Restoring streams

Is it possible to bring back a healthy ecosystem?

The quiet stream that meanders in your neighborhood might be great for cooling off on hot days and getting your daily dose of nature, but how can you tell if that stream is healthy and thriving? It’s not as simple as taking its temperature and pressure, but there are some signs and symptoms to look for.

If you’re curious about the health of your stream, look to the small insects skimming the water’s surface. A large diversity of insects such as caddisflies, stoneflies and mayflies signal a working ecosystem. Take a look in the water and notice if there are fish and what kind. Another great sign for stream health in Maryland is migratory fish, such as shad or herring.

Unfortunately, signs of healthy streams are not as prevalent as they used to be. Many streams throughout the Chesapeake Bay watershed have been degraded from growing cities, damaged sewage lines, or point-source pollutants, such as sewage treatment plants and factories. 

Bob Hilderbrand, an associate professor at the University of Maryland Center for Environmental Science’s Appalachian Laboratory, has been examining streams that have been restored to assess whether or not these projects, which can cost up to $1 million a mile, can bring these streams back to the thriving ecosystem they once were.

“A lot of the work I do is examining these stream restorations to see whether or not the ecology, specifically the organisms living in those streams, can be returned to some semblance of a former state,” said Hilderbrand. “We’ll never get back to pristine state, but to even improve a little will be good.”

Degraded streams experience erosion of river banks and cloudiness. A waterway surrounded by impervious surfaces can experience larger flows of water that erode banks and move large amounts of sediment down the system.  In an effort to compensate for the damage caused to these streams, restoration efforts fall into one of two categories: restoring the affected segment of the stream or improving another stream within the watershed.

Can a stream truly be restored?

In assessing the condition of 40 Maryland urban streams that had been restored—or rehabilitated—in the greater Washington, D.C. and Baltimore area, Hilderbrand found both encouraging and discouraging results.

 “There’s good news and there is bad news. As far as the physical structure of the streams and the stability goes, these restorations that we’ve looked at have been very effective,” says Hilderbrand. “Unfortunately, with respect to the biological aspect, the organisms themselves, we are not seeing improvements, it’s disappointing.”

He compared streams that were restored using two different methods: natural channel design or regenerative storm water conveyance.

Natural channel design remediation works to restore the stream to resemble what that stream would look like under undisturbed conditions. This method was used for almost all streams in the Piedmont region of the study area in central Maryland.

Regenerative storm water conveyance is a technique that works best on seasonal streams with slow moving water. By building smaller pools along the stream channel, it allows for improved storm water retention. These smaller pools allow for water to percolate though a couple meters of organic matter, where microbes can extract excess nutrients from the system and prevent it from entering the bay.

Find out more about regenerative storm water conveyance vs. natural channel design

Another way to identify stream health is the stream’s bank stability, such as the levels of stream bank erosion, channel widening, and movement of fine sediments. Restorations Hilderbrand has examined have been extremely successful in terms of stream stability. A decrease in fine sediments seen in waters downstream of the restoration is good news for the fish and invertebrates whose habitats can be clogged by the moving debris.

The Chesapeake Bay also benefits from the decrease in fine sediments, which are often associated with high levels of phosphorus, that travel long distances. Nutrients like phosphorus that end up in the Bay are partially responsible for the dead zones that result in harsh ecological effects. By limiting the movement of fine sediments, restorations are helping lessen the impact of degraded streams on Chesapeake Bay dead zones. These are areas left with little to no oxygen when algae blooms fueled by excess nutrients decompose.

Unfortunately for the insects in this stream, the current outlook on effective stream restoration isn’t as positive.

“Within restored sections they lost their biological quality at rapid rate,” said Hilderbrand.

To assess the status of aquatic insects in these rehabilitated streams, Hilderbrand was looking for species that are associated with less pollution because of their inability to tolerate poor water quality. By looking for critters like mayflies, stoneflies and caddisflies, the quality of biota in the stream can be assessed.

But why were the biota not improving even though the structural stability of streams was?

As the number of impervious surfaces surrounding a stream increased, the restored sections of streams lost quality in biota at a much faster rate. Impervious surfaces like sidewalks, pavement and rooftops allow for water to runoff and wash chemicals and pollutants into streams.

Another factor that might have affected the return of aquatic invertebrates is the invasive nature of stream restoration. The process of restoring degraded streams involves heavy machinery moving through stream channels disrupting the system, which can negatively impact the organic infrastructure. Nutrients stored in sediments that are affected by the machinery store important food for microbes and bugs. With their food supply being potentially disrupted, it decreases the attractiveness of a stream as a home for these organisms.

“If we have these watersheds that are high in impervious surfaces, we can spend a million dollars a mile restoring streams and making some of them look really nice, but as soon as it rains, you’re still going to have the same hydrologic issues,” said Hilderbrand. “Heavy flood flows causes a lot of sediments to come down regardless if the stream channel is stabilized or not. You have sediments coming off the landscape, and it’s just asking too much from the organisms to withstand those sorts of conditions.”

The less degraded a stream is, the easier it is to improve its condition. Restoration is possible but high percentages of urbanized surfaces affect how a stream improves post restoration.

Streams are complex ecosystems and when assessing health, it’s impossible to look at just one factor. Future solutions to degraded streams may be adding insects to the system in hopes of growing a population or exploring other less intrusive methods, but either way these ecosystems are becoming few and far between.