Salt Watch: Chloride in the Anacostia Watershed

Picture of Anacostia Riverkeeper

Anacostia Riverkeeper

Even in the DMV’s “snow hole”, winter roadway salt can be a major source of pollution in the Anacostia watershed. Local jurisdictions rely on road salt to make roadways safe when snowy and icy weather conditions are approaching, and the subsequent precipitation washes that road salt into local waterways. When road salt (usually sodium chloride) dissolves into our waterways, it can increase the concentration of chloride in the water. While low levels of chloride can occur naturally due to salts in the soil, levels above 100 ppm can impact watershed health. Our freshwater ecosystems are not equipped to deal with high chloride levels, and increasing chloride levels in streams can harm the fish, macroinvertebrates, and aquatic plants that live in them. 

In winter 2023-2024, Anacostia Riverkeeper joined the Issac Walton League of America’s (IWLA) Salt Watch to monitor levels of chloride in the Anacostia River and its tributaries. IWLA Salt Watch is a nationwide effort to monitor chloride levels across the county, providing strips at no cost to community scientists much like our own! Volunteers adopted a site and monitored monthly, as well as coordinated efforts around major winter storms. Our monitoring gave us a first-hand picture of how the region’s winter salting impacts the watershed’s health. We are thankful for IWLA’s partnership and guidance, as well as our sixteen monitors who braved the winter elements to collect this data with us!

While this winter did not meet expected snow totals, chloride levels did rise after several snow events: both heavy winter storms and no snow busts! Much of the Anacostia’s waterways showed elevated chloride levels through the winter season, particularly after heavy storms in January. We saw two major patterns in our 23-24 winter season:

  • When comparing chloride levels month-to-month, chloride levels spiked in January. January 2024 was marked with two major winter storms, the only major storms to hit during this winter. During January, we saw average chloride levels spike six times higher than they were before winter weather hit in January, showing how road salt might be impacting our watershed.
  • Smaller tributaries showed higher chloride levels than the mainstem of the Anacostia River. Within the river, chloride levels were higher upstream. This data shows that chloride levels may be correlated with water volume, as the larger water volume in the downstream sections of the river (as well as tidal influences!) helps to dilute road salt as it enters the river. Smaller tributaries and upstream sections of the river do not have as much water volume to help with dilution, which may lead to higher salt concentrations after heavy storms.

While salt monitoring is frequently associated with winter storms, continued monitoring through the summer will bring critical data to better understand how chloride moves through the watershed. In addition to road salt, chloride can be introduced to the watershed from overfilled pools or lawn care chemicals. In addition, summertime droughts can reduce water volume in streams, therefore increasing chloride levels. Anacostia Riverkeeper is excited to work with IWLA and our volunteers to continue monthly chloride monitoring through the summer, creating a baseline of chloride levels in our watershed and keeping an eye out for ongoing water pollution. Interested in becoming an Anacostia Riverkeeper Salt Watch monitor? Email us at [email protected] for more info!