The Hidden World in Your River

Declan McCabe (right), Professor of Biology at St. Michael's College, collects benthic macroinvertebrates with a net while workshop participants identify one on a river stone. Photo credit: Luke Foley

By: Marcy Bucheit, Watershed Engagement Coordinator

Exclamations of delight could be heard as participants huddled around microscopes, peering into the hidden, wriggling world of aquatic organisms collected from the Mad River above Lareau Swimhole. Just minutes earlier, they had waded into the water, disturbing cobbles with their feet upstream from a net that captured these tiny creatures as they drifted downstream.

Now, gathered around petri dishes, the group marveled at their finds while Declan McCabe, Professor of Biology at Saint Michael’s College, guided them through how to identify the many species of “river bugs” they had netted. The workshop, hosted by Friends of the Mad River (FMR), was organized for local educators and Mad River Watch volunteers to learn more about the vital organisms that form the base of the river food chain: benthic macroinvertebrates.

River Bugs
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Benthic macroinvertebrates—the scientific term for small aquatic organisms—includes the larval stage of many flying insects like stoneflies, mayflies, and caddisflies. These insects spend their juvenile, or nymph, stage in the river before emerging as winged adults.

“There are so many curious aspects of these little organisms,” said Marcy Bucheit, FMR Watershed Engagement Coordinator. “I was most interested to learn that benthic macroinvertebrates experience their most rapid growth in the fall and winter. As leaves drop into the river in the fall, they ‘steep’ in the water and break down into more palatable food for the benthics. This fuels their growth through the winter, even in the cold temperatures.”
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“It’s fascinating how we share the river with these organisms, but they’re hidden right under our nose,” Bucheit continued. “They’re most commonly found clinging to rocks or buried in sediment. They are often present in riffles and finding one can be as easy as picking up and flipping over a rock. It’s given me a whole new appreciation for what’s under my feet when I’m wading.”

Fish Food

Benthic macroinvertebrates are also a primary food source for fish and birds. They act as a vital linkage between algae and plant material and the upper levels of the food web. Healthy fish populations depend on robust benthic communities, further demonstrating their significance to the ecosystem.

“A lot of people are really familiar with food webs and how different species are connected on land,” commented Luke Foley, FMR Climate & Education Manager. “However, when it comes to underwater species, we have far less familiarity with the different layers of the ecosystem. This presents a great opportunity to center more education on the foundation of healthy aquatic ecology.”

Indicators of River Health

Benthics are also important as biological indicators of the health of a water body and scientists have been using them for decades to track conditions over time. Many species are sensitive to pollution and poor water quality and, unlike fish, they can’t migrate away to more tolerable areas. In general, the greater the abundance and diversity of benthic species present, the healthier the river. Certain species, such as mayflies and stoneflies, are also generally more sensitive, so their presence reflects healthy water.

“I was amazed at the sheer diversity of insect species we found,” said Julie Frost, FMR Watershed Projects Coordinator. “The indicators we saw that morning, especially the presence of stonefly nymphs and the wide variety of species, reflected a clean and healthy watershed, which is exactly what we’re working to protect.”

Notes from the Field

On August 3rd and 4th, Mad River Watch volunteers visited field sites to collect data and observe environmental conditions, continuing decades of local monitoring on the Mad River and its tributaries.

These sampling dates reflected the continued stretch of dry weather, with many reports of low water levels and more exposed sediment and cobbles. Water temperatures ranged from a low of 59°F at 10:20 a.m. Sunday at Rice Brook to a high of 76°F at 4:45 p.m. at Hooper Lane. Conductivity readings varied, with the highest level recorded at Clay Brook and the lowest at Warren Falls.
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