Natural Connections: Stinky Stonewort – Tomahawk Leader Newspaper


By Emily Stone

Naturalist/Educational Director, Cable Natural History Museum

“Can’t you feel that?” Cade asked from the bow of the canoe. A warm breeze tickled the back of my neck and chased every smell away from me. He had brought a small piece of an aquatic plant with a structure similar to the bladderwort leaves I recently examined. The central green stem bore whorls of thin leaves.

As Cade placed curiosity on the blade of my canoe paddle, the breeze swirled and I caught more than a whiff of sulfur. “It’s chara! ” he stated.

Also known as musk or skunk grass due to its strong smell, chara is a type of algae that grows in clean, hard water with a high pH and lots of minerals. These conditions are rare in the igneous bedrock and glacial sands so prevalent around Cable. Acid bogs or brown-tinged lakes with tannic acid are much more common here. But my bedrock maps show the possibility of nearby dolomite, a calcium-rich rock similar to limestone. We knew we were exploring somewhere special.

The last time I saw chara was in another special place: Alaska. When I accompanied four young geologists taking sediment cores from the bottom of Lake Kelly on the Kenai Peninsula, we found bands of pale “marl” deposits as well as gray-brown silt.

Chara is a type of algae that creates both a calcium carbonate crust and stinking sulfur during photosynthesis. Photos by Emily Stone.

On the scientists’ sampling raft, I pulled out a small bottle of 10% hydrochloric acid that was left over from Professor Tom Fitz’s rocks and minerals course in college, and dropped a few drops on a strip of marl. Bubbles burst. “Crazy fizzer!” I exclaimed. The acid reacted with a base, the same way vinegar and baking soda make mini-volcanoes. The base was calcium carbonate taken from chara corpses a long time ago. Read more about this Alaskan adventure in my blog post titled “Masters of Mud” (

Stonewort is another name for chara because mineral deposits form on its stems as a byproduct of photosynthesis. Much like the acid I dropped on the marl, the chara itself pumps hydrogen ions (which produce acidity) into the water, where they react with the calcium bicarbonate and release carbon dioxide. carbon, which the plant uses for photosynthesis.

Another series of reactions in calcium-rich water (this section is intentionally vague; please note that I haven’t taken a chemistry class since high school) results in the deposition of calcium carbonate on the surface of the chara, which which makes it rough and grainy. If allowed to dry out or decompose, chara becomes ashy and gray.

Sometimes calcium phosphate is formed as part of the processes, which locks in phosphorus that could otherwise fuel the blooms of harmful algae and phytoplankton. These would compete with chara for sunlight. Humans also generally prefer very clear water where chara grows to somewhat muddy water that often results from phosphorus pollution.

Another side benefit of having chara in your lake is that it seems to interfere with the development of mosquito larvae. In a 1928 issue of the Journal of Tropical Medicine, R. Matheson and EH Hinman published an experiment they conducted with mosquitoes and chara in aquaria. They found that adding powdered chara to aquariums killed a significant percentage of mosquito larvae, and they hypothesized that the high pH of chara had something to do with it.

Curiously, in 1929, the same guys discovered that dead or dying chara had no impact on the development of mosquito larvae in their aquariums. They found that the vigorously growing chara caused the death of all introduced mosquito larvae. Matheson and Hinman speculated that high oxygen or low nutrient content could be the problem. Cade and I wonder if those hydrogen ions or the smelly hydrogen sulfide might be at work as well.

Looking at my pictures of the chara, another quirk stood out. Some of the whorled stems had small red-orange appendages. Wikipedia tells me these are antheridia – much like the anthers of plants – the male reproductive structures. A fertilized egg forms an oospore with a hard, mineral shell. With spiral ridges on an oval shape, the oospore resembles a mini foam soccer ball. These fossilize easily and provide a record of past habitats and climate for anyone wishing to bring them to the surface in a sediment core.

Red reproductive structures called antheridia are often visible among the leaf-like stems of chara.

As Cade and I circled the pond, our paddle strokes brought on more of the skunkgrass smell. My underwater camera revealed that diatoms – a smaller type of algae – were growing in a golden film on all chara surfaces. Thick beds of chara rose high enough to break the surface at one end, and there we found dozens of snails, a newt and other critters hiding in the mass of stems.

Last week, I asked what new mystery I would uncover the next time I went to explore a swamp. This week we followed our noses and found chara. Next week…?

Emily’s second award-winning book, Natural Connections: Dreaming of an Elfin Skimmer, is now available for purchase at and at your local independent bookstore as well.

For more than 50 years, the Cable Natural History Museum has connected you to the Northwoods. The Museum is now open with our exciting Growing Up WILD exhibit. Follow us on Facebook, Instagram, YouTube and to see what we’re up to.


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