There’s a hidden underground battle going on between fresh water and seawater in the U.S., and for the first time scientists have pinpointed where each side is “winning.”
A new study in the journal Science found that one-fifth of the coastal United States is at risk of contamination between fresh and salt water.
Though huge quantities of the two types of water mix all the time as streams and rivers flow into the ocean, it’s the below-ground mixing that can be especially troublesome.
“It’s a two-way street of vulnerability,” said Ohio State University hydrogeologist Audrey Sawyer, lead author of the study.
Underground freshwater can carry harmful pollution as it makes its way into the ocean, creating coastal dead zones and toxic algal blooms. “This freshwater is right underfoot, flowing around leaky gas and septic tanks,” Sawyer said in an article that accompanied the study in Science.
Seawater can also “contaminate” our underground freshwater aquifers: “It takes only a small amount of sea water to render drinking water non-drinkable, so saltwater invasion is a big concern,” she added.
Though this transfer has been going on long before humans arrived on the scene, it is only recently that we’ve been polluting the water and also become increasingly reliant on groundwater for drinking and irrigation.
The study “removed the cloak from hidden groundwater transfers between land and sea,” said hydrologist Cedric David of NASA’s Jet Propulsion Laboratory, which was also involved in the research.
The study found that 9% of the U.S. coastline — including southeastern Florida,Southern California and Long Island, New York — have water supplies that are susceptible to seawater contamination. This is especially concerning in places like California, which has begun to use more groundwater with surface supplies running low during the state’s devastating drought.
On the other side, 12% of the coast, including the northern Gulf Coast, northern Atlantic Coast and Pacific Northwest, is where the ocean is most at risk of freshwater contamination from septic tanks and fertilizer runoff.
The study includes the first-ever map of the underground flows — technically known as “submarine groundwater discharge” — that connect fresh groundwater under the U.S. and seawater in the surrounding oceans.
“We hope others will use our analysis to better plan strategies for coastal land development and groundwater management that help preserve water quality,” Sawyer said.
“Right now, we’ve created a map of American coastlines that highlights some previously known as well as unknown areas of vulnerability along the U.S. coastline, but we hope to be able to do it for the world shortly, as data become available,” she added.
Source: USA Today
