Degradation of water quality in the Todos Santos, Mexico, coastal aquifer and loss of groundwater inflow to the La Poza estuary
Abstract
The Todos Santos aquifer is the main source of water for the small coastal community of Todos Santos, Baja California Sur, Mexico and for the surrounding agricultural areas. The aquifer also provides a source of fresh water to a small estuary (La Poza) along the Pacific coast. The region is characterized by prolonged droughts interrupted by abrupt storms, mainly in the form of intermittent cyclones during summer months. The mean annual precipitation is 150 mm. With planned development, there are concerns of detrimental effects on the quantity and quality of groundwater and the potential effects on La Poza. Presented here are the preliminary results of an investigation into the water chemistry and stable isotope composition of both groundwater and water in the estuary. Water chemistry from 2017 is compared to the chemistry from 2007 to determine if there are changes to quality pre-development.
The results of the chemical analysis performed on groundwater samples collected in 21 wells located along the aquifer gradient show that water becomes more mineralized along its flowpath, with the most mineralized water located along the coastline, suggesting seawater intrusion. Along the coast, groundwater interacts with seawater and undergoes evaporation simultaneously, with water in the estuary having salinity beyond seawater composition. Salinity values in the wells near the coast show a significant increase in value since 2007. Stable isotope composition of groundwater is very depleted, indicating that recharge occurs mainly during heavy rains. Some groundwater shows evaporative enrichment. The isotope composition of the estuary is much more enriched and indicates that the water is evaporated sea water, suggesting minimal current input of fresh groundwater. Air photos show a decrease in the area of La Poza since 2007. Combined with the results of the chemical and isotope analyses of the estuary, it is believed that there has been an increase in groundwater withdrawal from wells approaching the coastline, decreasing the groundwater input to La Poza. Increase in water withdrawals and sea level rise will further degrade the estuary and groundwater quality.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.H13L1915S
- Keywords:
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- 1830 Groundwater/surface water interaction;
- HYDROLOGYDE: 1890 Wetlands;
- HYDROLOGYDE: 4217 Coastal processes;
- OCEANOGRAPHY: GENERALDE: 4235 Estuarine processes;
- OCEANOGRAPHY: GENERAL