“Abrupt salinity increases are expected to occur immediately near the water line.”
Intertidal zones are harsh habitats, exposed to the naked air at low tide and fully submerged at high tide, and yet these areas are inhabited by a wide array of marine creatures. According to a new study published in Scientific Reports, global warming may be making intertidal zone sands even saltier than the seawater that washes over them, putting mussels and crabs at risk, as well as the birds and mammals that feed on them.
Researchers from the New Jersey Institute of Technology's Center for Natural Resources Development sampled seawater near the shore of Slaughter Beach in Delaware, and found that it had a salt concentration of 25 grams per liter. When seawater reaches the intertidal zone, it gets combined with groundwater, which led the researchers to expect that the water below the beach’s surface (aka pore water) would be more diluted than pure seawater.
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But when they measured water from the high tide mark on the beach, the researchers were surprised to find that it was between two and four times saltier than the seawater collected further out.
Models indicated that as temperature rises, the water evaporates out of the beach sediments. Meanwhile, the salt remains trapped between sediments grains. "Evaporation takes out the water and leaves the chemicals in the water behind. Thus, they accumulate,” study co-author Michel Boufadel tells The Science Explorer. “As the water evaporates, the salt amount does not increase in the remaining water, but the salt gets more concentrated as there is less water.”
The researchers write, “an increase in temperature or a decrease in relative humidity (e.g., due to climate change) would not only increase the pore-water salinity in the beach, but would also alter its spatial distribution; abrupt salinity increases are expected to occur immediately near the water line.”
For coastal animals that are adapted to a specific set of conditions in the intertidal zone, global warming, and the intensifying salinity that it is expected to bring about, will disrupt their usual balance, likely leading some to perish and others to move away.
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Editor's note (Aug.16): Paragraph 4 has been edited to include quotes from a researcher involved in the study.
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