So Much Water but None to Drink!

Figure 1. Warm bowl of chicken noodle soup.
Source: TasteofHome.com

On a frigid, snowy day, nothing tastes (or smells!) quite as good as warm, chicken noodle soup. After the first spoonful, I usually notice the soup tastes delicious but needs a little extra flavor. My solution: salt! We use salt on our foods to enhance and balance the flavors in our meal. But at a certain point, one too many grinds of the saltshaker can make the soup overwhelmingly salty. Something similar is happening to our freshwater sources worldwide.

Figure 2. Road salt on boardwalk in
College Park, MD

Throughout the same cold day, trucks are applying road salt to roads, sidewalks, and parking lots. Road salt is applied to the roads to melt the snow and ice for safety purposes. Yearly, Maryland buys 30,000 dump trucks worth of salt each year, or about 230,000 tons, which costs $11 million! The United States uses almost 2 million dump trucks of salt per year, 45 to 87 times the amount Maryland buys. Where does the road salt go after the roads are clear? The salt dissolves and is transported with the melted snow and ice into groundwater and the nearby streams. After multiple winter snowstorms, the streams accumulate more salt, a process called salinization. A study found rivers in Maryland, New Hampshire, and New York have a quarter to a half the saltiness of seawater during the winter and remain elevated during the summer. Our rivers have the salinity of about 1.5 to 2 cans of Campbell’s Chicken Noodle Soup!

Figure 3. The salt concentration is increasing over recent years in
many freshwater sources globally.
Modified from Kaushal (2016).

The term Freshwater Salinization Syndrome describes the process of increasing salinization over time. Salinization does not only impact snowy cold regions but is a global issue. Other sources of salt include building and road materials, construction, fertilizers, water softeners, and even our sewage. The consistently saltier environment drastically alters the chemistry of the water and creates an inhospitable home to many aquatic organisms. Highly sensitive and native organisms are unable to survive in these salty conditions. Salt-tolerant species, on the other hand, thrive in a range of salinities and can easily repopulate and live in the saltier waters. The increase of salt-tolerant species and decline of native or highly sensitive species alters the food web and the ecosystem of the river. 

The influx of salt not only harms aquatic life, but also causes the release of toxic metals into rivers. The metals are attracted to the soil like the positive and negative side of a magnet and want to be touching (Figure 4a). Like a magnet, the soil and the metal also have charges - the soil has a negative charge, and the metals have a positive charge.  When we add salt (Figure 4b), we are adding positive charges into the stream that are more attracted to the soil. The metal is not strong enough to stay attached to the soil particle and is released into the water. The metal flows with the water downstream to the drinking reservoir or to a well where we get our drinking water. In very high doses, these metals can cause a variety of health effects, ranging from nausea, vomiting, and diarrhea to cancers, learning deficiencies, and skeletal abnormalities. 

Figure 4. (a) Without an influx of salt, the metal and soil are attracted to each other.
(b) When salt is added, the salt is attracted to the soil and the metal is released into the river.

Freshwater Salinization Syndrome is an increasingly pertinent problem in freshwater sources worldwide. It is highly unlikely we will stop using road salt. Even if we did, it is extremely difficult to pinpoint all the other sources of salt in our rivers. Therefore, we must continually monitor and sample these impaired rivers year-round and create regulations with consequences for exceeding the salt levels. Currently, the US Environmental Protection Agency has set general salt limits for our rivers, but each state can ignore when the limit is exceeded. We must continue to monitor and holistically manage sources of salt to our freshwater environments before it is too late. 

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References: 

https://www.baltimoresun.com/bal-te.journal18feb18-column.html

https://mde.state.md.us/programs/Marylander/Documents/2013_Stranko_Road_Salt_(final)_TMF_edits.pdf

Kaushal, S.S., Groffman, P.M., Likens, G.E., Belt, K.T., Stack, W.P., Kelly, V.R., Band, L.E., Fisher, G.T., 2005, Increased salinization of fresh water in northeastern United States: Proceedings of the National Academy of Sciences of the United States of America, v. 102, p. 13517-13520.

Schuler, M.S., Canedo-Argulles, M., Hintz, W.D., Dyack, B., Birk, S., Relyea, R.A., 2018, Regulations are needed to protect freshwater ecosystems from salinization: Philosophical Transactions of the Royal Society B, v. 374.

https://www.baltimoresun.com/news/bs-xpm-2006-02-12-0602110117-story.html