New Scoring Scale Tracks Harmful Effects of Salt Pollution in Streams and Rivers

The Potomac and Anacostia rivers, Rock Creek and other local waterways scored poorly on a new five-stage scale developed by University of Maryland scientists and colleagues to track damage from salt pollution and guide decision making about the amount of salt we add to the environment—primarily to make winter travel safer and easier.

The UMD-led study, published today in the journal Limnology and Oceanography Letters, sheds light on how salinization from winter road salt combined with other pollutants creates “chemical cocktails” that can jeopardize the ecological balance of waterways.

“We realize this is a really diverse problem that’s caused by road salt, but also other sources of salt pollution in our environment—the fertilizers we put on crops, the sewage we put out, the roads that break down,” said the study’s lead author, Sujay Kaushal, a professor in UMD’s Department of Geology and Earth System Science Interdisciplinary Center.

Over time, many streams and rivers around the world have become saltier and more alkaline, previous studies have shown. Salt—which refers to a wide variety of different compounds in water beyond just sodium chloride, or table salt—can affect drinking water supplies as well as aquatic organisms and biodiversity. It can also enhance the mobilization of pollutants including nitrates, phosphates, radionuclides and metals.

Kaushal has been studying this problem—which he and his team named Freshwater Salinization Syndrome—for nearly two decades. In this new study, they found that road salts combined with other human-made pollutants create conditions that periodically exceed certain regional Environmental Protection Agency (EPA) limits for aquatic life, as well as other quality standards in use around the world for drinking water and agriculture.

After analyzing and reviewing both local and global data, the authors identified five major risk factors for Freshwater Salinization Syndrome, which are based on climate, geology, flow paths, human activities and time. They defined stages of the syndrome’s progression and developed a five-tier scoring system “to identify and track unhealthy progression of salinization in our rivers in much the same way we would track an illness or disease like cancer,” Kaushal said. “We have to look at this unhealthy Salinization Syndrome from a systems-level perspective if we’re going to develop guidelines for diagnosing harmful levels and treat the problem.”

The scale ranges from pristine water quality to that indicative of a major breakdown:

Stage 0: Highest water quality, minimally disturbed
Stage I: Abnormally elevated concentrations of one or more salt ions across one season
Stage II: Chronically elevated concentrations of salt ions across multiple seasons
Stage III: Formulation of harmful chemical cocktails exceeding water quality thresholds
Stage IV: Systems-level failures in infrastructure and ecosystem functions and services (drinking water and biodiversity)

D.C.-area waterways have salt levels exceeding water quality thresholds, scoring higher than Stage II at various times during the year, Kaushal’s research team found.

“If you look at the Potomac River, it can exceed the EPA regional aquatic life criteria for salt, and the Anacostia River can exceed the United Nations salt limit for crop growth,” Kaushal said. “Parts of the Potomac, the Anacostia and Rock Creek waterways are in Stage III on the scale for at least part of the time, depending on weather, road salt and other factors.”

Gene E. Likens, a co-author and ecosystem ecologist from the Cary Institute of Ecosystem Studies and the University of Connecticut, said the new study is an important step forward in understanding the impact on road salts on waterway ecology.

“The identification and analysis of critical state factors is a major advance in our understanding and management of Freshwater Salinization Syndrome,” he said.

The publication’s other co-authors hail from the Environmental Protection Agency, the University of Connecticut, Virginia Tech, Chattham University, the University of Virginia and Georgetown University; several co-authors are members of Kaushal’s team at UMD.

The new salinization scorecard could be a useful tool in diagnosing and treating Freshwater Salinization Syndrome in waterways locally and worldwide, the authors said. Armed with this information, policymakers could address regulations to better manage winter salt application as well as other forms of salt pollution that contribute to the problem.