North American waterways becoming saltier and more alkaline
Across North America, streams and rivers are becoming saltier, thanks to road deicers, fertilizers and other salty compounds that humans indirectly release into waterways. At the same time, freshwater supplies are becoming more alkaline.
Salty, alkaline freshwater can create big problems for drinking water supplies, urban infrastructure and natural ecosystems. For example, when Flint, Michigan, switched its primary water source to the Flint River in 2014, the river’s high salt load combined with chemical treatments to make the water more corrosive, causing lead to leach from water pipes and creating that city’s well-documented water crisis, phys.org wrote.
A new study led by University of Maryland researchers is the first to assess long-term changes in freshwater salinity and ph at the continental scale. Drawn from data recorded at 232 US Geological Survey monitoring sites across the country over the past 50 years, the analysis shows significant increases in both salinization and alkalization. The study results also suggest a close link between the two properties, with different salt compounds combining to do more damage than any one salt on its own.
“We created the name ‘Freshwater Salinization Syndrome’ because we realized it’s a suite of effects on water quality, with many different salt ions linked together. We didn’t know that before,” said Sujay Kaushal, a professor of geology at UMD and lead author of the study.
“Many people assume that when you apply salt to the landscape it just gets washed away and disappears. But salt accumulates in soils and groundwater and takes decades to get flushed out.”
The researchers documented sharp chemical changes in many of the country’s major rivers, including the Mississippi, Hudson, Potomac, Neuse, Canadian and Chattahoochee Rivers. Many of these rivers supply drinking water for nearby cities and towns, including some of the most densely populated urban centers along the Eastern Seaboard.
According to Kaushal, most freshwater salinization research has focused on sodium chloride, better known as table salt, which is also the dominant chemical in road deicers. But in terms of chemistry, salt has a much broader definition, encompassing any combination of positively and negatively charged ions that dissociate in water. Some of the most common positive ions found in salts — including sodium, calcium, magnesium and potassium — can have damaging effects on freshwater at higher concentrations.
“These ‘cocktails’ of salts can be more toxic than just one salt, as some ions can displace and release other ions from soils and rocks, compounding the problem,” said Kaushal, who also has an appointment in UMD’S Earth System Science Interdisciplinary Center.
“Ecotoxicologists are just now beginning to understand this.”
The current study is the first to simultaneously account for multiple salt ions in freshwater across the US and southern Canada. The results suggest that salt ions, damaging in their own right, are driving up the ph of freshwater as well, making it more alkaline. Over the time period covered by the study, the researchers concluded that 37 percent of the drainage area of the contiguous US experienced a significant increase in salinity. Alkalinization, which is influenced by a number of different factors in addition to salinity, increased by 90 percent.
“Our study is the first to document a link between increased salinization and alkalinization at the continental scale. Until now, we didn’t fully appreciate the role that different salts play in altering the ph of streams and rivers of our country,” said study coauthor Gene Likens, president emeritus of the Cary Institute of Ecosystem Studies and a distinguished research professor at the University of Connecticut.