Suburban runoff is one of the biggest challenges to the health and vitality of the TTF watershed. Runoff is rainwater that flows off of roofs and roads, where it ends up in our creeks, leading to flooding and erosion.
When salt is applied to roads in the wintertime, the impact on the health of our watersheds is often not considered. During a snowy winter day, roadway safety is at the forefront of everyone’s mind. After salt is applied to the roads, the snow melts and no one gives it another thought. However, the salt doesn’t just disappear. All of this salt ends up in our creeks in a matter of days when the snow melts, leading to high spikes in the salt level of the stream over a short period of time. Salt can also enter the soil, ending up in the groundwater which naturally feeds our streams; this condition can lead to an elevated salt level throughout the year, not just during the wintertime.
We have been searching for better ways to measure salt levels in our streams throughout the year. We first began to notice these elevated winter salt levels in the Tookany Creek and its tributaries in the winter of 2018, through Izaak Walton League’s Salt Watch.
Salt Watch is a nationwide program in which volunteers test salt levels in streams using test strips. In partnership with Stroud Water Research Center, we installed two water sensors set up in Shoemaker Run which continuously log data about the water quality. Last winter we began to gather data that indicated that this stream could be reaching the saltiness of seawater!
The extreme spikes in salt levels that we saw in Shoemaker Run made us wonder what the levels might look like in other tributary streams in the winter. We also wondered what the salt levels looked like throughout the year, hypothesizing that if there’s this much salt in the stream during the winter, there must be an impact on our streams in the warmer months. This prompted us to work with our volunteers to gain a better understanding of the baseflow or resting state salt levels in our watershed throughout the year.
Working with Stroud Water Research Center, we hosted two chloride blitzes, “synoptic” sampling events, in which multiple volunteers collect a number of water samples across a wide geographic area over a short period of time. These chloride blitzes are a way to measure how much salt is present during non-winter months since salt enters our streams in these months through salt-polluted groundwater.
Elevated salt levels in warmer months can be more harmful to aquatic life than during the winter season. Streams in warmer weather have lower overall water levels, as well as higher water temperatures. When water temperatures are higher, salt can be more toxic, which is why even comparatively lower levels of salt in the summer can negatively affect aquatic life in the creek.
Here’s a graph showing the salt levels observed in TTF headwater creeks during the Fall Chloride Blitz event. The green bar represents a natural stream salt level. All of the streams tested showed signs of salt pollution. One stream even had salt levels above the EPA’s chronic threshold for aquatic life. According to the EPA, a chronic threshold is a 4-day average level that is not exceeded more than once over a period of 3 years.
Figure 2 shows salt readings from sample sites during the October 22 sampling event. The area in red represents readings that are above the chronic threshold for aquatic life from the EPA of 230 mg/L. The area in green is an approximation of a natural stream salt (chloride) level. In addition to these EPA thresholds, the Canadian threshold is 120 mg/L. Additionally, Maryland and Ohio cite levels as low as 50 mg/L affecting aquatic life.
As we continue to sample new sites and sample sites multiple times, we will be able to develop a clearer overall picture of salt levels and how they change over time. Analyzing the data collected through these volunteer events has been critical in creating a better-informed picture of TTF Watershed salt levels. Before these events, we only had data on a few streams in our watershed, with no idea of chloride levels in many of the tributary streams that dot our suburban watershed landscape.
We are now working to develop a more comprehensive picture of the watershed. The data has been used to update our Road Salt Factsheet.
We have presented this data in discussions about road salt use with our municipalities. We use the snapshot data from these events to think more strategically about where to install continuous monitoring equipment, in order to further examine salt pollution in our streams.
Read the full 2022 Chloride Blitz report here, complete with all data and figures.
If you’d like to get involved with our Streamkeepers, our water quality community science volunteers, contact Ryan Neuman at ryan@ttfwatershed.org.
