Salinity and Alkalinity of US Streams and Rivers on the Rise

Innovative research published in the Proceedings of the National Academy of Sciences, reports that streams and rivers in the United States are exposed to a mixture of salts due to human activities. This in turn affects drinking water supplies and infrastructure. The study is the first of its kind to evaluate the combined, long-term alterations in freshwater salinity and alkalization throughout the country.

The researchers used streamwater data of the past 50 years from 232 U.S. Geological Survey monitoring sites, and discovered that a notable increase in salinity was evident in 37% of the drainage area of the contiguous United States, including a 90% concurrent increase in alkalization.

Salt ions, hazardous on their own, have been increasing the pH of freshwater; rendering it increasingly alkaline. Alkalinity and pH govern the quality of water and could impact the stability of water delivery infrastructure, such as pipes. For instance, in 2014, when the primary water source for Flint in Michigan was switched to the Flint River, the high salt load of the river resulted in leaching of lead from water pipes, leading to the city’s well-known water crisis.

Gene E. Likens, co-author of the study and president emeritus of the Cary Institute of Ecosystem Studies and a distinguished Research Professor at the University of Connecticut, Storrs explained that “Long-term monitoring is vital to understanding the pressures facing our nation’s freshwaters from increased salt loading, and for guiding strategies that protect drinking water. Road salt, irrigation runoff, and sewage are obvious culprits. But so is acid rain, which can release alkaline salts that compromise the chemical integrity of freshwaters.”

Evident chemical changes were observed in various major waterways of the country, such as the Chattahoochee, Hudson, Mississippi, Neuse and Potomac Rivers. The majority of these rivers provide drinking water to adjacent towns and cities, including some of the very thickly populated urban centers along the Eastern Seaboard.

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.

Sujay Kaushal, Lead Author

The sources for increased salt levels in waterways differ from region to region. In the Northeastern part of the United States, the major source is sodium chloride, which is used to maintain roads in the winter season. In the Midwest, the major source is fertilizers, specifically those that have higher potassium content. In the remaining regions, weathering of concrete, rocks and soils as well as mining waste liberates magnesium and calcium salts into adjacent waterways.

According to Kaushal, “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 study, which includes inferences for salt regulation and freshwater management approaches, is the first of its kind to record a connection between increased salinization and alkalization at the continental level. Moreover, it is a crucial indication that when various salt compounds become amalgamated, their hazardous impacts are compounded.

“Until now, we didn’t fully appreciate the role that different salts play in altering the pH of streams and rivers of our country,” stated Likens. “Salt content and pH are fundamental aspects of water chemistry, so these are major changes to the properties of freshwater.”

“This research demonstrates the value of long-term data in identifying potential threats to valuable freshwater resources,” stated John Schade, director of a National Science Foundation Long-Term Ecological Research program. “Without such long-term efforts, such widespread and significant degradation of water quality by human activities would remain unknown. Now that we know this is happening, we can begin to unravel the causes and develop strategies to mitigate potential effects on public health.”

As detailed in the Cary Institute report “Road Salt: Moving Toward the Solution,” there already exists specific approaches for dealing with road salt pollution, which include using brine to restrict ice formation on roads, pre-wetting of salt to enable it to get stuck to roads, decreasing sand’s salt content and using weather information systems and pavement sensors to steer salt application.

“Also, not all salts are created equally in terms of their ability to melt ice at certain temperatures,” stated Kaushal. “Choosing the right salt compounds for the right conditions can help melt snow and ice more efficiently with less salt input, which would go a long way toward solving the problem.”

The researchers also stated that urban development approaches such as designing highly effective stormwater drainage systems and principally building further from waterways can decrease the amount of salt taken away from weathered concrete. They also advocate the monitoring and replacement of older drinking water pipes affected by scaling, corrosion or the accumulation of microbial films and mineral deposits.

According to Likens, “In the US, many rely on a patchwork of aging pipes to bring drinking water into their homes. Lead in pipes, solder, and joints is not uncommon, especially in our older cities. These pipes are vulnerable to saltier, more alkaline water, which can release toxic metals, such as lead, and other contaminants.”

“The trends we are seeing in the data all suggest that we need to consider the issue of salt pollution and begin to take it seriously,” stated Kaushal. “The Environmental Protection Agency does not regulate salts as primary contaminants in drinking water at the federal level, and there is inconsistency in managing salt pollution at the local level. These factors are something communities need to address to provide safe water for future generations.”

Michael Pace from University of Virginia, Ryan Utz from Chatham University, Shahan Haq from University of Maryland, Julia Gorman from University of Maryland, and Melissa Grese from University of Maryland are the additional coauthors of the study. The National Science Foundation partially funded the study.