I don’t quite know what to do with myself in this warm fall weather. Shouldn’t we be crunching through snow or at least hiking on frozen ground? Shouldn’t my watercraft all be in storage and my skis be by the front door? Instead, on an afternoon in late October, I found myself on the shore of Lake Namakagon, paddleboard resting at my feet.
Stand-up paddleboarding is a new skill I picked up this summer. I found it useful for navigating swells on Lake Superior, and spent a day exploring the sea caves. Far more often, though, I’d get done with a bike ride, paddle out beyond the weeds and muck at my shoreline, and using the paddleboard as a swim raft, jump in! Even though it was much warmer than the big lake, a dip in Lake Namakagon was refreshing.
But on that October day, the gentle waves that lapped at my toes were bright green. In almost any other circumstance I’d find that color beautiful, but the thick soup of algae made my stomach drop. There would be no refreshing swim.
I stared at my feet for a minute, deciding whether or not I should even attempt to paddle through the goo. Then a spot of deep red caught my eye. Among the dark gray rocks along the shore was one lovely pebble made of jasper. That lifted my mood just enough to propel me away from shore.
As my paddle created swirling patterns in the green scum, I struggled with finding beauty in such a mess. This, I guessed, was a bloom of blue-green algae. Warm weather, calm winds, and plenty of nitrogen and phosphorus from lawns, farms, and autumn leaves increasingly lead to algae blooms in late summer and early fall.
Algae are the base of the aquatic food chain. They use energy from the Sun to transform carbon dioxide and water into sugar. Tiny zooplankton eat the algae, and bigger critters eat the zooplankton, eventually feeding fish, eagles, and us. Blue-green algae aren’t true algae, though. They are a type of bacteria who invented photosynthesis.
On land, cyanobacteria are part of cryptobiotic crusts, which hold sandy soils in place. As a partner in some species of lichens, they fix nitrogen out of thin air. In the water, though, cyanobacteria are becoming more common, and more problematic. The thick film they form on the surface reduces sunlight to plants below. They can clog water filters. And they sometimes, but not always, produce toxins that are harmful to pets, livestock, and humans.
My thoughts strayed back to the red pebble near the shore. Jasper is a form of mineral-stained quartz that once formed as layers within iron ore. I enjoy finding them because they are part of such a unique story. A story, I realized with a jolt, where cyanobacteria play a leading role.
Once upon a time, and by that, I mean 1.9 billion years ago, the atmosphere was filled with carbon dioxide and methane, and the first inklings of life had only just begun. Volcanic activity in the early oceans, and erosion off the few continents, enriched the water with iron and silica.
Cyanobacteria bloomed in those mineral-rich seas, and they also produced at least one type of toxin: oxygen. Free oxygen wasn’t part of the Earth’s early atmosphere, and it was lethal to the first forms of life. At first, the oxygen reacted with the dissolved iron and silica, removing itself from the water by precipitating jasper and other minerals. When cyanobacteria doing photosynthesis pumped out more oxygen than the minerals could remove from the water, though, they poisoned themselves. Boom and bust cycles of cyanobacteria, plus other seasonal and erosional events, resulted in bands of iron-rich rock with different colors, textures, and thickness. Conditions on Earth have changed so much over millennia that this type of rock may never form again.
Like me learning the new skill of paddleboarding, cyanobacteria eventually evolved enzymes that allowed them to live with oxygen. No longer at risk of poisoning themselves with the element, they proliferated wildly, their oxygen waste sweeping most of the iron and silica out of the ocean water for good. Then excess oxygen, no longer tied up with iron, escaped into the air, and began creating the atmosphere we enjoy today.
It's a little ironic, then, that one of the issues with cyanobacteria on the modern Earth is that when they die, sink to the bottom of a lake, and decompose, they deplete the oxygen that life now requires.
A few days after that soupy paddle, the Halloween snowstorm stirred up the lake, and the red jasper at my landing disappeared. The storm waves also dispersed the cyanobacteria, at least until next summer. Over the course of Earth’s history, these little beings have played many roles. Were they heroes for giving us oxygen? Are they villains for gumming up our lakes? Maybe they are simply one part of a long and complicated story.
Emily’s award-winning second book, Natural Connections: Dreaming of an Elfin Skimmer, is available to purchase at www.cablemuseum.org/books and at your local independent bookstore, too.
For more than 50 years, the Cable Natural History Museum has served to connect you to the Northwoods. The Museum is open with our brand-new exhibit: “Anaamaagon: Under the Snow.” Our Fall Calendar is open for registration! Follow us on Facebook, Instagram, YouTube, and cablemuseum.org to see what we are up to.
Last Update: Nov 13, 2024 7:49 am CST
