Groundwater Flow Processes and Human Impact along the Arid US-Mexican Border, Evidenced by Environmental Tracers: The Case of Tecate, Baja California.

Jürgen Mahlknecht,Maria Esteller,Luis Daessle,Juan Torres-Martinez,Abrahan Mora

doi:10.3390/ijerph15050887

Abstract

With the increasing population, urbanization and industry in the arid area of Tecate, there is a concomitant increase in contaminants being introduced into the Tecate River and its aquifer. This contamination is damaging the usable groundwater supply and making local residents and commercial enterprises increasingly dependent on imported water from the Colorado River basin. In this study we apply a suite of chemical and isotopic tracers in order to evaluate groundwater flow and assess contamination trends. Groundwater recharge occurs through mountain-block and mountain-front recharge at higher elevations of the ranges. Groundwater from the unconfined, alluvial aquifer indicates recent recharge and little evolution. The increase in salinity along the flow path is due to interaction with weathering rock-forming silicate minerals and anthropogenic sources such as urban wastewater, residual solids and agricultural runoff from fertilizers, livestock manure and/or septic tanks and latrines. A spatial analysis shows local differences and the impact of the infiltration of imported waters from the Colorado River basin. The general trend of impaired water quality has scarcely been documented in the last decades, but it is expected to continue. Since the groundwater system is highly vulnerable, it is necessary to protect groundwater sources.

Highlights

The peninsula of Baja California in northwestern Mexico has few available water resources and is one of the most arid areas in Mexico
The higher values are found to the west (Tecate Valley) and to the extreme east (Rumorosa Valley) of the study area (Figure 1)
Human processes associated with urbanization, industry and agriculture have resulted in deterioration in the surface and groundwater quality in the arid Tecate area during the last several decades

Summary

Introduction

The peninsula of Baja California in northwestern Mexico has few available water resources and is one of the most arid areas in Mexico. The Tecate River is a sub-basin of the Tijuana River basin, a coastal watershed in Baja California adjacent to the USA-Mexico international border that discharges into the Pacific Ocean (Figure 1). In 2000, the groundwater resources provided about thirty percent of Tecate’s potable water supply [1], decreasing to only twenty percent in 2015 [2]. With the increase in population, urbanization, and industry in Tecate, there is a concomitant increase in contaminants being introduced into the Tecate River and groundwater resources. Res. Public Health 2018, 15, 887; doi:10.3390/ijerph15050887 www.mdpi.com/journal/ijerph

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Discussion

Conclusion