By Emily Davis
Below the surface of the water, there’s a whole other world wriggling and crawling in the sand, mud, and gravels of the riverbottom. Fly-fishermen have known for years that learning the secrets of stream creepy-crawlies gives a great return on investment when it comes to catching fish. As it turns out, studying these water-dwellers is useful for more than just tying great flies. It’s also an effective strategy for tracking the progress of watershed restoration.
These stream “bugs”—known as aquatic macroinvertebrates to those who study them—can tell us a lot about the health of our streams, rivers, and lakes. ‘Macroinvertebrate’ refers to an animal that’s big enough to see without a microscope (‘macro’) and lacks a backbone (‘invertebrate’), and can include many categories of what are colloquially called “bugs”. The term ‘aquatic macroinvertebrate’ actually includes a variety of aquatic animals like snails, clams, and worms, in addition to insects like mayflies, caddisflies, and midges.
Because macroinvertebrates are sensitive to stream conditions like water temperature, pollutants, and sediment, we can use them as a barometer for water quality. Keeping tabs on abundance and diversity of macroinvertebrates is important for helping the Middle Fork’s juvenile salmon and steelhead thrive, because they are the main food source for these fish—along with other animals like lamprey, mink, otters, and so on. Tracking which groups of macroinvertebrates are present also help us track changes in stream habitat after restoration projects are completed. For example, if a project planted lots of streamside trees and shrubs to help shade the stream, over time we might see more cold-loving macroinvertebrates moving in to the neighborhood.
Justin Rowell, Public Lands Project Coordinator for the North Fork John Day Watershed Council (NFJDWC) explains further: “The various bugs each have a survivability threshold which means if we begin to not find certain bugs, or other bugs start moving in, then we know that stream conditions are changing. Or we can ID reaches that are in need of restoration compared to others.”
Rowell and his colleagues at the NFJDWC, based in Long Creek, OR, are well-acquainted with the secret riverbottom world of aquatic macroinvertebrates and why it matters for stream restoration. As part of their work for the Middle Fork John Day Intensively Monitored Watershed (MFJD IMW), Watershed Council staff travel around the Middle Fork John Day watershed collecting macroinvertebrate samples.
NFJDWC staff use two methods to collect aquatic macroinvertebrates: drift nets and benthic samples. A drift net is a net staked in the middle of the water column to catch whatever is floating downstream on the current—the random bits and pieces of debris that scientists call ‘the drift’, which includes both bottom-dwelling macroinvertebrates, and land-dwelling (terrestrial) ones that have fallen into the stream.
View of two drift nets from the downstream end.
The nets, secured with rebar, are deployed in the morning and collected at the end of the day
Side view of water flowing through a drift net
The waders and stream boots belong to Shelley Reich, Monitoring Coordinator at the Watershed Council. Here, Shelley collects a benthic macroinvertebrate sample near the Oxbow Conservation Area. Using a standard technique, she uses her hands and feet to loosen debris from river rocks. The dislodged debris, which includes many macroinvertebrates, floats into a ‘kick net’.
What does the Watershed Council collect? “Bugs we collect vary,” says Rowell, but “we expect to see a lot of caddisflies—which locals usually call periwinkles—stoneflies, dragonflies, various worms, crayfish, and others. We also find what we call 'water pennies' which are pretty neat little creatures.”
After samples are taken, they are sent to a lab where professionals identify the contents. Once samples have been processed, other scientists, from university researchers to Oregon Department of Fish and Wildlife biologists, can use the data to help answer questions about watershed health, stream restoration and fish populations.
What does the data from the Watershed Council’s aquatic macroinvertebrate monitoring tell us about how stream restoration is changing the Middle Fork watershed? Stay tuned for results!