Volunteers diagnose health of Muskegon River watershed
EVART — The Muskegon River and Twin Creek in Evart received a clean bill of health after its fall checkup last week.
On Thursday, Muskegon River Watershed Assembly Secretary Doug Trembath and Jean Mortensen, a biology teacher, met in Riverside Park in Evart to conduct a survey of macroinvertebrates in the river and the 300 feet of Twin Creek leading into the river. During the first two weeks of May and September, MRWA sends volunteer river testers like Mortensen and Trembath to 38 sampling sites throughout the watershed, which spans 12 counties, including Osceola, Mecosta and Lake counties.
Testers collect samples from the riverbed's silt, sand, leaf pack and gravel, where they can find macroinvertebrates (otherwise known as bugs), their larvae and possibly their egg casings. These bugs might also attach themselves to large rocks to shield themselves from the current, or to the mud on the riverbanks.
They look for three categories of indicator species: species that are highly intolerant of pollution, such as stone fly nymphs, caddisfly larvae and gilled snails; those that tolerate some pollution, like beetle larvae and crayfish; and others that are very tolerant of contaminants, such as leeches, pouch snails and midge larvae. To qualify a species as being common in the river, researchers must collect at least 11 individual specimens.
Testers also measure the depth of the river in the spots from which these samples are taken, as heavy rains or periods of drought can affect river insect populations. As the seasons change, researchers also might find differences in the concentrations of insects in different areas.
But if a sample includes a some of those creatures that tolerate pollution very well, it doesn't necessarily mean the river isn't healthy.
"You expect to see a little bit of everything" Trembath said. "There's a mathematical formula that weighs the less tolerant higher than the more tolerant. You want to have some diversity."
That is to say, leeches and caddisflies can both inhabit a healthy river or stream, but samples taken from an unhealthy river wouldn't show signs of a caddisfly presence since those insects can't tolerate any pollution.
The Muskegon River and Twin Creek tend to show a great balance of the kinds of bugs researchers expect to find.
"Thank goodness it's always good," Mortensen said.
Conducting these bi-annual river health checks has given Trembath and Mortensen a greater appreciation for the Muskegon River.
Trembath, whose house sits on the river north of Sears, thinks about the river when he takes out his kayak or canoes. For Mortensen, she's reminded of her research contributions whenever she's visited by the full-grown insects she saw as larva.
"Eventually these bugs we look at emerge and become something you swat at in the air," she said. "You do that and then you think, 'Oh, I remember you when you were just a little guy!'"
MRWA always needs new river testing volunteers. Find out more at mrwa.org.