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Investigating Stream Health with the Maryland Biological Stream Survey

Department of Natural Resources scientists look for several different indicators to evaluate the overall health of Maryland streams–here’s how they do it

How can the Maryland Department of Natural Resources tell whether a stream is healthy or degraded? State scientists start by looking for critters.

Every year scientists from the Maryland Department of Natural Resources crisscross the state with notebooks, nets, and other equipment looking for insects and other wildlife as part of the Maryland Biological Stream Survey. The scientists collect and analyze bugs, fish, and other indicator species to develop a score that can show whether a stream is biologically healthy or not.

On a crisp fall day in October, as part of DNR’s Science Week, several scientists from the stream surveying team demonstrated how the process works at a tributary stream of the Patapsco River in Ellicott City.

It starts with the benthic macroinvertebrates. These are aquatic animals such as mayflies, caddisflies, dragonflies, stoneflies, and crayfish. Their presence in a stream is one factor that can indicate healthy stream water quality.

DNR Biologist Jackie Sivalia demonstrates to Secretary Josh Kurtz how a D-Net is used to catch macroinvertebrates, and explains how they help her and other scientists evaluate the overall health of the stream.

“The presence of benthic macroinvertebrates provides us with long-term insight into the health of stream, since they must deal with the conditions day-in-and-day-out; whether the water is flowing with sediment from a strong rain storm or baking in the hot summer sun,” said Kyle Hodgson, a DNR biologist. “These creatures give us a deeper insight into overall water quality conditions than a water quality sample taken at a specific time can provide. I like to think of a benthic macroinvertebrate sample of a stream as a movie and a water quality sample as a snapshot.”

At the Patapsco tributary, scientists used a D-net — so named because its frame is shaped like the letter “D” — to scoop the leaves from the stream bed and sift for insects and other critters. That day, they were able to find a dragonfly larva and a few other insects. Certain types of benthic macroinvertebrates such as mayflies, stoneflies, and caddisflies tend to be intolerant of pollution, and therefore are less likely to be present in streams impacted from pollution sources such as suburban or agricultural runoff.

Dragonfly larva found while surveying macroinvertebrates in the stream.

Researchers use the distribution and abundance of specific macroinvertebrates to create a Benthic Index of Biotic Integrity (BIBI) rating for streams. This rating enables them to compare different streams. The Maryland Biological Stream Survey posts the BIBI scores for streams in an interactive map on the DNR website.

Streams are generally rated “poor” in more developed areas of Maryland that receive pollutants from stormwater runoff and other human activities, while streams rated “good” tend to be in less developed areas.

A large diversity of healthy fish is another indicator that a stream is doing well. To search for fish in the Patapsco stream, DNR Secretary Josh Kurtz and several of the stream biologists donned electrofishers that made them look like the Ghostbusters. The backpack devices send an electrical current into the water, which briefly stuns the fish and enables scientists to weigh and count them before the fish recover and are later released.

The scientists also set up two nets across the stream to cordon off an approximately 75-square meter stream section so the fish data they collect can be compared against other stream sections of the same size.

Scientists collected fish including smallmouth bass, redbreast sunfish, white suckers, northern hogsuckers, American eels, and swallowtail shiners. The data collected is later synthesized into what is known as a Fish Index of Biotic Integrity.

DNR scientists have been evaluating stream health throughout Maryland since 1995. They currently sample about 200 streams per year for macroinvertebrates, fish, and environmental factors such as habitat and water chemistry.

Biologists can sometimes tell whether a stream will contain healthy amounts of fish based on the habitat they observe. For example, fish will typically favor a stream that contains a gravel bottom, large rocks, deep pools, and thick streamside vegetation, over sediment-choked streams with muddy bottoms and cleared stream banks.

One unique aspect of the Patapsco tributary site surveyed in October 2023 is that not far downstream is the Patapsco River site where Bloede Dam was removed in 2018, through a DNR partnership with American Rivers.

The number of eels navigating the eel ladder on the remaining Daniels Dam, just upstream from the Bloede site, has increased exponentially since Bloede Dam’s removal, scientists said. DNR staff counted 361 eels in 2020; 3,000 in 2021; and 36,000 in 2022. By mid-October 2023, DNR staff had counted more than 30,000 eels navigating the ladder. The eels live in the river but migrate to the Sargasso Sea in the Atlantic Ocean to spawn and are an important food source for large fish and birds.

As part of the Maryland Biological Stream Survey, DNR scientists will often travel to sites where environmental restoration, dam removals, or other projects are taking place to evaluate how that work is affecting the health of the stream. A set of 28 healthy streams are sampled to be used as a reference stream to frame other evaluations, while other streams are randomly selected to be surveyed.

“We use all these data points to try to understand the conditions of our streams so DNR and others can do the best job at managing, protecting, and restoring streams in Maryland,” said Scott Stranko, director of DNR’s nontidal assessment division.

More information about and data from the Maryland Biological Stream Survey is available on DNR’s website.

By AJ Metcalf, communications director with the Maryland Department of Natural Resources.