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Hot and Salty: Good for Snacks, Not for Streams

05/08/2019

We just finished a great season of Winter Salt Watch. But winter is turning to summer very fast. Here in Maryland, some days are already starting to feel like summer with temperatures in the 70s and 80s. And while we may be done monitoring chloride levels for the season, aquatic life is just beginning to feel the impact of that chloride.

When salt gets into waterways, it flows downstream, just like everything else. But the movement of the water can carry the salt to other places too. For example, as water sinks into the soil, it will bring some of the salt with it into the groundwater.

The baseflow of a stream, or the level of water that remains in a stream year-round regardless of rainfall or snowmelt, comes from groundwater. During the hot, dry summer months, when not much surface water is coming into our streams, groundwater continues to feed the flow. As the water comes out of the ground, so does the salt that was stored along with it earlier in the year.

The increasing amount of salt in the stream, combined with low water levels, means that we can see higher concentrations of stream salt in the summer than in the winter. In other words, chloride levels in our local streams can rise even during times when we aren't putting any salt into the environment.

And scientists are learning that chloride can be more harmful to aquatic life during warmer weather. Researchers at the Stroud Water Research Center recently did experiments on Mayfly larvae to see how they were affected by salt under different water temperature conditions. They found that salt was most toxic to Mayflies at higher water temperatures. While stream salt levels may be higher in the winter months, the researchers concluded, the biggest impact of that salt on sensitive aquatic life may occur when water temperatures rise in the spring and summer.

Year-round stream monitoring by citizen scientists can help us understand more about how salt affects aquatic life. If a stream monitor does a chloride test in the winter and finds high salt levels, and then searches for macroinvertebrates in the summer and doesn't find mayflies, that provides evidence that stream health is suffering because of the salt – evidence the monitor can show to local decision-makers when asking them to take action on local water quality by reducing use of road salts.

You can be the stream monitor in this story! Learn how you can get involved in macroinvertebrate monitoring – and join the Clean Water Challenge so you won't miss important updates about next year's Winter Salt Watch. Or read more about where we've learned salt is a problem.