Stream Biota Monitoring in Parks of the National Capital Region

By Emma Brentjens and Hannah Harkness, NCRN I&M Science Communications Interns

Logging data during fish monitoring at South Fork Quantico Creek in Prince William Forest Park

NPS

Key Points

• Fish and aquatic macroinvertebrates are indicators of stream health 
• Ecologists observed 48 species of fish and 152 macroinvertebrate taxa in National Capital Region parks during monitoring in 2019-2022*  
• Blacknose dace were the most common fish region-wide, and non-biting midges were the most common macroinvertebrate 
• Fish and macroinvertebrate communities and stream habitat quality varied between and within parks 

*The previous cycle of this periodic (not annual) monitoring occurred 2008-2014.

A Window into Stream Health

The National Capital Region Inventory & Monitoring Network (NCRN I&M) tracks the health of park streams by monitoring fish and benthic (bottom-dwelling) macroinvertebrate communities as well as stream physical habitat characteristics. Macroinvertebrates are small aquatic animals without backbones that are visible to the naked eye. Most of the macroinvertebrates we record in the National Capital Region (NCR) are insect larva that live underwater, like midges, stoneflies, and mayflies. Stream physical habitat characteristics refers to water flow and volume, as well as the solid substrate (stream bed materials) present in the stream.

The NCR includes northern Virginia, the West Virginia panhandle, the District of Columbia, and inland Maryland. This region is rapidly urbanizing. Human activity, climate change, and expansion of buildings and pavement have accelerated storm water flows, heated water temperatures, and added more pollutants into park streams. Stream biota monitoring shows us how park streams are responding to our changing environment.

Fish and macroinvertebrates provide insight into stream health as some species are more sensitive to poor environmental conditions than others. The presence of more sensitive species indicates good stream quality, while an overabundance of organisms that are tolerant of poor conditions may be a sign of habitat degradation.

In addition to being good water quality indicators, benthic macroinvertebrates are a major food source for other aquatic animals. Most fish would not be able to live in the streams without them. Monitoring macroinvertebrate population trends is essential to understanding the entire stream ecosystem.

Scientists partnering with NCRN I&M analyze fish and macroinvertebrate counts as a measure of stream quality using the Fish Index of Biotic Integrity (FIBI) and the Benthic Index of Biotic Integrity (BIBI). These indices score stream health on a scale of 1 (very poor) to 4.99 (good) based on biodiversity, abundance, environmental sensitivity, and other factors. FIBI and BIBI, when analyzed with stream physical habitat characteristics like the diversity of substrates and flow/depth, can provide a comprehensive view of stream health.

Fish and Aquatic Macroinvertebrate Communities

The most abundant species recorded in the region between 2019 and 2022 was blacknose dace (Rhinichthys atratulus), a type of minnow. American eels (Anguilla rostrata) and Blue Ridge sculpin (Cottus caeruleomentum) were also common. Gamefish including brook trout (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss) were recorded at multiple parks.

Blacknose dace were the most abundant fish species in National Capital Region national parks

NPS

American eel found at Catoctin Mountain Park

NPS/Nortrup

Larval midges in the Chironomidae family, which includes the genus Sympotthastia

©David H. Funk. / Stroud Water Research Center

The most commonly identified macroinvertebrate taxon in the region was Sympotthastia, largely due to their high numbers at Blue Blazes Creek in Catoctin Mountain Park. Sympotthastia are non-biting midges, whose larva are better known as bloodworms. Several other common taxa in the region are also different types of non-biting midges. Many non-biting midges are considered tolerant of poor environmental conditions. NCR streams also hosted other types of macroinvertebrates in smaller numbers, including mayflies, stoneflies, and amphipods.

Stream Health Varies Between and Within Parks

Stream biota monitoring did not show a uniform, region-wide trend in stream health. Instead, fish and macroinvertebrate counts and stream habitat data showed variation both between and within parks. During 2019-2022 monitoring, fish community scores in the NCR ranged from 1 at the lowest to 4.7 at the highest, while benthic community scores ranged from 1 to 4.13. This wide range was observed within individual parks. Prince William Forest Park, for example, had some of the highest fish community scores across the region, and at the same time several streams in the park had very poor scores.

Changes in fish and benthic community index scores (FIBI and BIBI) from the previous monitoring cycle (2008-2014) also followed different trends at different streams within the same park. While stream biota metrics at some streams improved, others experienced a decrease in quality. For instance, at Monocacy National Battlefield, BIBI increased at Gambrill Creek but decreased at Bush Creek.

Even within the same stream, FIBI and BIBI did not always follow the same trend. Bush Creek at Monocacy had the highest observed FIBI score (4.7), and a very poor BIBI score (1.38).

The wide range of FIBI and BIBI scores and stream physical habitat conditions in the NCR indicates a need for management strategies targeted toward specific streams. Although stream health varies, high habitat quality in streams across the region shows that parks help protect valuable aquatic habitat and water quality.

Want to know more?

Check out stream fish and macroinvertebrate trends at each park: Antietam, Catoctin, George Washington Memorial Parkway, Harpers Ferry, Manassas, Monocacy, National Capital Parks-East, Prince William, Rock Creek, Wolf Trap

How we Monitor Stream Biota

The National Capital Region Inventory and Monitoring Network (NCRN I&M) monitors stream biota as part of a broader effort to evaluate the health of park ecosystems. Data are collected on fish, benthic (bottom-dwelling) macroinvertebrates, and the physical characteristics of streams. Ecologists then use this data to examine the overall health of stream habitats. This monitoring is crucial for determining trends in species populations, recording the presence or absence of vulnerable aquatic species, and observing changes in the physical habitat of streams. Knowledge of these factors contributes to our understanding of stream and watershed health, which helps to inform management practices in the parks.

After a pilot monitoring phase (2004-2006), long-term stream biota monitoring in NCR parks began in 2008. A total of 37 sites across the region are monitored on a set rotation. Monitoring cycles so far (2008-2014; 2019-2022) are separated by 4 to 5 year intervals based on administrative rather than biological factors. This results in any given site being revisited about once every 10 years. We do not measure variation that may happen in this interval. Monitoring is co-located between fish monitoring, macroinvertebrate assessments, and stream physical habitat analysis.

FIBI and BIBI take into account various criteria, including the number of taxa, abundance of individuals, and the proportion of sensitive, intermediate, and tolerant taxa. FIBI and BIBI scores also consider a stream’s geographic region. For more detail on how geographic region influences scoring, see Standard Operating Procedure #20 of the NCRN Biological Stream Survey Protocol.

Fish species are observed through electrofishing, where a mild electric current stuns fish to the water surface. The monitoring team electrofishes two passes along a 75-meter stream segment. The fish are then netted, identified to the species level, counted, and weighed before release. Game fish are also measured for total length. 

Electrofishing at Taylor Run in Prince William Forest Park

NPS

Macroinvertebrate monitoring at Mary Byrd Branch in Prince William Forest Park

NPS

To evaluate stream macroinvertebrates, monitoring teams mark out a 75-meter stream segment at each site. Organisms are dislodged from approximately 20 square feet of stream habitats and captured in a fine-meshed, D-shaped net. Riffles and other productive spots are sampled preferentially when available. The collected macroinvertebrates are preserved and subsampled to 100 individuals. A list of taxa and their abundance at each site is generated.

Why Taxa and not Species?

Macroinvertebrates can be difficult to identify to the species level due to their small size, lack of species-specific physical characteristics, and the various life stages that are encountered. As a result, most are identified to the genus level when possible, using stereoscopes (low-magnification microscopes). Chironomidae (chironomids or non-biting midges) can be slide-mounted and identified using compound microscopes.

Macroinvertebrate tolerance levels (intolerant/sensitive, intermediate, tolerant) are determined by the Maryland Biological Stream Survey based on an analysis of taxa response to urban and agricultural stressors and reported in the NCRN Biological Stream Survey Protocol.

Further Reading

• Chesapeake & Ohio Canal National Historical Park. 2021. Identifying Insect Communities: Testing DNA Tests. https://www.nps.gov/articles/000/insect-id-testing-dna-tests.htm
• Harkness, Hannah. 2024. Freshwater Jellyfish. https://www.nps.gov/articles/000/freshwater-jellyfish.htm
• Maryland Department of Natural Resources. 2024. Guide To The Maryland Biological Stream Survey Benthic Macroinvertebrate and Fish Indices of Biotic Integrity. https://dnr.maryland.gov/streams/Documents/Guide-MBSS-Benthic-Macroinvertebrate-Fish-IBIs-09-30-2024.pdf
• Myers, Dan. 2024. Freshwater Salinization: Saltier Rivers Are a Growing Concern. https://www.nps.gov/articles/000/salinity.htm
• Nortrup, Megan. 2011. National Capital Region Network Resource Brief: Fish. https://irma.nps.gov/DataStore/Reference/Profile/2188635
• Walker, Nick. 2016. American Eels in the Potomac Watershed. https://www.nps.gov/articles/eels-in-the-potomac.htm