Rogelio Ledesma | Tecnológico de Monterrey (original) (raw)
Papers by Rogelio Ledesma
• A new multiple tracer approach for improved evaluation of nitrate sources and transformation pr... more • A new multiple tracer approach for improved evaluation of nitrate sources and transformation processes was developed. • Nitrate δ 15 N and δ 18 O isotopic compositions were completed with halide ratios. • Water isotopes were used to assess groundwater origin and recharge. • Groundwater chemical processes were evaluated using statistical approaches. • It is suggested that this approach is a powerful tool with potentially wide applications. a b s t r a c t Nitrate isotopic values are often used as a tool to understand sources of contamination in order to effectively manage groundwater quality. However, recent literature describes that biogeochemical reactions may modify these values. Therefore, data interpretation is difficult and often vague. We provide a discussion on this topic and complement the study using halides as comparative tracers assessing an aquifer underneath a sub-humid to humid region in NE Mexico. Hydrogeological information and stable water isotopes indicate that active groundwater recharge occurs in the 8000 km 2 study area under present-day climatic and hydrologic conditions. Nitrate isotopes and halide ratios indicate a diverse mix of nitrate sources and transformations. Nitrate sources include organic waste and wastewater, synthetic fertilizers and soil processes. Animal manure and sewage from septic tanks were the causes of groundwater nitrate pollution within orchards and vegetable agriculture. Dairy activities within a radius of 1000 m from a sampling point significantly contributed to nitrate pollution. Leachates from septic tanks caused nitrate pollution in residential areas. Soil nitrogen and animal waste were the sources of nitrate in groundwater under shrubland and grassland. Partial denitrification processes helped to attenuate nitrate concentration underneath agricultural lands and grassland, especially during summer months.
We used environmental tracers (CFCs, 18O, 2H, 3H, 14C, and water chemistry) to analyze the ground... more We used environmental tracers (CFCs, 18O, 2H, 3H, 14C, and water chemistry) to analyze the groundwater quality and flow system underlying and supplying part of the Metropolitan Area of Guadalajara, México. Most of the samples showed isotopic signatures, indicating recharge from local meteoric precipitation. Significant tritium concentrations were interpreted as a clear sign that groundwater was a mixture from water prior to 1952 and post 1960, which indicates that precipitation from the last years contributed significantly to groundwater recharge. CFCs revealed apparent recharge from 1960 to 1980. 14C results indicated groundwater aging approximately between 10,000 and 12,000 for the northern portion (Atemajac), and >20,000 years BP for the southern portion (Toluquilla). Comparison of CFCs, 3H and 14C concentrations proves that the samples are a mixture of waters from different ages. Additionally, zones with aquifer temperatures higher than 30°C were identified, suggesting the pr...
Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a su... more Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a sub-humid to humid climate adjacent to the Sierra Madre Oriental, this valley hosts an aquifer system that represents sequences of shales, marls, conglomerates, and alluvial deposits. Groundwater flows from mountainous recharge areas to the basin-fill deposits and provides base flows to supply drinking water to the adjacent metropolitan area of Monterrey. Recent studies examining the groundwater quality of the study area urge the mitigation of groundwater pollution. The objective of this study was to characterize the physical and chemical properties of the groundwater and to assess the processes controlling the groundwater's chemistry. Correlation was used to identify associations among various geochemical constituents. Factor analysis was applied to identify the water's chemical characteristics that were responsible for generating most of the variability within the dataset. Hierarchical cluster analysis was employed in combination with a post-hoc analysis of variance to partition the water samples into hydrochemical water groups: recharge waters (Ca-HCO 3 ), transition zone waters (Ca-HCO 3 -SO 4 to Ca-SO 4 -HCO 3 ) and discharge waters (Ca-SO 4 ). Inverse geochemical models of these groups were developed and constrained using PHREEQC to elucidate the chemical reactions controlling the water's chemistry between an initial (recharge) and final water. The primary reactions contributing to salinity were the following: (1) water-rock interactions, including the weathering of evaporitic rocks and dedolomitization; (2) dissolution of soil gas carbon dioxide; and (3) input from animal/human wastewater and manure in combination with by denitrification processes. Contributions from silicate weathering to salinity ranged from less important to insignificant. The findings suggest that it may not be cost-effective to regulate manure application to mitigate groundwater pollution.
Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a su... more Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a sub-humid to humid climate adjacent to the Sierra Madre Oriental, this valley hosts an aquifer system that represents sequences of shales, marls, conglomerates, and alluvial deposits. Groundwater flows from mountainous recharge areas to the basin-fill deposits and provides base flows to supply drinking water to the adjacent metropolitan area of Monterrey. Recent studies examining the groundwater quality of the study area urge the mitigation of groundwater pollution. The objective of this study was to characterize the physical and chemical properties of the groundwater and to assess the processes controlling the groundwater’s chemistry. Correlation was used to identify associations among various geochemical constituents. Factor analysis was applied to identify the water’s chemical characteristics that were responsible for generating most of he variability within the dataset. Hierarchical cluster analysis was employed in combination with a post-hoc analysis of variance to partition the water samples into hydrochemical water groups: recharge waters (CaHCO3), transition zone waters (Ca-HCO3-SO4 to Ca-SO4-HCO3) and discharge waters (CaSO4). Inverse geochemical models of these groups were developed and constrained using PHREEQC to elucidate the chemical reactions controlling the water’s chemistry between an initial (recharge) and final water. The primary reactions contributing to salinity were the following: (1) water-rock interactions, including the weathering of evaporitic rocks and dedolomitization; (2) dissolution of soil gas carbon dioxide; and (3) input from animal/human wastewater and manure in combination with by denitrification processes. Contributions from silicate weathering to salinity ranged from less important to insignificant. The findings suggest that it may not be cost-effective to regulate manure application to mitigate groundwater pollution.
• A new multiple tracer approach for improved evaluation of nitrate sources and transformation pr... more • A new multiple tracer approach for improved evaluation of nitrate sources and transformation processes was developed. • Nitrate δ 15 N and δ 18 O isotopic compositions were completed with halide ratios. • Water isotopes were used to assess groundwater origin and recharge. • Groundwater chemical processes were evaluated using statistical approaches. • It is suggested that this approach is a powerful tool with potentially wide applications. a b s t r a c t Nitrate isotopic values are often used as a tool to understand sources of contamination in order to effectively manage groundwater quality. However, recent literature describes that biogeochemical reactions may modify these values. Therefore, data interpretation is difficult and often vague. We provide a discussion on this topic and complement the study using halides as comparative tracers assessing an aquifer underneath a sub-humid to humid region in NE Mexico. Hydrogeological information and stable water isotopes indicate that active groundwater recharge occurs in the 8000 km 2 study area under present-day climatic and hydrologic conditions. Nitrate isotopes and halide ratios indicate a diverse mix of nitrate sources and transformations. Nitrate sources include organic waste and wastewater, synthetic fertilizers and soil processes. Animal manure and sewage from septic tanks were the causes of groundwater nitrate pollution within orchards and vegetable agriculture. Dairy activities within a radius of 1000 m from a sampling point significantly contributed to nitrate pollution. Leachates from septic tanks caused nitrate pollution in residential areas. Soil nitrogen and animal waste were the sources of nitrate in groundwater under shrubland and grassland. Partial denitrification processes helped to attenuate nitrate concentration underneath agricultural lands and grassland, especially during summer months.
We used environmental tracers (CFCs, 18O, 2H, 3H, 14C, and water chemistry) to analyze the ground... more We used environmental tracers (CFCs, 18O, 2H, 3H, 14C, and water chemistry) to analyze the groundwater quality and flow system underlying and supplying part of the Metropolitan Area of Guadalajara, México. Most of the samples showed isotopic signatures, indicating recharge from local meteoric precipitation. Significant tritium concentrations were interpreted as a clear sign that groundwater was a mixture from water prior to 1952 and post 1960, which indicates that precipitation from the last years contributed significantly to groundwater recharge. CFCs revealed apparent recharge from 1960 to 1980. 14C results indicated groundwater aging approximately between 10,000 and 12,000 for the northern portion (Atemajac), and >20,000 years BP for the southern portion (Toluquilla). Comparison of CFCs, 3H and 14C concentrations proves that the samples are a mixture of waters from different ages. Additionally, zones with aquifer temperatures higher than 30°C were identified, suggesting the pr...
Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a su... more Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a sub-humid to humid climate adjacent to the Sierra Madre Oriental, this valley hosts an aquifer system that represents sequences of shales, marls, conglomerates, and alluvial deposits. Groundwater flows from mountainous recharge areas to the basin-fill deposits and provides base flows to supply drinking water to the adjacent metropolitan area of Monterrey. Recent studies examining the groundwater quality of the study area urge the mitigation of groundwater pollution. The objective of this study was to characterize the physical and chemical properties of the groundwater and to assess the processes controlling the groundwater's chemistry. Correlation was used to identify associations among various geochemical constituents. Factor analysis was applied to identify the water's chemical characteristics that were responsible for generating most of the variability within the dataset. Hierarchical cluster analysis was employed in combination with a post-hoc analysis of variance to partition the water samples into hydrochemical water groups: recharge waters (Ca-HCO 3 ), transition zone waters (Ca-HCO 3 -SO 4 to Ca-SO 4 -HCO 3 ) and discharge waters (Ca-SO 4 ). Inverse geochemical models of these groups were developed and constrained using PHREEQC to elucidate the chemical reactions controlling the water's chemistry between an initial (recharge) and final water. The primary reactions contributing to salinity were the following: (1) water-rock interactions, including the weathering of evaporitic rocks and dedolomitization; (2) dissolution of soil gas carbon dioxide; and (3) input from animal/human wastewater and manure in combination with by denitrification processes. Contributions from silicate weathering to salinity ranged from less important to insignificant. The findings suggest that it may not be cost-effective to regulate manure application to mitigate groundwater pollution.
Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a su... more Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a sub-humid to humid climate adjacent to the Sierra Madre Oriental, this valley hosts an aquifer system that represents sequences of shales, marls, conglomerates, and alluvial deposits. Groundwater flows from mountainous recharge areas to the basin-fill deposits and provides base flows to supply drinking water to the adjacent metropolitan area of Monterrey. Recent studies examining the groundwater quality of the study area urge the mitigation of groundwater pollution. The objective of this study was to characterize the physical and chemical properties of the groundwater and to assess the processes controlling the groundwater’s chemistry. Correlation was used to identify associations among various geochemical constituents. Factor analysis was applied to identify the water’s chemical characteristics that were responsible for generating most of he variability within the dataset. Hierarchical cluster analysis was employed in combination with a post-hoc analysis of variance to partition the water samples into hydrochemical water groups: recharge waters (CaHCO3), transition zone waters (Ca-HCO3-SO4 to Ca-SO4-HCO3) and discharge waters (CaSO4). Inverse geochemical models of these groups were developed and constrained using PHREEQC to elucidate the chemical reactions controlling the water’s chemistry between an initial (recharge) and final water. The primary reactions contributing to salinity were the following: (1) water-rock interactions, including the weathering of evaporitic rocks and dedolomitization; (2) dissolution of soil gas carbon dioxide; and (3) input from animal/human wastewater and manure in combination with by denitrification processes. Contributions from silicate weathering to salinity ranged from less important to insignificant. The findings suggest that it may not be cost-effective to regulate manure application to mitigate groundwater pollution.