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How humans are making earth saltier than ever – Interesting Engineering

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Salt is essential for life, but too much can be deadly. That's the alarming conclusion of a new study that shows how human activities are increasing the salinity of the planet's air, soil, and water, threatening biodiversity, human health, and the stability of ecosystems.
The study, led by University of Maryland Geology Professor Sujay Kaushal and published in the journal Nature Reviews Earth & Environment, reveals that humans disrupt the natural "salt cycle" that regulates the movement and concentration of salt ions on Earth. These ions, such as calcium, magnesium, potassium, and sulfate, are found in rocks, oceans, and living organisms and play essential roles in various chemical and biological processes.
However, human activities such as mining, agriculture, construction, and road treatment release large amounts of salt ions into the environment faster than natural processes can recycle them. This causes salinization, or salt accumulation, in places where it does not belong, such as freshwater sources, soils, and the atmosphere.
Salinization can have severe consequences for the environment and human health. For example, it can reduce the availability and quality of drinking water, damage crops and infrastructure, harm aquatic and terrestrial wildlife, and increase the risk of diseases and infections. It can also trigger "cascading" effects, such as accelerating the melting of snow and ice, creating toxic "chemical cocktails" of salt and contaminants, and altering the climate and weather patterns.
The study estimates that human-caused salinization has affected about 2.5 billion acres of soil worldwide, an area equivalent to the size of the United States. It also shows that salt ions have increased in streams and rivers over the last 50 years, along with the global use and production of salts. Moreover, it reveals that salt has invaded the air as lakes dry up and send saline dust into the atmosphere or as road salts become aerosolized and form sodium and chloride particulate matter.
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One of the significant sources of salt in the environment is road salts, which are used for deicing roads and sidewalks in cold regions. The study reports that the U.S. alone produces 44 billion pounds of road salts yearly, accounting for 44% of its salt consumption and 13.9% of the total dissolved solids in its streams. This can lead to a "substantial" increase of salt in watersheds, affecting the aquatic life and the drinking water supply.
To prevent U.S. waterways from being inundated with salt in the coming years, Kaushal recommended policies that limit road salt or encourage alternatives. Washington, D.C., and several other U.S. cities have started treating frigid roads with beet juice, which has the same effect but contains significantly less salt.
According to Kaushal, it's crucial to consider both short and long-term risks of road salts. While road salts play a vital role in ensuring public safety, they can also negatively impact the quality of water. Kaushal emphasized the need to strike a balance between these competing concerns.
The researchers call this phenomenon the "anthropogenic salt cycle," and argue that it is a global and interconnected problem that requires urgent attention and action. They suggest that reducing the use and emission of salts, improving the management and treatment of saline water and waste, and restoring natural ecosystems and buffers are some of the possible solutions to mitigate the impacts of salinization.
They also propose the creation of a "planetary boundary for safe and sustainable salt use" in much the same way that carbon dioxide levels are associated with a planetary boundary to limit climate change. Kaushal said that while it's theoretically possible to regulate and control salt levels, it comes with unique challenges.
"This is a very complex issue because salt is not considered a primary drinking water contaminant in the U.S., so to regulate it would be a big undertaking," Kaushal said. "But do I think it's a substance that is increasing in the environment to harmful levels? Yes."
Increasing salt production and use is shifting the natural balances of salt ions across Earth systems, causing interrelated effects across biophysical systems collectively known as freshwater salinization syndrome. In this Review, we conceptualize the natural salt cycle and synthesize increasing global trends of salt production and riverine salt concentrations and fluxes. The natural salt cycle is primarily driven by relatively slow geologic and hydrologic processes that bring different salts to the surface of the Earth. Anthropogenic activities have accelerated the processes, timescales and magnitudes of salt fluxes and altered their directionality, creating an anthropogenic salt cycle. Global salt production has increased rapidly over the past century for different salts, with approximately 300 Mt of NaCl produced per year. A salt budget for the USA suggests that salt fluxes in rivers can be within similar orders of magnitude as anthropogenic salt fluxes, and there can be substantial accumulation of salt in watersheds. Excess salt propagates along the anthropogenic salt cycle, causing freshwater salinization syndrome to extend beyond freshwater supplies and affect food and energy production, air quality, human health and infrastructure. There is a need to identify environmental limits and thresholds for salt ions and reduce salinization before planetary boundaries are exceeded, causing serious or irreversible damage across Earth systems

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