Check out Nina Munteanu's blog for a charming tale about a tardigrade, blending some science facts with her fiction! Here's the link at https://themeaningofwater.com/2022/12/25/a-tardigrade-christmas-a-different-christmas-story-with-a-nod-to-lewis-carroll/
Happy Christmas and other good wishes of the season to all!
[Ever wonder what makes foam on the surface of streams you know aren't polluted? You'll learn all about this natural foam, in today's post by Nina Munteanu]
On a late July morning, I was on my daily walk along the Otonabee River in the Kawarthas when I noticed a yellow-brown creamy film on the water lapping onshore. In some places it looked like left over dishwater, but in others, it resembled cream. The multi-hued film swirled like flowing paint in an Emma Lindstrom artwork. It was the “eddy shedding” patterns of Saturn’s north polar atmosphere or Jupiter’s Great Red Spot.
Otherworldly. But it didn’t end there…
Later in the day, the froth turned into a mocha-coloured micro-foam that resembled the crema of a well-made espresso. Entrained by the wind that conspired with the river’s current, the film grew into caramel ropes that covered the rocks on shore in stripy shades of delicious earthy mocha cream—a synesthete’s dream.
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At
the mouth of one little tributary to the river, foam with hints of
caramel rose in a cloud of froth where the runoff tumbled into the
Otonabee River.
“Crema” Micro-foam on Water Surface
My first thought was crushed diatoms. Diatoms are often the main component of periphyton (attached algae) the dominant micro-community in a riverine ecosystem that provide an important food source and home to a diversity of other life.
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Diatom shapes diagram from AQUALITA public website |
Diatoms are single-celled algae enclosed in shells made of nanopatterned silica and organic compounds called frustules. The glass frustules are hard but porous and etched in decorative markings or bands (rows of pores or alveoli to form striae and interstriae) that are used in identifying the more than 20,000 species. The silica shell protects the diatom from predators and acts as a ballast; the pores give the diatom access to the external environment for things like nutrient uptake, waste removal, and mucilage secretion so the diatom can attach itself to a substrate.
When subjected to great turbulence—such as when the dams along the river suddenly open—the diatoms, along with the fatty acids of associated decaying organic matter, create a ‘soap’ as their glass shells break apart and release lipids and proteins that act as foaming agents or surfactants. Air bubbles are pulled in through the turbulence to produce foam. Because the organic surfactants lower the surface tension of water, the bubbles persist at the water’s surface. The bubbles accumulate hydrophobic substances and the dissolved organic matter stabilizes them and aggregates them as nutrient-dense foam. Like I said: cafĂ© crema. This metaphor isn’t farfetched: in fact, crema—the most prized aspect of a well-made espresso—is created through a similar process when hot water emulsifies coffee bean oils and floats atop the espresso with smooth little bubbles.
Given that the Otonabee River is regulated by several hydro-generating dams and locks to control its flow and provide electricity, it’s not surprising that many of the diatoms in the foam are periphyton that have sloughed off a submerged surface in the sudden turbulence caused by the dam release. You’ve seen periphyton; the slippery brownish, oily-looking felt mats that cover the cobbles and rocks of streams and rivers. Sometimes, they grow bright greenish ‘hair’, most likely one of the three most common filamentous green algae (Spirogyra, Zygnema, and Mougeotia), all of which I’d already observed growing on the river banks in the spring.
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Algae filaments |
Periphytic diatoms are often either tube-dwelling diatoms (e.g. Cymbella, Navicula) or diatoms growing on mucilaginous stalks (e.g. Gomphonema, Gomphoneis). Tube-dwellers and stalked diatoms tend to dominate benthic environments of altered hydrological and thermal regimes downstream of dams. These mucopolysaccharide materials also ‘glue’ everything together into a dense micro-foam.
Excited to see if I was right in my initial assessment, I returned with a small glass jar and sampled some of the tan-brown scum-froth then returned home to the microscope. And I confirmed that most of the scum was a combination of:
detritus (decaying organic material from organisms),
living diatoms and other algae, and
the remains of many broken diatoms
The Diatom Forest
Diatoms adhere to submerged surfaces through mucilage produced between the frustule (the diatom’s outer shell) and its substrate. The form of the mucilage varies and includes gelatinous stalks, pads and tubes. For instance, Cymbella and Gomphonema produce long stalks that attach directly to the surface, allowing them to form a swaying canopy over the lower tier of cells such as Fragilaria vaucheriae, Synedra radians and Cocconeis placentula (think overstory and understory of a terrestrial forest or a marine kelp forest).
As part of the understory layer, diatoms such as Fragilaria vaucheriae and Synedra radians attach to the surface at one end (apical) of their rod-shaped frustules using a mucilaginous pad to form “rosettes” that resemble spiky understory shrubs.
Just like trees, the canopy-forming stalked diatoms effectively compete for available light and nutrients in the water with their vertical reach. They provide the ‘overstory’ of the diatom forest’s vertical stratification. These tree-like diatoms also provide an additional surface for other diatoms to colonize (e.g. tinyAchnanthes settle on the long stalks of Cymbella, just as lichen does on a tree trunk).
The stalked diatom forest acts like a net, trapping drifting-in euplankton, such as Pediastrum sp. and Fragilaria spp., which then decide to stay and settle in with the periphyton community. The mucilage captures and binds detrital particles in both lower and upper stories of the diatom forest; these, in turn, provide nutrients for the diatom forest and additional surfaces for colonization. In their work with periphyton communities, Roemer et al. (1984) found several diatoms (e.g. Diatoma vulgare, Fragilaria spp. Stephanodiscus minutula) entangled in the complex network of cells, stalks, and detritus of the diatom forest’s upper story. They also found rosettes of Synedra radians—like jungle orchids—attached to large clumps of sediment caught by the net of mucilage.
Eventually, ‘overgrowth’ occurs as the periphyton colony matures and grows ‘top-heavy’ with all this networking. The upper story of the community simply sloughs off—usually triggered by turbulence such as when the dams release water. This is similar to a forest fire in the Boreal forest, which creates space and light for new colonization and growth. The dislodged periphyton then ride the turbulent flow, temporarily becoming plankton, and those that survive the crashing waters provide “seed” to colonize substrates downstream.
Amid the many dead frustules, I observed many living diatoms along with green and blue-green algae, rotifers, Protista and bacteria feeding on the detritus. I even saw one amoeba, actively feeding on the nutrient-rich interface of a micro-foam organic bubble.
The Regulated River
The dams on the Otonabee River dramatically affect its aquatic biota by altering hydrology, sediment transport, nutrient cycling, temperature regimes, and the movement of organisms. One of the main impacts of a dam is the change in flow dynamics: intensity, velocity, direction. By their very nature, dams create more lake-like environments (lentic) from a more river-like one (lotic). This forces aquatic communities to adapt from free-flowing, erosional habitats to depositional environments.
Having a less mobile substrate along with increased temperatures and higher nutrients in river sections behind dams will lead to increased biomass of certain diatoms and the proliferation of filamentous green algae (e.g. Ceratophylum, Spirogyra, Zygnema, and Mougeotia—all currently blooming in the Otonabee River along with the diatom forests. All are responsible for taste and odor of the water.
Taste and Odour of the Diatom Forest
In addition to providing hydroelectric power, the Otonabee River is a source of drinking water for the City of Peterborough. Particularly in the warm summer months, Peterborough residents notice that their tap water carries a complex taste and odor with hints of mostly earthy mustiness. This is caused by several volatile organic compounds (VOCs) created and released by benthic algae as secondary metabolites associated with growth and reproduction or in response to age, death or environmental stresses. While not harmful, the T&O compounds are detectable even at extremely small concentrations (e.g. parts per trillion).
The diatom forest provides potentially significant sources of biogenic taste and odor VOCs in a river. When diatoms slough off the top-heavy forest and their frustules break apart—particularly during a diatom crash through some disruptive event (e.g. predation, disease, temperature, photolytic stress, dehydration, chemical treatment, or destructive turbulence such as a storm, dam release, etc.)—the diatoms release oxylipins and polyunsaturated fatty acid (PUFA) derivatives, among other things. Oxylipins carry a fishy, rancid, oily or cucumber odor, caused by unsaturated and polyunsaturated aldehydes (PUAs) and other alkenes derived from the fatty acids. They can also cause a ‘grassy-fruity-floral’ odor. The hydrocarbons, amines, terpenes and sulfides released by the degrading diatom mass may smell like solvent, fuel oil or gasoline, acrid burnt fat, and old tobacco.
Diatom species implicated in these odors include Fragilaria, Synedra, Melosira, and Stephanodiscus among others—all identified in the scum I looked at.
Diatoms use volatile taste and odor compounds to modify cell function (e.g. as antioxidants, pheromones, and autoregulation) and food web interactions (grazer deterrents, inhibitors, toxins against predators, attractants) and in response to stress.
Although the production and release of volatile taste and odor compounds is natural to many river algae (in the process of cell metabolism, growth and eventual death and decay), environmental stresses can escalate and intensify the release of T&O compounds. Organic enrichment and nutrient enrichment of the river from fertilizers and urban runoff create stress by overly increasing the biomass of river algae, leading to blooms and bloom crashes with higher incidence of T&O.
References
Diatoms of North America. 2021.
Munteanu, N. & R. Maly. 1981. “The effect of current on the distribution of diatoms settling on submerged glass slides. Hydrobiologia 78: 273-282.
Palmer, Marvin C. 1959. “An Illustrated Manual on the Identification, Significance, and Control of Algae in Water Supplies.” U.S. Department of Health, Education, and Welfare, Cincinnati, Ohio. 98pp.
Roemer, Stephen C., Kyle D. Hoagland, and James R. Rosowski. 1984. “Development of a freshwater periphyton community as influenced by diatom mucilages.” Can. J. Bot. 62: 1799-1813.
Ross, R., Cox, E.J., Karayeva, N.I., Mann, D.G., Paddock, T.B.B., Simonsen, R. and Sims, P.A. 1979. “An amended terminology for the siliceous components of the diatom cell. Nova Hedwigia, Beihefte 64: 513-533.
Round, F.E., Crawford, R.M. and Mann, D.G. 1990. “The Diatoms. Biology and Morphology of the Genera.” Cambridge University Press, Cambridge. 747pp.
Smolar-Zvanut, Natasa and Matjaz Mikos. “The impact of flow regulation by hydropower dams on the periphyton community in the Soca River, Slovenia. Hydrological Sciences Journal 59 (5): 1032-1045.
by Nina Munteanu
I’m a limnologist (someone who studies water and water systems); I’m also a Canadian, living in the north. That means that the water and waterways I study are often covered in ice and snow.
Since moving to Peterborough a few years ago, I’ve been walking daily along the shores of the Otonabee River, through riparian forest and marsh and small tributaries. The Otonabee River is a regulated river, with several dams and locks, forming part of the Trent-Severn Waterway in the Great Lakes Basin. The Otonabee River, which provides Peterborough its drinking water, receives water from Katchewanooka Lake in Lakefield and flows south through Peterborough into Rice Lake and from there water flows via the Trent River into Lake Ontario.
The Otonabee is regulated through a series of locks and dams with generating stations for electricity. I’ve been enjoying the seasonal changes of the river, along with the ostensible water level changes imposed throughout the seasons by the various dams and diversions. This has been particularly interesting for me during the onset and duration of winter, when ice and snow play a role in the river’s character. When it’s cold enough (at zero degrees Celsius or 32 degrees Fahrenheit), ice forms. It can form as a solid sheet on lakes and rivers and on land (as a glacier). Ice can also occur as frost, snow, sleet and hail.
Limnologists talk about the ice-up of lakes and rivers, often making it sound like a singular phenomenon. But it isn’t. The characteristic ice sheet of a fully frozen lake or river goes through several stages and will vary from year to year. The cyclic nature of ice-up determines the quality and nature of the ice that forms and the under-ice environment. In a regulated river it gets even more complicated.
But it all starts with young ice crystals, frazil ice, that grow and evolve into something bigger.
When Water Freezes & Ice Grows
Two things determine how ice forms: temperature and turbulence. The Otonabee experiences below freezing air temperatures for close to five months of the year and is both turbulent and calm in various places and times based on its level changes. This makes for some varied and interesting ice phenomena.
As early as November, when it’s freezing cold and water supercools, sharp pointed discs of ice crystals (frazil ice) form and mix into the waterbody’s upper layer. The ice molecules expand into an organized latticework that is less dense and lighter than liquid water, allowing it to float. Frazil ice often develops into slushy clumps of white ice a few centimeters across (grease ice or slushy, spongy grease ice called shuga). Frazil and grease ice may also create nilas ice, an up to 10 cm thick elastic ice crust with a mat surface.
On a quiet surface with little wind, such as a protected bay or pond, clear ice forms under very cold weather. Transparent ice may resemble Goethe glass and reflect light like clear wate or it can be slightly cloudy, reflecting a deep or aqua-turquoise blue, depending on the materials the crystals nucleate on. When the ice cover expands from the shore to the entire river or lake, it’s called fast ice because it’s held fast by the shore.
In rougher moving water, ice forms in a less orderly and transparent way, first forming frazil.
In more calm waters of shorelines and inlets, frazil ice may form skim ice that may look like a film of grease. Ice rind, a brittle shiny crust up to about 5 cm thick may form along protected shores around marsh reeds or on exposed rocks.
Ice crystals need a nucleating agent to form in supercooled surface water. Examples include snow and ice fog, or already existing ice (e.g. frazil). Sediment and bacteria in lake and river water can also act as nucleating agents. In moderately cold and calm water with no falling snow, large crystals form unseeded ice; the nucleation sites are most likely particulates in the water. When snow falls, tiny ice crystals form on the water surface (seeded ice).
On a minus twenty C° January day, I followed the frazil or floating slush as it drifted downstream below a dam until the frazil ran into an ice jam that was piling up behind the next dam. Much of the frazil had organized into hundreds of small circular 4-cm diameter wide ice pancakes in the turbulent flow. The tiny pancakes collided into one another and jammed up against the established frazil ice sheet, creating a frazil floc and eventually cementing into the larger ice jam. The small ice pancakes foamed up with a milky froth, sliding on top or below each other and crowding into the ice jam. They made a distinct fizzing high pitched ‘shhh’-sound, just like soda pop when it’s first opened. They were frazilling. Frozen waves of ice fraziling formed and thin shards of broken ice rind had rafted over each other to form rows of hummocks as the ice jam grew upstream from the dam.
Pancake Ice
Pancake Ice is ice that spins around in waves and thickens into free-floating ice disks. It forms particularly where the turbulence of rough water and rapids affect slush or ice rind, such as just downstream of a dam. This is exactly where I’ve seen pancake ice of varying sizes on the Otonabee River (pancakes from as small as 4-centimetres to as large as 3-metres wide and up to 10 cm thick).
Pancake ice forms in two ways: 1) on water covered by slush, shuga or grease ice that, when it becomes sufficiently dense, congeals to form a pancake, or 2) from breaking ice rind, nilas or even gray ice in agitated conditions. When the floating ice rinds of grease ice break up, pancake ice forms from the pieces. I’ve seen pancakes raft over each other, creating an uneven top and bottom surface on an ice jam. I saw good examples of pancake-frazil formation below one dam and these formed an ice jam behind a downstream dam.
The rims of pancake ice are often turned up; when the pancakes collide into each other like bumper cars, frazil ice or slush piles onto their edges.
Glossary of Ice Terms (Environment Canada):
ADVECTION FROST: A collection of small ice crystals in the shape of spikes that form when a cold wind blows over branches of trees, poles, and other surfaces.
BRASH ICE: Accumulations of floating ice made up of fragments not more than 2m across; wreckage of other forms of ice.
FAST ICE: Ice that forms and remains fast along the shore, where it is attached to the shore, an ice wall, or ice front.
FRACTURING: Pressure process whereby ice is permanently deformed, and rupture occurs.
FRAZIL ICE: Fine spicules or plates of ice (ice crystals), suspended in water.
GRAY ICE: Young ice 10-15 cm thick, less elastic than nilas and breaks on swell. Usually rafts under pressure.
GRAUPEL: Heavily rimed snow particles or pellets, typically white, soft and crumbly.
GREASE ICE: A later stage of freezing than frazil ice. It occurs when the crystals have coagulated to form a soup layer on the water surface. Grease ice reflects little light, giving the water a mat appearance. Forms shuga.
HUMMOCKED ICE: ice piled haphazardly one piece over another to form an uneven surface. When weathered, it has the appearance of smooth hillocks.
ICE BRECCIA: Ice of different stages of development frozen together.
ICE JAM: An accumulation of broken river ice caught in a narrow channel.
ICE RIND: A brittle shiny crust of ice formed on a quiet surface by direct freezing or from grease ice. Thickness to about 5 cm. Easily broken by wind or swell, commonly breaking in rectangular pieces.
NILAS: A thin elastic crust of ice, bending easily on waves and swell. Up to 10 cm thick with a mat surface. Under pressure it thrusts into a pattern of interlocking fingers.
PANCAKE ICE: Mostly circular pieces of ice from 30 cm to 3 m in diameter and up to 10 cm thick, with raised rims due to the pieces striking against one another. May form on a slight swell from grease ice, shuga, or slush, or from the breaking of ice rind, nilas or gray ice.
POLYNYA: Any nonlinear-shaped opening in the water but enclosed by ice. Some polynya recur annually in the same position.
RAFTED ICE: Type of deformed ice formed by one piece of ice overriding another.
RAFTING: Pressure processes whereby one piece of ice overrides another. Most common in new and young ice.
SHUGA: An accumulation of spongy white ice lumps, several centimeters across; formed from grease ice or slush and sometimes from ice rising to the surface.
References:
Armstrong, T., and B. Roberts. 1956. Illustrated ice glossary. Polar Record 8:4-32.
Ashton, G., editor. 2010. River Lake Ice Engineering. Water Resources Publications LLC, Highlands Ranch, Colorado, USA.
Bengtsson, L. 1986. Spatial Variability of Lake Ice Covers. Geografiska Annaler: Series A, Physical Geography 68:113-121.
Brown, L. C., and C. R. Duguay. 2011. A comparison of simulated and measured lake ice thickness using a Shallow Water Ice Profiler. Hydrological Processes 25:2932-2941.
Burn, C. R. 1990. Frost heave in lake-bottom sediments, Mackenzie Delta, Northwest Territories. Nordicana 54:103-109.
Cherepanov, N. 1974. Classification of ice of natural water bodies. Pages 97-101 in Ocean '74 : IEEE International Conference on Engineering in the Ocean Environment Institute of Electrical and Electronic Engineers, New York, NY, USA.
Downing, John A. 2021. “Ice Formation is Not a Singular Phenomenon.” University of Minnesota Sea Grant. February 25, 2021.
Eisen, O., J. Freitag, C. Haas, W. Rack, G. Rotschky, and J. Schmitt. 2003. Bowling mermaids; or, how do beach ice balls form? Journal of Glaciology 49:605-606.
Fahnestock, R. K., D. J. Crowley, M. Wilson, and H. Schneider. 1973.Ice& volcanoes of the Lake Erie shore near Dunkirk, New York, USA. Journal of Glaciology 12:93-99.
Kavanaugh, J., R. Schultz, L. D. Andriashek, M. v. d. Baan, H. Ghofrani, G. Atkinson, and D. J. Utting. 2019. A New Year’s Day icebreaker: icequakes on lakes in Alberta, Canada. Canadian Journal of Earth Sciences 56:183-200.
Kempema, E. W., E. Reimnitz, and P. W. Barnes. 2001. Anchor-Ice Formation and Ice Rafting in Southwestern Lake Michigan, U.S.A. Journal of Sedimentary Research 71:346-354.
Knight, C. A. 1962. Studies of Arctic Lake Ice. Journal of Glaciology 4:319-335.
Michel, B. 1971. Winter regime of rivers and lakes. US Army Corps of Engineers, Cold Regions Research and Engineering Laboratory, Hanover, New Hampshire USA.
Michel, B., and R. O. Ramseier. 1971. Classification of river and lake ice. Canadian Geotechnical Journal 8:36-45.
Muguruma, J., and K. Kikuchi. 1963. Lake Ice Investigation at Peters Lake, Alaska. Journal of Glaciology 4:689-708.
Pounder, E. 1965. Physics of ice. Pergammon Press, Oxford, UK.
by Nina Munteanu
It was early winter, before the snows, as I entered the large cedar swamp-forest and felt magic touch my shoulder.
It wasn’t just the deep soggy forest and the twittering birds or the fresh pungent smell of cedar in the air. Or the lanky trees creaking in the warm wind. There was something in the air that stirred my senses. The magic of discovery.
Amid the soft hush of the breeze through the leaves, the tall trees leaned into each other, groaning and clanking like whispering gossips. Moss crept up their widely planted feet. It carpeted the russet duff on the ground with splashes of fluorescent green. Several over two-hundred-year old cedars had fallen and their decaying bodies were feeding a whole new generation of trees. Cedars growing on cedars. I left the path and climbed onto a several metre-wide and twenty-metre long moss-covered cedar corpse. My steps sprang over spongy ground—now a mixture of rich soil, decaying wood, fungus and detritus. I could make out the black fibrous layers of decaying wood beneath a carpet of moss and dead leaves.
I’ve been told that the heartwood of eastern white cedar (Thuja occidentalis) is highly resistant to moisture, decay and insect infestation due to the phytoncides (oils and acids) it produces; it’s these compounds that give off its distinctive pleasant and calming aroma. Many of the compounds are variants of thujone and include alpha pinene, alpha thujone, beta thujone, bornyl acetate, camphene, camphone, delta sabinene, fenchone and terpinenol.
A fallen cedar can remain intact, slowly decomposing on the forest floor for over a century. This is due to its natural preservative that is toxic to decay-causing fungi. Nursery logs provide rich habitat for seedlings to take root and a complexity of growing plants, fungi, liverworts, and other wildlife to thrive in. These ancient trees play a vital role in climate balance. They store two to three times more carbon than second-growth trees. Because of their slow decay, cedars lock carbon in their biomass for a longer period—creating a slow and efficient carbon store. Even dead snags and nursery logs continue to store carbon as they provide habitat for other living things.
Simply walking in a cedar forest can directly boost your health by breathing in its aerosols: cedar oils (terpenes) help boost our immune systems; cedars have anti-oxidant compounds and anti-inflammatory compounds. You also help your well-being by listening to the forest’s curative infrasounds and other frequencies; they help to quiet your mind. The benefits are numerous: from heightened calmness, creativity and problem solving, greater immunity, to a greater sense of general well-being and overall happiness. When you spend time in the forest, you inhale beneficial bacteria, plant-based essential oils, and negatively charged ions.
The eastern white cedar also contains high amounts of vitamin C (50 mg of vitamin C per 100 grams). Because of this, various parts of the tree (mostly leaves and bark) are used in herbal medicine, mainly for their immune-system stimulating effects. When 16th century explorer Jacques Cartier and his men fell ill with scurvy, the native people helped treat them with a tea from this conifer. The tea is made by dropping several small pieces of cedar leaves into water that has just been boiled and allowed to steep for five to seven minutes then strained into a fresh menthol-aromatic tea.
Curious to taste cedar tea, I convinced good friend Merridy to accompany me on my next excursion to my magic cedar swamp forest in the Trent Nature Sanctuary near Peterborough, Ontario. We collected some fresh leaves from a fairly-young tree then upon returning to Merridy’s place, we boiled some water and cut up the cedar leaves, which gave off a refreshing citrus camphor smell. I dropped the fresh leaves into the pot of boiled water and let it steep for seven minutes then poured the light-coloured tea into two cups. The tea was hardly more than water. There was just the hint of colour, no more. I inhaled the tea and took in a very mild scent of cedar. More like a woodsy smell.
Then we took our first sips. We shared our first impressions: “Tastes like cedar,” said Merridy unceremoniously and gave a short laugh. Then she added, “It has a mild delicate taste.” I was pleasantly surprised at the gentleness of the flavour. The first sip took in subtle notes of the forest with an aftertaste of cedar. The second larger sip yielded more robust citrusy and astringent notes of cedar bark and wood. I could detect the sharper complexity of terpines. It was fresh like a forest breeze in springtime. In short, it was delightful.
Despite its beneficial properties, cedar tea should not be taken in excess. One of the reasons is thujone, a volatile monoterpene ketone with a menthol odour, best known as the chemical compound in the spirit absinthe. The eastern white cedar contains an appreciable amount of thujone (hence the tree’s genus name Thuja). This monoterpene can be toxic to brain, kidney, and liver cells and can cause convulsions if taken in too high a dose. Given its interference with certain neuro-receptors, small doses of thujone may convey stimulating mood-elevating effects. The lesson here is that if you drink cedar tea, do so in moderation. Enjoy its beneficial qualities, but respect its other qualities!
A Puffball Treasure
Back in the cedar swamp forest, I was crawling on the spongy ground, clutching my camera to take some close shots of the bright moss that was fruiting in profusion. Before I knew it, I’d stumbled into the dip between two giant decayed logs. There, like Indiana Jones in the deep jungles of Borneo, I discovered my hidden gold: puffballs!
Dozens of them littered the ground, looking like eggs, as though some puffball-hen had laid them. Whitish, round and with a paper-like texture, each plump spore sac pouted with a beaked mouth (peristome) and sat nested in a star-like “collar” (exoperidium) with decorative cracks and fissures. The puffballs resembled a chorus of singers “oohing”. I identified the puffball as a Collared Earthstar (Gaestrum triplex), a saprobic fungus that commonly grows in humus-rich deciduous/coniferous forests amid leaf litter. The puffballs release their spores when the wind blows past the pointed “mouths” or when they are disturbed by rain or animals—like me. Reverting to a childhood inclination, I poked one with my finger and it released a yellowish-green cloud of spores. I clapped my hands with glee and realized that I’d just opened a door to magic.
Then it started to rain. First a light rain that sizzled over the ground and vegetation. Then drumming. And finally pelting. I inhaled the freshness in the air and didn’t mind that I would soon be soaked—my raincoat wasn’t really a raincoat, more like a cheap wannabe. I didn’t mind because the magic was transforming and I was part of it.
With the rain, the greens and russets grew intense. The moss sparkled. The air grew thick with moisture and a mist veiled the forest in soft gossamer. When I looked down at my puffballs, I noticed that the delicate whitish rice-paper spore sacs had transformed into tan-coloured rubber balls that sprang back like pressurized balloons if poked. I would never have imagined this and found myself grinning in the magic of discovery.
Just as I made to leave this magical cedar swamp forest, I caught sight of what looked like an errant wandering puffball on top of one of the ancient logs. Unlike the others whose spore sacs were nestled in an outer collar, this puffball’s spore sac was perched proudly high, atop a series of ‘legs,’ the rays of the outer peridium. The puffball resembled an octopus standing on its many tentacles. I later identified it as another species of Earthstar, the Beaked Earthstar (Geastrum pectinatum), which likes to live under (and on) conifers.
The puffball looked like it was going on walkabout. Perhaps I would join it.
How the Bdelloid Rotifer Lived for Millennia—Without Sex
by Nina Munteanu
As a child, I always wanted a microscope.
I would have collected slimy waters from the scum ponds and murky puddles near my house. I would have brought them home and exposed them to the light of my microscope. I would then have peered deep into a secret world, where shady characters and alien forms lurked and traded.
It would be many years, when I was in college, before I finally witnessed this world—so alien, it might have inspired the science fiction books I wrote later as an adult. As it turned out, I was led to pursue a Masters of Science degree, studying periphyton (microscopic aquatic communities attached and associated with surfaces like rocks and plants) in local streams in the Eastern Townships of Quebec.
While my work focused on how diatoms (glass-walled algae) colonized surfaces, micro-invertebrates kept vying for my attention. Water fleas (cladocerans), copepods, rotifers, seed shrimps (ostracods) and water bears sang across my field of vision. They flitted, lumbered, wheeled and meandered their way like tourists lost in Paris. But this wasn’t Paris; I’d taken the blue pill and entered the rabbit hole into another world...
The Secret—and Dangerous—World of Micro-Organisms
Small freshwater habitats are home to a highly productive and diverse collection of micro-invertebrates—multicellular animals that can barely be seen with the naked eye. Many average from 0.5 to 1 mm in size and resemble little white blobs; however, a scholar can distinguish each invertebrate by its unique movement. For instance, when presented with a jar of pond water, I can usually distinguish among the wheel-like wandering of a gastrotrich, dirigible-like gliding of an ostracod (seed shrimp), the vertical goldfinch-style “hopping” of the cladoceran (water flea) as it beats its antennae, or the halting-jerking movements of copepods (oar-feet) as their antennae drive them along like a dingy propelled by an amateur oarsman.
Alas, puddles, ephemeral ponds and vernal pools pose sketchy habitats, given their tendency to appear and disappear. These environments are ever-changing, unstable, chaotic and unpredictable. Yet, anyone who has studied these ecosystems understands that they team with life.
When a puddle or ephemeral pond dries up then reappears with rain, how can these communities thrive? Do they all die off and then somehow recruit when the pond reappears? Many of these invertebrates have evolved creative ways to survive in very unstable environments. Some form a resting stage—a spore, resting egg or ‘tun’—that goes dormant and rides out the bad weather.
Animalcules & Sleeping Rotifers
Rotifers are cosmopolitan detrivores (they eat detritus) and contribute to the decomposition of organic matter. Rotifers create a vortex with ciliated tufts on their heads that resemble spinning wheels, sweeping food into their mouths. They often anchor to larger debris while they feed or inch, worm-like, along substrates. Some are sessile (attached), living inside tubes or gelatinous holdfasts and may even be colonial. Others move about and may temporarily anchor themselves as they feed. Rotifers include species that alternate sexual reproduction with asexual reproduction, depending on environmental conditions.
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| Bdelloid Rotifer as photographed by Bob Blaylock |
In 1701, Antonie van Leeuwenhoek observed that “animalcules” (likely the bdelloid rotifer Philodina roseaola) survived drying up and were “resurrected” when water was added to them. He’d discovered a highly resistant dormant state of an aquatic invertebrate to desiccation.
Dormancy is a common strategy of organisms that live in harsh and unstable environments and has been documented in crustaceans, rotifers, tardigrades, phytoplankton and ciliates. “Dormant forms of some planktonic invertebrates are among the most highly resistant … stages in the whole animal kingdom,” writes Jacek Radzikowski in a 2013 review in the Journal of Plankton Research. Radzikowski describes two states of dormancy: diapause and quiescence.
Diapausing results in the production of a dormant egg or cyst whose thick envelope or shell protects it from drying, freezing, mechanical damage, microbial invasion and predation, UV radiation and harmful chemicals. Many survive being eaten and can resist vertebrate digestive enzymes, helping them disperse and colonize isolated water bodies. Diapause is controlled by an internal mechanism that is initiated by various cues, such as temperature or photoperiod. In short-lived organisms, it is typically initiated only in a single ontogenetic stage. “Breaking of diapause requires specific cues, and not necessarily the return of favorable conditions,” writes Radzikowski.
Quiescent dormancy does not involve the production of a dormant egg or cyst; rather it involves a transformation of the organism itself into a dormant state through a process called cryptobiosis. “Quiescence is … induced directly by the occurrence of harsh environmental conditions. A quiescent organism can enter this state in many stages of its life, and remains dormant only until the adverse conditions end,” writes Radzikowski.
The All-Female Bdelloid Rotifer
I recently had a chance to study a pond sample in a Petri dish through a friend’s microscope. Attached to a pile of detritus shivering in the current like trees in a gale, were several microscopic rotifers; they were feeding. Their ciliated disk-like mouths twirled madly, capturing plankton to eat. Watching them reminded me of my early research days at Concordia University in Montreal. Probably Philodina (a bdelloid); I had seen many during my stream research in Quebec.
The bdelloid rotifer has dispensed with sexual reproduction entirely and reproduces exclusively by female parthenogenesis. All-female bdelloid rotifers have thrived for forty million years. They’re everywhere, in temporary ponds, moss, even tree bark. Part of the reason for their incredible success lies in their strategy of quiescent dormancy.
In response to unfavourable conditions like a pond drying up, bdelloid rotifers enter a process called anhydrobiosis, contracting into an inert form and losing most of their body water. The bdelloid withdraws her head and foot and contracts her body into a compact shape called a tun; a dormant state that remains permeable to gases and liquids. In this state, bdelloid rotifers can resist ionizing radiation because they can repair DNA double-strand breaks. Early research noted that dormant animals could withstand freezing and thawing from −40°C to 100°C and storage under vacuum. They also tolerated high doses of UV and X radiation. Later work reported that some rotifers could survive extreme abiotic conditions, such as exposure to liquid nitrogen (−196°C) for several weeks or liquid helium (−269°C) for several hours. Dried up adult bdelloid rotifers apparently survived minus 80°C conditions for more than 6 years.
Dormancy is an elegant technique to ride out harsh conditions. The bdelloids can go dormant quickly in any stage of their life cycle—embryo, juvenile or adult—and they’re capable of remaining dormant for decades. They can recover from their dormancy state within hours when the right conditions return and go on reproducing without the need to find a mate.
Research has shown that bdelloid mothers that go through desiccation produce daughters with increased fitness and longevity. In fact, if desiccation doesn’t occur over several generations, the rotifers lose their fitness. They need the unpredictable environment to keep robust. This is partly because they incorporate genes from their environment during anhydrobiosis. When dormant, they acquire mobile DNA and stitch it into themselves through a process called horizontal gene transfer (HGT).
Bdelloid rotifers carry change inside them, through phenotypic plasticity, physiological stress response mechanisms, or life history adaptations. That’s why the bdelloid rotifers survived for millennia and will continue for many more. They are able to keep up with rapid and catastrophic environmental change, not to mention something as gigantic as climate change. They adapt by counting on change.
References:
Munteanu, Nina. 2020. “A Diary in the Age of Water.” Inanna Publications, Toronto. 300pp.
Munteanu, Nina. 2016. “Water Is…The Meaning of Water.” Pixl Press, Vancouver. 586pp.
O’Leary, Denise. 2015. “Horizontal gene transfer: Sorry, Darwin, it’s not your evolution anymore.” Evolution News, August 13, 2015. Online: https://www.evolutionnews.org/201508/horizontal_gene/
Ricci, C. And D. Fontaneto. 2017. “The importance of being a bdelloid: Ecological and evolutionary consequences of dormancy.” Italian Journal of Zoology, 76:3, 240-249.
Robinson, Kelly and Julie Dunning. 2016. “Bacteria and humans have been swapping DNA for millennia”. The Scientist Magazine, October 1, 2016. Online: https://www.the-scientist.com/?articles.view/articleNo/47125/title/Bacteria-and-Humans-Have-Been-Swapping-DNA-for-Millennia/
Weinhold, Bob. 2006. “Epigenetics: the science of change.” Environmental Health Perspectives, 114(3): A160-A167.
Williams, Sarah. 2015. “Humans may harbour more than 100 genes from other organisms”. Science, March 12, 2015. Online: http://www.sciencemag.org/news/2015/03/humans-may-harbor-more-100-genes-other-organisms
