Learn about hydro chemical dynamics of Todos Santos aquifer, different types of use, and main conservation challenges. This collaborative research aimed to gain understanding on current and future state of seawater intrusion in the Todos Santos aquifer.
CSU Todos Santos is grateful to our local partners from CONAGUA-BCS who played an essential role in the development of this study.
Numerical model and Hydrochemical Analysis of the current and future state of seawater intrusion in the Todos Santos Aquifer.
The Todos Santos aquifer, Baja California Sur, Mexico, provides the sole source of freshwater to the town of Todos Santos, and is utilized for domestic and agricultural needs crucial to the town’s economy. The region is characterized by an arid climate. Major recharge to the aquifer is supplied from intermittent cyclones. Irregular and unpredictable recharge rates combined with population growth resulting from resort development put the Todos Santos aquifer at risk of overexploitation, causing potentially permanent water quality degradation by salinization as a result of seawater intrusion.
Understanding the complex response of seawater intrusion to variable pumping rates and sea-level rise is critical to water resource management in Todos Santos. This study utilized numerical simulation of variable-density groundwater flow, using SEAWAT, in conjunction with temporal and spatial hydrochemical analysis, to evaluate the current and future extent of seawater intrusion in the area. Forecasting simulations were run for five, ten, and twenty years following 2017, for five different hydrologic scenarios, which implemented various pumping rates, sea-level rise, and overexploitation of significant surface water resources.
Hydrochemical analysis shows an increase in groundwater specific conductance and chloride concentration within two kilometers of the coastline from 2007 to 2017. This combined with the distribution of groundwater samples exhibiting chloride concentration above the permissible limit for potable water (250 mg/L) suggest that the Todos Santos aquifer is experiencing effects of seawater intrusion up to 1.6 kilometers inland as of 2017. Analysis of groundwater cation exchange reactions indicates widening of the freshwater-seawater mixing zone from 2007 to 2017, further suggesting the exacerbation of seawater intrusion over this time span. Forecasting simulation results indicate that the extent of seawater intrusion is exacerbated by increased water withdrawal, overexploitation of surface water resources, the current rate of sea-level rise (~ 4 mm/yr), and an increased rate of sea-level rise of 25 mm/yr.
Related documents:
- Mahlknecht J, Sanford WE, Fichera M, Mora A. 2018. Freshwater-seawater transition in coastal Todos Santos aquifer, Baja California Sur. 5th International Conference on Energy and Environment Research, ICEER. Energy Procedia 153: 191-195.
- Marissa M. Fichera. 2019. Numerical modeling and Hydrochemical Analysis of the current and future state of seawater intrusion in the Todos Santos Aquifer, Mexico. Department of Geosciences, Colorado State University, Fort Collins, Colorado.
Contact the authors:
- William E. Sanford, Ph.D. — Associate Professor Department of Geosciences, Colorado State University
- Marissa M. Fichera, M.S.
Dynamics of major and trace elements during seawater intrusion in a coastal sedimentary aquifer impacted by anthropogenic activities
This study analyzed the dynamics of major ions and trace elements along the groundwater flow path of the coastal sedimentary Todos Santos aquifer in Baja California Sur, Mexico, moderately impacted by anthropogenic activities. The results indicate that the elements Ca2+, Mg2+, Ba2+, Sr2+ and Li+ are mobilized from the aquifer matrix during seawater intrusion, whereas the alkali-elements Na+, K+ and Rb+ are removed from solution, possibly due to cationic exchange process. The anions HCO3– and SO4 2− and the elements I and B are mobilized due to carbonate mineral weathering, whereas dissolved silica and the halides Br− and F− behave conservatively during salinization. Groundwater NO3 − is provided by sewage infiltration. Regarding trace elements behavior, we identify three groups: i) elements that are mobilized during saline intrusion (Fe, Co, V, Se, Re), ii) elements revealing low or no mobilization (Mo, Ni, Cr, Ta, W) and iii) elements that show an undefined tendency (U, As, Ge, Sb, Cu, Mn). The U and NO3 − levels in groundwater should be considered carefully because several wells have concentrations close to the permissible levels. This study may be useful as reference for knowing the possible effect of salinization in coastal aquifers under sea level rise scenarios driven by climate change.
Authors:
- Abraham Mora — Centro del Agua para América Latina y el Caribe, Escuela de ingeniería y Ciencias, Tecnológico de Monterrey, Campus Puebla, Puebla, Mexico
- Jürgen Mahlknecht — Centro del Agua para América Latina y el Caribe, Escuela de ingeniería y Ciencias, Tecnológico de Monterrey, Monterrey, Mexico
- Rogelio Ledesma-Ruiz — Centro del Agua para América Latina y el Caribe, Escuela de ingeniería y Ciencias, Tecnológico de Monterrey, Monterrey, Mexico
- William E. Sanford — Department of Geosciences, Colorado State University, Fort Collins, CO, USA
- Luis E. Lesser — Lesser y Asociados, S.A. de C.V., Queretaro, Mexico