Author: Laura Oleniacz
A preliminary assessment of insect communities in waterways of western North Carolina after Hurricane Helene demonstrated that in most waterbodies sampled, the variety of species as well as the number of each insect species was comparable to before the hurricane. It also identified waterways that had declines in the variety of insect species and abundances.
The results were released recently in a preliminary report that is available online: Hurricane Helene Effects on Benthic Macroinvertebrates of 11 North Carolina Streams, a Preliminary Analysis.
“The structure of the invertebrate community and the background water chemistry in the streams looked pretty good in some places, although we saw a couple of places where the invertebrate community took an extra hard hit,” said Eric Fleek, supervisor of the NCDEQ Division of Water Resources’ Biological Assessment Branch. “Overall, we thought they were in better shape than we were anticipating.”
After Hurricane Helene, biologists with the NCDEQ Division of Water Resources’ Biological Assessment Branch sampled on Nov. 19-22 and Dec. 3-5 at 11 sites across western North Carolina for benthic macroinvertebrates.
Benthic macroinvertebrates, or “benthos,” are small organisms that live on the bottom of streams, rivers and swamps such as mollusks, dragonfly and stonefly larvae, snails and even worms. DWR’s team of biologists travel around the state to sample for these organisms because their presence and abundance are indicators of the health and cleanliness of the water they live in.
After Helene, they conducted sampling at 11 sites in western North Carolina, and they surveyed another 16. Since they wanted to maximize the number of sites they could visit, they limited sampling to select types of invertebrates that fall into the orders, or scientific groupings, of: Ephemeroptera (mayflies), Plecoptera (stoneflies), and Trichoptera (caddisflies), known as “EPT.”
“If we’re doing a full-scale sample, we cover all the invertebrates: mollusks, worms, beetles, dragonflies and damselflies, etc.,” Fleek said. “The full-scale sample also requires more physical samples per habitat type, but we found in some cases, we faced limitations due to impacts to habitat.”
They did not assign full bioclassifications, or ratings, for the waterways since the hurricane was a naturally occurring event, they were sampling outside of their typical timeframe, and other factors.
“We wanted to cover as much area we could,” Fleek said. “We also did not want to displace emergency personnel who also needed lodging, or get in the way of emergency repairs to roads and other infrastructure, so we wanted to get in and out quickly.”
Of the 11 sites they sampled, they found four sites had a similar number of mayflies, stoneflies and caddisflies – the common names for EPT taxa - and were comparable to samples collected before Hurricane Helene.
Seven sites showed a slight decrease in the number, or richness, of each taxon of insect, and four had significantly reduced richness. The four streams that showed significantly reduced richness were Buck Creek and the Catawba River near the public access to the Catawba Falls hiking trail in Old Fort, as well as sites on the Broad River and Hungry River.
Their hypothesis for why some sites had lower richness and abundance of insects than other sites was due to levels of disturbance to habitat, including from concentration of landslides in the area, and damage due to scouring of the waterway and habitat.
“The biggest impacts we found were to the actual structure of the habitats – the velocity of water and material scouring it out,” Fleek said.
They plan to return to these areas in the spring and summer to sample again.
“In some cases, the benthos, at least in terms of the ecology of the insects, seemed to weather this event fairly well,” Fleek said. “We anticipate when we go back again, they will have undergone additional recovery.”
More information about the Biological Assessment Branch is available online: Biological Assessment Branch website. Their classifications for waterways across the state can be found online: Benthic Monitoring Data Map.