Fox Creek Park Ecoological Assessment - Stream Biology
V. Stream Biological Assessment
Biological monitoring of streams using benthic macroinvertebrates is a well-established technique that assesses the condition of water bodies using aquatic insects as bioindicators, or “canaries in the coalmine.” (Voshell, 2002). Three representative sample points having substrates where insects and their predators may thrive were sampled
Summary
⮚ A biological monitoring survey of three sites along Fox Creek collected 91 individual aquatic invertebrates (“macroinvertebrates”), and two fish and one crayfish.
⮚ Over 50% of individual macroinvertebrates were collected at Site #3 at the northern end of Fox Creek.
⮚ Using a biological index designed by the Izaak Walton League that weights pollution-sensitive invertebrates over tolerant ones, Fox Creek scored an “Excellent” water quality rating.
⮚ Four species of stoneflies were collected, including Acroneuria, Isoperla, Leuctra and Paragnetina.These stoneflies are very sensitive to pollution and are only found in streams with good to excellent water quality.
⮚ Four species of mayflies were also collected, including Baetis, Ephemerella and Maccaffertium. The latter two are not as oxygen and temperature sensitive as some mayflies, and the former two are considered very intolerant of pollution.
Biological Assessment includes review of the type and numbers of stream “macro-invertebrates” primarily aquatic insects and crayfish, fish, salamanders, and other life forms (i.e., “biota”) at suitable sample points.
Using a kick-net and following protocols utilized by the Izaak Walton League (Izaak Walton League) and multiple government agencies, we sampled Fox Creek on 5/15/2023. Fox Creek is a first-order stream that feeds the Swannanoa River in Buncombe County, N.C.
Streambed substrate consisted mostly of sand or silt (60%), small- to medium-sized gravel (about 25%) and small cobblestones (roughly 15%.) Water temperatures ranged from 15.2 degrees C. to 16 degrees C. The water was clear, with visibility of more than a foot in depth.
Channel Structure of Fox Creek is deeply incised in places, while other areas show signs of bank widening and erosion. It appears that “flashiness” from storm events have caused much of this damage. All three sampling sites we used were adjacent to paved roads and mown grassy areas, which shed water quickly versus riparian forest.
Some aquatic insects such as mayflies and stoneflies are very sensitive to pollution, so their presence in a stream is a strong indication of either good or excellent water quality, whereas their absence is often a sign of organic or thermal pollution problems. (Voshell, Jr.) . Other macroinvertebrates such as midges and aquatic worms can thrive in even degraded streams, so their dominance in a stream often means poor water quality.
In total, 91 macroinvertebrates were collected from three sampling locations along Fox Creek and its unnamed small tributary. Of those, five types of macroinvertebrates (mayflies, stoneflies, caddisflies, riffle beetles and gilled snails) are considered sensitive bioindicators of stream health by the Izaak Walton League and most water quality agencies. (Izaak Walton League).
Five types we found are considered somewhat, or less, sensitive to pollution: crayfish, craneflies, damselflies, aquatic sowbugs (a freshwater isopod) and net-spinning caddisflies in the genus Hydropsyche. Tellingly, only one type of macroinvertebrate sampled is considered to be pollution-tolerant and only three of these -- all midge larva -- were found during our survey.
Using the Izaak Walton League’s formula for calculating biotic values, which weights sensitive species over pollution-tolerant ones, Fox Creek scored a total index value of 26. The IWL considers any index value over 22 to be an indicator of “Excellent” water quality. (Izaak Walton League #)
Probably the biggest surprise of the survey was the diversity of Plecoptera, or stoneflies, found in Fox Creek. As their name suggests, these creatures are usually found in rocky streams, although some species live in leaf packs or other woody vegetation. As a whole, stoneflies demand clean, well-oxygenated water and their presence strongly suggests unpolluted conditions.
In addition to the macroinvertebrate fauna, two vertebrates were found in the course of seining. A Western Blacknose Dace (Rhinichthys obtusus) in vibrant spawning colors was picked up in a kick net at Fox Site 2. Another minnow too small to identify was also picked up there as was a crayfish species. Western Blacknose Dace prefer small headwater streams with moderate to rapid water. They are considered tolerant of pollution, according to the U.S. EPA.
Realistically, while Fox Creek water quality based on aquatic invertebrates ranks as “excellent”, natural and healthier conditions would likely reveal numerous additional species and individuals per species. The creek does not rival aquatic invertebrate resources on pristine streams as seen in nearby National Forest lands in terms of numbers of species, populations and intact fish and aquatic life. However, these findings do indicate that species intolerant of chemical, nutrient, and sediment pollution are thriving on site, and they may be expected to propagate and improve over time as the stream channel is restored and natural, shaded conditions return to streams - and park residents and volunteers have made great progress already in this venture.
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