Climate change could taint aquifers with seawater, JPL finds

The groundwater in Southern California and most other coastal areas will likely be tainted by saltwater as sea levels rise due to climate change, according to a new study led by researchers at the NASA Jet Propulsion Laboratory in Pasadena.

Scientists expect seawater to infiltrate underground aquifers in three out of every four coastal areas by 2100, the JPL explained in a news release.

“Called saltwater intrusion, the phenomenon happens below coastlines, where two masses of water naturally hold each other at bay,” the released detailed. “Rainfall on land replenishes, or recharges, fresh water in coastal aquifers (underground rock and soil that hold water), which tends to flow below ground toward the ocean. Meanwhile, seawater, backed by the pressure of the ocean, tends to push inland. Although there’s some mixing in the transition zone where the two meet, the balance of opposing forces typically keeps the water fresh on one side and salty on the other.”

That balance is at risk, however, as higher temperatures melt ice and lead to higher sea levels. Simultaneously, as areas see warmer weather and less rain, groundwater recharge slows, meaning stronger seawater forces are pushing against weaker goundwater.

“All told, due to the combined effects of changes in sea level and groundwater recharge, saltwater intrusion will occur by century’s end in 77% of the coastal watersheds evaluated, according to the study,” the release details.

Images published in the study show that for Southern California, the larger of the two issues is groundwater recharge, meaning local efforts will likely focus on protecting groundwater.

That won’t be the same everywhere, however, as in areas where rising sea levels pose the higher threat, groundwater may need to be diverted.

“Depending on where you are and which one dominates, your management implications might change,” said Kyra Adams, a JPL groundwater scientist and the paper’s lead author.

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