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Body and Soul

(page 7 of 8)


A peek beneath the water

From our lofty human perspective, streams are simple things. They carry water from one place to the next. They offer us places to quench our thirst, shores to sit a spell and ponder, holes for trout to hang out. 

But we never see streams for what they really are: soggy, wedded partners with the world that hovers above them. “That’s the essence of science, to find those connections between the seemingly unconnected,” explained Bruce Medhurst, a staff researcher at the nation’s most-acclaimed mountain stream study facility, the Sierra Nevada Aquatic Research Laboratory.

As Medhurst explained, as it is above the water, so it is below. Just as the sun feeds the grain that we boil into malt for beer, the sun also feeds a stream’s food web.

Algae feeds on sunlight while it clings to submerged rocks like seaweed. The algae also filters “nutrients” out of the water, stuff like fallen leaves and nitrates (primarily by-products of our homes, cars, power tools, etc.). The algae then become a wet buffet line for aquatic insect life. Mayflies, damselflies, stoneflies and their fellow invertebrates work their way from eggs to swimming midges and nymphs to flying terrestrial adults primarily by feasting on algae.

At some point during the process­—either while the bugs are bouncing off the bottom, dancing upon the surface or drifting in between­—the trout sip them up like children slurping milkshakes on a summer’s day. The trout, of course, then occasionally make meals for those outside the stream’s food web—critters higher up on the food chain, like bald eagles, osprey, blue herons and fishermen.

For a long time, though, that’s where the stream’s food web was believed to end. The water was one ecosystem, and the world it cast reflections of was another. But eventually, some curious scientists were able to finally start seeing the secret life of streams.
 “The picture is a lot bigger than we think. Everything is connected,” said Medhurst.

“It’s called a ‘trophic cascade.’ When you cut off something or add something new like an herbicide or fish species to a stream, it’s going to affect everything else. And as humans, it seems like we’re always adding something to streams,” explained Medhurst, who did his undergrad work at Wisconsin-Stevens Point, which isn’t all that far from famous conservationist Aldo Leopold’s beloved Sand County.And as Medhurst pointed out, the more we learn about streams, the more sound Aldo Leopold’s advice seems: “When we see land as a community to which we belong, we may begin to use it with love and respect.”

-Mike McKenna


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