The downstream end of the monitored section of Hoover Creek in Herbert Hoover National Historic Site. National Park Service.
Why watch the animals
Fish and aquatic invertebrates, the insect larvae, worms, crayfish, snails and other animals without backbones that live in streams, say a lot about water quality. They are fairly long-lived and diverse, and they often respond strongly and predictably to changing conditions. Monitoring them reveals the cumulative effects of what happens to a stream, while a standard water quality measurement is only a snapshot.
Species differ in sensitivity. "Tolerant" species survive in a wide range of conditions, while "intolerant" ones decline or move away when conditions change. Tracking which animals live in a stream, along with its habitat, is a sound way to judge its health.
Hoover Creek
Herbert Hoover National Historic Site in eastern Iowa includes 1.3 kilometers of an unnamed tributary of the West Branch of Wapsinonoc Creek, known as Hoover Creek. Its watershed is mostly farmland, rural homes and town. The creek has violated several water quality standards and is listed as impaired under Section 303(d) of the Clean Water Act. Changes in land use can degrade water and habitat and are a major cause of shifts and declines in aquatic life across the Midwest.
The Park Service's Heartland Inventory and Monitoring Network has monitored a downstream section of the creek since 2008 to learn the status and trends of its fish and invertebrates and relate them to water quality and habitat.
Monitoring Hoover Creek. National Park Service.
How the monitoring works
- Invertebrates are collected with a Surber stream-bottom sampler, a special net.
- Fish are caught with a pulsed direct-current backpack electrofishing unit and dip nets. Each is identified, measured, weighed and checked for disease before being released.
- Habitat: the team records the stream's shape, depth and flow.
- Water quality: a calibrated data logger upstream of the invertebrate sampling area records temperature, dissolved oxygen, pH, specific conductance and turbidity, so the results can be compared with the animal community.
What the monitoring found
Invertebrates. Monitoring found 45 kinds of aquatic invertebrates, three of them sensitive to poor water quality. In 2011 the most abundant was a sensitive netspinner caddisfly of the genus Ceratopsyche. Across the four sampling years, though, the community was dominated by animals that tolerate poor water and habitat: true flies of the family Chironomidae, oligochaete worms and mayflies of the family Baetidae. The numbers of all three seem to have declined over time, yet the worms and mayflies made up a larger share of the community in later years. By the Hilsenhoff Biotic Index, the invertebrate community was in fair condition in 2008 and 2014, good in 2011 and fairly poor in 2017.
The Hilsenhoff Biotic Index, a measure of the invertebrate community's condition, for Hoover Creek. National Park Service.
Fish. Ten fish species turned up over the four years, seven of them every year. All were moderately tolerant or tolerant of poor habitat and water quality. Johnny darters, creek chubs and blacknose dace dominated. By the Index of Biotic Integrity, the fish community was in fair condition in most years and just reached good in 2011. The 2017 community looked much like other years, but fish had three times as many deformities, eroded fins, lesions and tumors.
Water. Measurements met state standards, except that turbidity after one rain was 35 times the level measured before it.
Overall, the animal and habitat data put Hoover Creek in fair condition. The findings help managers see how the stream is changing and make informed decisions to protect it.
A closer look: netspinner caddisflies
A netspinner caddisfly larva of the genus Ceratopsyche. National Park Service.
Caddisflies matter in streams: both the larvae in the water and the flying adults are important fish food. Netspinner caddisflies eat algae and other organisms they strain from the water with nets of silk strong enough to hold in fast currents. The nets also create habitat for other animals by slowing the water and even holding large gravel in place. Because caddisflies are sensitive to change and help filter water, break down plant and animal material and build habitat, they are good indicators of a stream's health.
Sources
- National Park Service, Heartland Inventory and Monitoring Network, "Aquatic Community Monitoring at Hoover Creek from 2008 to 2017." https://www.nps.gov/articles/000/aquatic-communities-heho-2008-2017.htm
- Full report: https://irma.nps.gov/DataStore/DownloadFile/702558
Licence: CC0 1.0 (public domain) · Adapted from www.nps.gov
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