Dousman Creek in 2008 (top) and in 2014, after a flood (bottom). NPS.
Effigy Mounds National Monument in Iowa was created in 1949 to protect more than 200 sacred mounds and effigies — earthworks in the shapes of animals and water spirits built by American Indians. Where the Yellow River meets the Mississippi, the park also has forests, goat prairies, rivers and streams.
The NPS Heartland Inventory and Monitoring Network tracks the invertebrates (insect larvae, worms, crayfish, snails and other animals without backbones) and fish of Dousman Creek, a tributary of the Yellow River, to judge the stream's health and catch long-term trends. It is a year-round cold-water stream known as a high-quality native trout stream. Cool- and cold-water species are at risk across the Midwest from rising water temperatures and habitat damage from land use and climate change, so protecting the creek offers them a refuge.
Why watch the animals
Fish and invertebrates live relatively long and are sensitive to water quality and habitat — but not equally. Tolerant species survive a wide range of temperature, murkiness and silt; intolerant ones decline or leave when conditions change. A water sample is a snapshot; the animals living in a stream reveal lasting change.
Collecting aquatic invertebrates with a Surber sampler. NPS.
The network has monitored the creek since 2008, measuring water quality (temperature, dissolved oxygen, pH, conductivity and turbidity), habitat (width, depth, current and streambed material) and the animals — which species, how many, and in what proportions. The same stretch was sampled in July or August of 2008, 2014 and 2017.
Monitoring sites on Dousman Creek: the water-quality site (triangle) and the sampled reach just east of it (thicker shading). NPS.
What they found, 2008–2017
The data suggest the creek is in fair to good condition, though more sampling is needed.
- Fish. In 2008 and 2017, cold-water species that need good habitat and clean water dominated: brown trout (Salmo trutta) and mottled sculpin (Cottus bairdii). In 2014 the community was upended: white sucker (Catostomus commersonii) and johnny darter (Etheostoma nigrum), which tolerate warm and changing water, took over — probably because a large flood outside the park earlier that summer had scoured the bed and laid down fine sediment.
- Invertebrates. In 2017 there were more than ten times fewer individuals than before, and the dominant animals had shifted from two moderately intolerant groups — the mayfly Pseudocloeon and the blackfly Simulium — to the tolerant mayfly Baetis and worms (Oligochaeta).
- Water and habitat. Water quality met Iowa Department of Natural Resources standards every year, but the streambed changed greatly in the 2014 flood. Floods, human activity upstream and the resulting sediment could harm the creek's native fish and invertebrates, and monitoring will continue.
Fish caught in Dousman Creek by species, 2008, 2014 and 2017. White suckers and johnny darters surged in 2014. NPS.
Electrofishing, then and now
NPS scientists have counted fish by electrofishing for more than forty years; a 1973 photo from Sequoia and Kings Canyon National Parks looks much like today's work. In Dousman Creek, one person carries a backpack unit that sends pulsed direct current into the water while others scoop up the stunned fish with dip nets. Each fish is identified, measured and checked for disease or abnormalities, and soon recovers.
Backpack electrofishing in 1973 (left) and now (right). NPS.
Sources
- National Park Service, Heartland Inventory and Monitoring Network, "Aquatic Community Monitoring at Effigy Mounds National Monument." https://www.nps.gov/articles/000/aquatic-communities-efmo.htm
- Full report: https://irma.nps.gov/DataStore/DownloadFile/691934
- Rewritten in hubnx's own words.
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