Water Quality in Big Spring Creek
Vol. 10 Issue 1, Spring 2005
By Darrell Schwalm
Spring fed streams are favorite haunts for rainbow trout, even if the stream is on the outskirts of Leesburg, Virginia and in the middle of a residential development. And, where there are trout, there are trout fishermen and women eager to match their wits with the elusive fish. This explains why the Northern Virginia Chapter of Trout Unlimited (NVCTU) adopted Big Spring as a stream restoration project. It also explains why NVCTU asked the Loudoun Wildlife Conservancy to monitor Big Spring on November 10, 2004 to evaluate the health of the stream now that the first phase of the restoration is complete.
Loudoun Wildlife Conservancy members Phil Daley, Darrell Schwalm, and his son Chris helped with the restoration work and did the stream monitoring. Loudoun County Forester, Carol Evans, and Fairfax Riparian Specialist, Dr. Judy Okay, with the Virginia Department of Forestry, provided the trees and technical expertise. John Odenkirk, Virginia Department of Game and Inland Fisheries, provided expertise on fish habitat.
Big Spring is a small watershed located immediately north of Leesburg. It includes a second order stream that drains Morven Park (an equestrian center), a small portion of Leesburg, and a few farms to the west of Route 15. To the east of Route 15, it flows through the low-density residential communities of Big Spring Hamlet and Big Spring Farm subdivisions and into the Potomac River.
In early 2002 the NVCTU signed an agreement with two landowners to restore a section of Big Spring Creek in exchange for authorization to manage catch-and-release fly fishing for Trout Unlimited members. Their aim is to help ensure the continued survivability of the stream’s population of wild rainbow trout. This effort furthers the mission of Trout Unlimited, which is to “conserve, protect and restore North America’s trout and salmon fisheries and their watersheds.”
The restoration plan focused on stabilizing vertical and threatened stream banks to help control erosion and reduce sedimentation. A variety of innovative bioengineering techniques were used to restore the stream in as natural a manner as possible. Natural materials, such as vegetation, root wads, oak stakes, bio-logs, cedar revetments and hay bale gabions, were used. Work on the project was completed in November 2004, after ten workdays involving 223 chapter volunteers who contributed 1,115 hours. Currently under consideration is whether to extend the restoration project downstream over the next half-mile section.
Water quality (WQ) standards depend upon the designated uses of a stream. All streams in Loudoun County are designated for recreational uses, including swimming and boating, and for the support of aquatic life. Whether a stream meets WQ standards depends upon the level of human impact on the land in the watershed.
Land along Big Spring is primarily used for pasturing cows and horses and for low-density housing. As a result, there is little forest cover in the watershed. Also, a major highway intersection crosses the stream. Pollution from these land uses is primarily from non-point sources. This includes runoff from pastures used for cattle and from impervious surfaces on highways and in residential areas. The impact of storm water runoff is aggravated because of very narrow or nonexistent riparian buffers along the stream in many places.
A riparian buffer is the 100 – 200-foot zone on each side of a stream that is vital to good stream health. The picture below shows that the riparian buffer along Big Spring is very poor due to the lack of trees and other woody vegetation along the stream bank. The poor canopy cover deprives the stream of shade to cool the water, leaf litter that is an energy source for the food chain, and woody debris that provides habitat for a diverse community of aquatic insects and fish. The stream bank also lacks roots from trees and woody shrubs that hold the soils from eroding and lacks leaf litter that filters runoff.
Loudoun Wildlife Conservancy’s stream habitat assessment, using the EPA Rapid Bio-Assessment Protocol (RBP II), evaluated the physical habitat in the stream corridor that influenced the quality of Big Spring and the aquatic insect community. The habitat rating for the stream at the NVCTU restoration site was 127 out of a possible 200 points, or 63%. This score was at the bottom of the “marginal” range (60-74%) established by EPA. Low ratings were given for bank vegetation protection, riparian zone, substrate embedment, epi-faunal substrate and available cover, and bank stability.
The assessment showed that bank erosion in Big Spring had resulted in fine sediments filling over 50% of the living spaces for insects around and between gravel and cobble giving the substrate a partial “cemented in” look. The mowed grass allowed storm waters to flow into the stream without the retention and natural filtration provided by leaf litter and porous soils that exist in naturally vegetated buffers.
Benthic macroinvertebrates are the aquatic insects, crayfish and other crustaceans, clams and mussels, snails, and aquatic worms that live in the sediment or on the bottom substrates of streams. They include mayflies, stoneflies, caddisflies, dragonflies, beetles, and midges. These insects and other organisms are excellent indicators to assess streams because they cannot escape changes in water quality. Each organism has requirements for it to flourish which the stream must provide. By determining the number and type of organisms that live in a stream, the quality of the water and the health of the stream can be assessed.
Benthic Macro-invertebrate Rating
In rating Big Spring, aquatic insects were identified to the family level and the non-insects to the order level. Four primary metrics were used: 1.) number of taxa (i.e., different kinds); 2.) number of mayflies, stoneflies, and caddisflies (EPT); 3.) percent dominant taxon; and 4.) the Modified Hilsenoff Biotic Index, which is based on the sensitivity of each taxon to pollution.
The most prevalent aquatic insects in Big Spring were Netspinner Caddis, Riffle Beetles, Sowbugs, Scuds, and Midge larvae ― all insects moderately tolerant to pollution. The only moderately sensitive aquatic insects found were three Small Minnow Mayflies (Baetidae species) and two Casemaking Caddis. The biological condition score was 9 out of 24. This score was in the “fair” range and indicated a “moderately impaired” stream. A plot of the data is provided on the graph.
Big Spring is a marginally impaired stream that is impacted by farming activities and a degraded riparian buffer. The streamside tree planting by NVCTU to help restore the riparian buffer and stream bank erosion control measures that have been installed are positive steps to protect and restore the health of Big Spring.
Additional actions needed to restore the stream include:
Continue to work with property owners to improve the riparian buffers in order to shade the stream, provide needed leaf litter as a food source, stabilize stream banks, and filter pollutants in storm water.
Work with farmers in the upstream sections to fence out cattle in order to reduce stream bank erosion and sediment in the stream.
Provide educational materials to stream-side property owners on environmentally-friendly ways to maintain and fertilize lawns, reduce storm water runoff into streams, and conserve streamside buffers.
Work with the Homeowner Associations to organize a Friends of Big Springs citizens group that will sponsor an Adopt a Stream Program of the Virginia Department of Conservation and Recreation.