, 25 mg/L to 14, 5 mg/L), suspension materials and turbidity are raised. The consequences both on the aquatic fauna and on the vegetation of the bank are worrying. The waterside populations are also threatened. Some actions in an attempt to regulate the practice of acadjas and promote reforestation of the lagoon bank need to be put in place.
基金the framework of the International Atomic Energy Agency(IAEA)Regional Project RAF-7011,Vienna,Austria
文摘The knowledge about groundwater flow conditions within Volta river basin in Benin, has restricted information coming to piezometry, water storage time, water path, and water quality. A good groundwater resources assessment of this sudano-sahelian area, is a huge condition for the sustainable management of water resources, which since the part of the 20th century is facing a severe drought that leads to a greater aridity. This article provides a summary with the main elements of carbon isotope (13C and 14C) as well as tritium (3H) coupled with hydrogeological and hydrochemical data. The goal is to improve the initial water recharging and the groundwater flow system within the aquifer. Two main results can be produced from the groundwater chemistry. First, the interactions between groundwater and clay minerals related to the residence time of groundwater are indicated by a slight evolution of Ca-HCO3 and Ca-Mg-HCO3 to Na-HCO3. Beside that towards water types Cl-NO3 indicates the anthropogenic influence on groundwater, related to agricultural activities and sanitation conditions. The carbon-14 activity measured on the TDIC is between 17.29 and 85.47 pmC. Therefore, it contains some samples covering a wide period of time from now to the Holocene implying a continuous system recharging over time. All the data confirm the assumption of a homogeneous, largely unified aquifer system with a multi-layer structure, but it also points out the low resource sustainability and a strong anthropogenic contamination of the most superficial horizons.
文摘The Miocene-Pliocene aquifer of Benin’s Coastal Sedimentary Basin(BSC)is the most heavily exploited aquifer for supplying water to the cities of Cotonou,Porto-Novo,and their surrounding areas,thanks to two catchment fields located on the Sakete and Allada plateaus.This study,which focuses on the Sakete plateau,aims to improve knowledge of the geometry of this part of the aquifer shared with Nigeria.Inhabited by a high population density with varied economic activities,this aquifer is subject to excessive withdrawal and deterioration in water quality.Furthermore,in this part of Benin,there has been a spectacular proliferation of private wells and boreholes,often referred to as private autonomous water stations.This situation of unregulated exploitation puts further pressure on the aquifer and thus compromises the sustainable exploitation of water resources already subject to the effects of climate change.It is therefore necessary to investigate and deepen our knowledge of its geometry in order to better understand the system.In order to refine the wall and edges of the aquifer’s geometry,32 geophysical surveys were carried out along three well-defined transects,using the Time Domain Electromagnetic(TDEM)method.This method,known for its flexibility in identifying conductive soils such as clays,confirmed that the aquifer is multi-layered,interspersed with clay lenses of varying thickness in places.The aquifer wall,consisting of clay,is estimated to be between 50 and 100 m deep at the northern edge of the plateau near the Lama depression,with an outcrop of the clay layer towards Nigeria on the same cross-section.On the western profile,the wall is located between 90 and 120 m depending on the site,while on the southern profile of the plateau,the depth of the wall is almost constant at 80 m and deepens(110 m)towards the Nigerian border in the east.The Feflow numerical code was used for a finite element mesh of the aquifer.The continuous super mesh is characterized by 193,864 nodes,272,892 prism-triangle elements with 06 nodes per element.527 borehole logs and TDEM surveys were used in conjunction to establish a conceptual model of the three-dimensional geometry.
