Stream Life at Manassas National Battlefield Park

Young’s Branch at Manassas National Battlefield Park. U.S. National Park Service

Key Points

• Stream biota was monitored at Manassas in 2022 during the 2019–2022* monitoring cycle.
• Fish Community health** **was fair. Twenty-two species of fish were observed in Young's Branch.
• Macroinvertebrate Community was considered poor. Thirty-three aquatic macroinvertebrate taxa were observed.
• Stream Physical Habitat characteristics were mostly marginal or suboptimal.

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

Stream Monitoring at Manassas occurs at Young's Branch.

Scientists working with the National Capital Region Inventory & Monitoring Network (NCRN I&M) monitor the health of fish and macroinvertebrate communities in Young’s Branch at Manassas National Battlefield Park. They assess stream fish and macroinvertebrates using the Fish Index of Biotic Integrity and the Benthic Index of Biotic Integrity. These scoring systems take into account the number of taxa; abundance of individuals; and the proportion of taxa that are sensitive, intermediate, or tolerant to disturbance; as well as comparisons with biological communities expected in environments like Manassas’. Scientists also collect data on the physical characteristics of these streams to assess the habitat they provide.

The park sits within the Piedmont physiographic province, which consists of highly weathered complex metamorphic and igneous rocks. Most of Manassas is used for agriculture, and a small portion of the park is covered in Eastern Deciduous Forest.

Fish Community

Green sunfish was the most abundant species in Manassas in 2022. U.S. National Park Service

Fish Index of Biotic Integrity

Young's Branch received a FIBI score of 3 (fair) in 2022. This score is an improvement from previous monitoring cycles during which FIBI was poor.

FIBI scores use data such as the abundance of fish that are disturbance tolerant, insect-eating, omnivorous, or benthic to assess stream health. Scores range from 1 to 5, with four possible ratings: very poor (1–1.99), poor (2–2.99), fair (3–3.99), and good (4–4.99). Figure 1 shows FIBI scores for Young's Branch.

Figure 1. Fish Index of Biotic Integrity (FIBI) scores for Young's Branch at Manassas. Scores are measured on a scale of 1 to 5 which are categorized as follows: 1–1.99 = very poor, 2–2.99 = poor, 3–3.99 = fair, 4–4.99 = good.

Narrative figure description

Fish Index of Biotic Integrity ranges from 1 to 5. Gray bars indicate 2010 data, while white bars show data from 2022. The background of the bar plots is split into four differently shaded regions based on the score categories described in the figure caption.

Species Found

In 2022, 22 species of fish were observed at Young's Branch, an increase from the 16 species recorded in 2010. Overall fish abundance increased considerably, from 130 individuals in 2010 to 346 in 2022. Green sunfish (Lepomis cyanellus) were the most abundant fish species observed with 76 individuals.

The spottail shiner is a sensitive fish species found in Young's Branch. Robert Aguilar / Smithsonian Environmental Research Center (CC BY 2.0)

Of the species found at Manassas, seven are considered sensitive to environmental degradation: spottail shiner, fallfish, margined madtom, central stoneroller, cutlips minnow, common shiner, spotfin shiner, and northern hogsucker.

The number of game fish recorded at Manassas increased from eight largemouth bass in 2010 to 27 largemouth bass and two smallmouth bass in 2022.

Young’s Branch Fish Species

2022 FIBI: 3 (fair)

*Game fish

Macroinvertebrate Community

Like fish, macroinvertebrates are water quality indicators. Some taxa, such as certain types of dragonflies, worms, and non-biting midges, can tolerate poor environmental conditions. Others, including mayflies, stoneflies, and caddisflies, are more sensitive to higher temperatures and pollution levels.

In addition, macroinvertebrates are a major food source for other aquatic animals. Most fish would not be able to survive without them.

Benthic Index of Biotic Integrity

In 2022, the Benthic Index of Biotic Integrity (BIBI) score at Young's Branch increased slightly to 2.95 (poor), which is nearly considered fair.

Like FIBI, BIBI scores are used to evaluate stream health and take into account the tolerance and abundance of macroinvertebrate taxa, as well as the way each organism feeds and its habitat. BIBI scores range from 1 to 5, with four possible ratings: very poor (1–1.99), poor (2–2.99), fair (3–3.99), and good (4–4.99). Figure 2 shows BIBI scores for Young's Branch.

Figure 1. Benthic Index of Biotic Integrity (BIBI) scores for Young’s Branch at Manassas. Scores are measured on a scale of 1 to 5 which are categorized as follows: 1–1.99 = very poor, 2–2.99 = poor, 3–3.99 = fair, 4–4.99 = good.

Narrative figure description

Benthic Index of Biotic Integrity ranges from 1 to 5. Gray bars indicate 2010 data, while white bars show data from 2022. The background of the bar plots is split into four differently shaded regions based on the score categories described in the figure caption.

Taxa Found

In 2022, 33 benthic (bottom-dwelling) macroinvertebrate taxa were observed at Manassas, similar to the 37 taxa recorded in the previous monitoring cycle. Eukiefferiella (non-biting midges) was the most commonly identified taxon at Young’s Branch, accounting for 14.6% of macroinvertebrates recorded at the stream. The relative abundance of Eukiefferiella has increased since 2010 when it was not recorded in the stream at all. Likewise, the second-most common taxon in 2022, a sensitive genus of stoneflies called Perlesta, was the fifth-most common taxon in 2010, accounting for only 6.1% of observations. The increase in the sensitive genus Perlesta may indicate improving stream conditions.

Young’s Branch Top 5 Most Common Macroinvertebrate Taxa

Table shows five most common taxa of 33 total found

2022 BIBI: 2.95 (poor)

*Sensitive to environmental stress

Stream Physical Habitat Monitoring

Observations of stream physical habitat are gathered at the same location and time as macroinvertebrate monitoring in spring and fish monitoring in late summer. The physical habitat characteristics fall into two broad categories: solid substrates (stream bed materials), and stream flow and depth.

Solid Substrates

• Embeddedness of substrates: higher embeddedness = less available habitat for small fish, macroinvertebrates, and periphyton (small surface-growing organisms)
• Epifaunal substrate: the amount and variety of hard materials that can be used as habitat
• Instream habitat quality: higher values = greater variety of habitat and substrate particle sizes

Stream Flow and Depth

• Pool quality: diversity of slow- and still-water habitats. Higher scores = more optimal habitat
• Riffle quality: depth and complexity of riffles (shallow flows disrupted by substrate)
• Water velocity and depth: higher scores indicate greater variety of water speeds and depths

All characteristics except embeddedness of substrates are measured on a scale of 0–20, with 20 being the most optimal habitat conditions. Embeddedness is measured as a percent.

NCRN I&M no longer reports index scores for stream physical habitat but instead provides data on individual measures. These, along with FIBI and BIBI, provide a comprehensive view of stream quality. Other stream physical habitat characteristics observed but not reported here include the quantity of woody debris and root wads in the stream, stream bank stability, percent of channel shaded, distance from nearest road (remoteness), and land cover composition (percent urban, forested, and agricultural land).

Stream habitat quality scores were marginal or suboptimal at Manassas (Figure 3). Epifaunal substrate remained constant, while the scores for all other habitat characteristics declined from the 2010 value.

While the quality of several stream habitat characteristics declined at Young’s Branch, embeddedness, a measure of habitat availability, improved considerably (Figure 4).

Figure 3. Stream physical habitat characteristics of Young’s Branch in 2010 and 2022. Epifaunal substrate, instream habitat, pool quality, riffle quality, and velocity/depth are all measured on a scale of 0–20, categorized as: 0–5 = poor, 6–10 = marginal, 11–15 = suboptimal, 16–20 = optimal.

Narrative figure description

Bar plot showing stream physical habitat quality scores, ranging from 0–20, on the y-axis for Young's Branch. Stream physical habitat quality characteristics are listed on the x-axis from left to right as follows: epifaunal substrate, instream habitat, pool quality, riffle quality, velocity/depth. Gray bars indicate data collected in 2010 and white bars indicate data collected in 2022. The background of the bar plots is split into four differently shaded regions based on the habitat quality score categories described in the figure caption.

Figure 4. Embeddedness at Young's Branch in 2010 and 2022. Embeddedness is a percent; values above 55% indicate less available habitat and poor habitat quality.

Narrative figure description

A bar plot showing embeddedness as a percent at Young’s Branch in Manassas National Battlefield Park, with 0 percent at the top of the y-axis and 100 percent at the bottom. The bottom region of the graph is shaded red to represent values of 55% or more embedded, which indicate poor stream quality. Values below 55% are considered minimally impaired. Gray bars indicate data collected in 2010 and white bars indicate data collected in 2022.

Conclusions: Slight Improvements in FIBI and BIBI

Both fish and benthic macroinvertebrate scores improved slightly at Young’s Branch, which may indicate higher stream quality. The stream saw an increase in overall fish abundance, game fish, and fish species richness. The increased relative abundance of sensitive stoneflies in the genus Perlesta also points to a healthy stream habitat.

Young’s Branch declined in multiple stream physical habitat metrics. At the same time, the decrease in embeddedness indicates increased habitat availability for fish and macroinvertebrates.

Learn More about the National Park Service's Inventory & Monitoring Efforts

To help protect natural resources ranging from bird populations to forest health to water quality, National Park Service scientists perform ecological Inventory & Monitoring (I&M) work in parks across the country. The National Capital Region Network, Inventory & Monitoring program (NCRN I&M) serves national parks in the greater Washington, DC area. Visit the NCRN stream biota monitoring webpage to learn more. Previous cycles of fish, macroinvertebrate, and stream physical habitat monitoring were reported in 2012 and 2013.

Part of a series of articles titled
Stream Biota Monitoring in the National Capital Region.

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Stream Life at Harpers Ferry National Historical Park

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Stream Life at Monocacy National Battlefield

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