Category Archives: Earth Science

The Nuclear Option for Dragonflies

By Bryan Pfeiffer

anax-junius-flight-860x550

A Common Green Darner (Anax junius) / © Bryan Pfeiffer

On a crisp, sunny day in September, after what was probably a typical summer for a dragonfly (which involves flying around, killing things and having sex beside a pond), a Common Green Darner took off and began to migrate south. As it cruised past the summit of Vermonts Mt. Philo, with Lake Champlain below and the Adirondacks off in the distance, the dragonfly crossed paths with a Merlin.

The Merlin, a falcon that kills in flight, swerved, plucked the dragonfly from the sky with its talons and began to eat on the wing. As the falcon and its prey continued southbound, all that remained in their wake was a single detached dragonfly wing, falling like an autumn leaf toward fields at the base of Mt. Philo.

Eagles, hawks, falcons and Monarch butterflies aren’t the only migrants moving south past mountains this fall. Joining them are dragonflies. Although biologists know plenty about the fall raptor and Monarch migrations, we are only beginning to discover, with some creative chemistry, where these dragonflies go and how migration figures in their conservation.

Fly or Die

Most dragonfly species do not migrate. In fact, most are now dead, having already mated during the summer season, leaving behind eggs or larvae to survive the winter. The killing frost will finish off much of what’s still on the wing. But some survivors will leave.

Wandering Glider (Pantala flavescens) / © Bryan Pfeiffer

Wandering Glider (Pantala flavescens) / © Bryan Pfeiffer

Among the 460 or so dragonfly and damselfly species native to North America, at least five are classic migrants: Common Green Darner (Anax junius), Black Saddlebags (Tramea lacerata), Wandering Glider (Pantala flavescens), Spot-winged Glider (Pantala hymenaea) and Variegated Meadowhawk (Sympetrum corruptum). Each species is on the move this fall.

Dragonflies migrate for the same reasons other animals migrate: to avoid inhospitable conditions, in this case habitats that freeze or become too cold for the dragonflies themselves or their insect prey. Monarchs go to Mexico. Broad-winged Hawks leave for wintering grounds stretching from southern Mexico into South America. Dragonflies head south to who knows where.

Having studied birds for two centuries, biologists know well their breeding and wintering distributions , even to the point of learning the destination of a particular warbler or sparrow after it leaves us in the fall. Ornithologists catch lots of songbirds in nets and place around one leg a tiny silver bracelet embossed with a unique number – an avian social security number – and then release the birds to the winds. A small percentage of them, still sporting their bracelets, are later recaptured while in migration or on wintering grounds thousands of miles away. Better yet, we’re putting small electronic transmitters on large birds, such as Bar-tailed Godwits and American Woodcocks, and tracking their movements real-time with satellites.

On of my tagged Monarchs before heading off toward Mexico.

A tagged Monarchs before heading off toward Mexico.

We can even track the movement of a single butterfly. I myself have placed little stickers, each bearing a unique alpha-numerical code, on the hind wings of more than 1,000 Monarchs here in Vermont and elsewhere in North America, and then set each one free to fly toward Mexico, where many are later encountered by conservationists searching for the buttterflies once they arrive in Mexico. With each recovery, we learn more about Monarchs and how they migrate.

The “Heavy” Hydrogen

Dragonflies aren’t so obliging. For one thing, we’re clueless about where they go. Monarchs concentrate each winter in stands of Oyamel Fir in mountains west of Mexico City. So we know where to find them and how to protect them. Tagging or somehow marking a dragonfly would be like putting a message in a bottle and tossing it out to sea. Actually, I suspect we’d find the bottle before the dragonfly.

Yet it turns out that we need not tag or otherwise mark these migratory dragonflies because they themselves carry clues about where they have been. If the Merlin doesn’t get it first, we can catch any migrating dragonfly, analyze trace elements in its tissue and determine roughly how far it has flown.

Our marker is water, more to the point the two hydrogen atoms in water. Recall from high school chemistry that hydrogen nucleus normally contains a single proton and no neutron. But a tiny fraction of hydrogen atoms around the world carry one proton and one neutron. We call it “heavy hydrogen,” or deuterium. And unlike other such atomic variations among elements (which can be radioactive), deuterium is stable in the environment – a “stable isotope”– and stable in the wing of a dragonfly.

isoscape

Credit: Migratory Dragonfly Partnership

The amount of deuterium in water varies somewhat predictably in North America. You can map it. The ratio of deuterium to hydrogen in water falling as rain or snow changes on a gradient corresponding roughly with latitude. Water in Alberta, for example, carries a different deuterium-to-hydrogen ratio than water in Alabama.

Because dragonflies grow up as nymphs in water, they incorporate the local deuterium ratio into their tissue. It’s like a dialect or an accent that a dragonfly bears for life – whether as a nymph in water or a free-flying adult in migration. A Common Green Darner on the wing over Mt. Philo or Miami unwittingly carries a particular deuterium ratio, a birth certificate that tells us generally where it grew up. You are what you eat – or drink.

This science isn’t perfect. We can’t pinpoint a dragonfly’s natal waters in the way we know where a banded bird hatched or a tagged Monarch emerged. But stable isotopes are helping us track the range of migrating dragonflies. It’s “better living through chemistry.” After all, we can’t really know a bird or butterfly or a dragonfly – and what it might need in the way of conservation – until we know all the places it lives or wanders.

By the way, you need not be a chemist to help track dragonfly migration. We’re counting dragonflies in the same way we count migrating raptors during hawkwatches each fall. Learn how to do it and report what you find with help from the Migratory Dragonfly Partnership.

And while we’re out there counting, if a Merlin happens to catch a dragonfly first, we can still make a difference … by catching one of those dragonfly wings floating toward Earth.

Bryan Pfeiffer is a writer and field naturalist who specializes in birds and insects. He teaches writing in the University of Vermont’s Field Naturalist and Ecological Planning Programs.

Before It’s Gone, A Primer on Snow

By Maddy Morgan

Any skier or snowboarder knows that snow does not come in just one form.  Snowpacks are as variable as the snowflakes that form them.  We have all heard the claim that Eskimos have dozens of words for snow (actually, I discovered, just more flexibility in how root words are modified), but what about our terms for snow?  Skiers talk about corduroy and corn snow, but the variation in snow types extends beyond the ski slopes. 

601124_677097335993_631112764_nHere is your late-in-the-season glossary of snow.  Maybe your optimism tells you that the snow won’t be with us much longer, but it might be in your best interest to brush up, just in case.

Snow forms when the atmospheric temperature is at or below freezing.  In certain conditions, it is even possible for snow to reach the ground when the ground temperature is 41 degrees Fahrenheit.  Freezing atmospheric temperatures, combined with moisture in the air, forms snow crystals.  Snow crystals exist in four forms: snowflakes, hoarfrost, graupel, and polycrystals.

  • Snowflakes, which we are all familiar with, are clusters of ice crystals that fall from clouds.  Their shape is dependent on the conditions in which they are formed and through which they fall.
  • Hoarfrost is our name for ice crystals that form on small surfaces that are open to the air.  When a surface’s temperature is lower than the frost point of the surrounding air, moisture transforms directly from vapor to solid, forming delicate laces of surficial ice.
  • Graupel is the round, pellet-like snow that resembles a softer hail.  When ice crystals fall through super-cooled cloud droplets (which remain liquid although they are below freezing temperatures), the droplets freeze to the crystals, forming a clump.
  • Polycrystals are flakes made up of many individual crystals.

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A “Solst-Ice” Report: The Season’s First “Big Chill”

DSCN7727By Matt Pierle

In the aftermath of a backwoods Solstice party in Lamoille County we awoke to a small mountain of dishes and no electricity. The longest night of the year had wrapped us in an icy bear hug.

Cold rain followed by dropping temps had frozen everything stiff.  Tree trunks, branches, rocks – anything not moving fast enough to dance off the cold crystalline bonds – was treated to an icy exoskeleton.

As more precipitation came, the ice coats thickened. The substrate for later drops to adhere to grew as the ice put on layer after layer. Classic positive feedback.

Next year’s already-formed buds and catkins, shelf fungi, conifer needles, marcescent oak and beech leaves were all locked inside one-quarter to a full inch of ice. The forest and hill farm landscape performed back-to-back versions of John Cage’s 4’33”.

NPR news from a crank-operated radio reported, “hundreds of thousands of homes and businesses without power in Michigan, New York, and the Northeast”– no doubt a result of trees and frozen limbs coming down on overhead transmission lines. Continue reading

Orion Rising

orionWe all have our routines, those mental checklists we complete to make sure that our day will run smoothly. Some are entirely rational, others seem almost ridiculous, but all are part of what makes our own worlds go around. One of my self-affirming habits each winter evening is to look for Orion, to make sure that his giant frame is poised for battle in the night sky as he has been since the ancient Greeks raised his mortal body into the heavens almost 3,000 years ago.

Orion’s nighttime traverses actually began long before the Homer immortalized his character in The Iliad. The configuration of the constellation has been visible from Earth for about 1.5 million years and should stay recognizable for about 1 to 2 million more years. Ultimately, the stars will rotate within our galaxy and change their relative positions to each other, as well as to Earth. In the current wintertime sky, Orion routinely rises in the south to southeast at sunset, big and broad, early enough to entertain those of us who aren’t night owls. Betelgeuse, the supergiant that is his right shoulder, is by far the reddest object on the dark horizon and holds the allure that it may explode at any moment, collapsing under its own weight and rebounding into fiery supernova glow. The odds that this impressive event will occur tonight are “astronomically small,” but it is always worth another look.

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Reflections

Sundogs over Huntington, Vermont.

My third-floor office is a commanding venue for a nap.  Reclined in a worn swivel chair with my unsheathed feet stacked on the heat grates, I slip into my best unproductive hours.  When my eyes deign to open, the scenery is ripe for a Chamber of Commerce brochure.  The golden chapel domes and brown brick mortar of the university sit regal and prim before the white speckled ribs of New York and the glass pool of Champlain.  It’s plain lovely.  Especially on biting cold mornings, near 10:00, when some change of guard ushers students out from every academic pore to wade the gray salty paths to their next nook.  It’s one vain pleasure up in my aerie, watching without sympathy the cold scholars scurry. Continue reading

Rock: The Best Thing about Vermont

by Becky Cushing

I’m not a geologist, but recently I learned a thing or two about Vermont bedrock that bumps it above maple syrup or cheese on Vermont’s “Best of” List.

By nature, I ask a lot of questions: What trees are those? How deep is this soil? What bird lives in that nest? Turns out, a lot of the answers are directly or indirectly related to the kind of rock below. And in Vermont, those are calcium-rich rocks—which create an alluring hotspot for many cool, rare or economically important plants.

Picture Vermont 500 million years ago, covered by a vast ocean full of planktonic organisms—a primordial soup. Over time, generations of these tiny organisms died and their bodies drifted to the seafloor laying down sediment full of calcium. When the land shifted and the ocean receded, these compressed sediments formed the basis for the calcareous bedrock of today’s Champlain Valley, mostly dolostone.

So what’s the deal with calcium? Plants need it for metabolism and structure, just like we do. It also helps to raise the pH of the soil (thus lowering the acidity). The chemistry gets a little complicated—but find enlightenment (like I did) in a bottle of Tums. Calcium carbonate, well-known for soothing heartburn, also neutralizes acidity in soil making it more alkaline. Who cares? Bacteria, for starters. And those rascals are necessary for making nitrogen available to plants. In fact, under acidic conditions many nutrients give plants the cold shoulder—instead they’re hooking up with each other or leaching out of plants’ reach. Where dolostone (or limestone) is close to the surface (thanks to several glaciations and years of other erosive processes) these nutrients are more willing.

Farmers have known this forever and call neutral or alkaline soils “sweet.” Plant biologists know it too. I’m embarrassed to admit it took nearly a semester of botany for me to pick up on the pattern of our field trip locations—calcareous bedrock stared me straight in the eye.

Maidenhair Fern

Maidenhair fern near Gleason Brook (photo courtesy of Ryan Morra)

For instance, check out the Long Trail near Gleason Brook in Bolton, VT. If you park in the lot off of Duxbury Rd. and hike up a quarter mile or so, you will start to see telltale plants of calcium-enriched soils like maidenhair fern, wood nettle, blue cohosh, plantain-leaved sedge and white baneberry (doll’s eyes). Sugar maple, white ash, basswood and hophornbeam dominate the tree canopy while striped maples sit eagerly in the understory. Stay on the trail to find the dense patch of pale touch-me- not, an irregular pale yellow flower, at the base of a steep slope on the south side of the trail. Here the downward movement of soil and nutrients from the upper slope along with the exposed calcareous bedrock create a double whammy of plant nutrient bliss. Scientists describe this type of vegetative community as a Rich Northern Hardwood Forest—sounds fancy but Vermonters are spoiled with this natural community-type in ample abundance.

Wood Nettle

Wood nettle near Gleason Brook (photo courtesy of Ryan Morra)

Vermont’s best-kept secret, dolostone, has broader implications than satisfying curious botanizers. Conservation planners, for instance, can use geologic surveys to identify potential priority areas for rare plants among Vermont’s varying bedrock landscape. If you travel a few miles farther on the Long Trail up toward the summit of Camel’s Hump your heartburn might return—the rock transitions to more resistant igneous and metamorphic rocks resembling the bedrock geology of our neighbors to the east in “The Granite State.” At the summit’s rare (seemingly masochistic) alpine plants thrive under harsh, acidic conditions—yet another botanical treat thanks to the state’s multifarious geologic past. Motley geology begets vegetative diversity.

So, next time you douse your pancakes with maple syrupy goodness, take a moment to thank the nutrient-rich soil conditions integral to the Sugar maple-dominated forest community of Vermont.

And remember the best—and oldest—thing about Vermont is the rock.

 

 

Winding Through the Path of Least Resistance

by Ryan Morra

“Slow down, you’re moving too fast, you’ve got to make the moment last.” Simon and Garfunkel phrased it well. If you look at aerial photographs of the Winooski or Lamoille Rivers in northern Vermont, you’ll notice how dramatically the rivers snake through Champlain Valley with one horseshoe-shaped bend after the next.

The Winooski River

The Winooski River flowing through Burlington and Colchester, VT

The Lamoille River

The Lamoille River flowing through Farifax, VT

Launch your canoe into these rivers and you will come face to face with the phenomenon known in the scientific community as fluvial geomorphology. This phrase has become increasingly familiar to the public in the aftermath of Tropical Storm Irene, where fluvial geomorphologists have been called upon to explain the widespread flooding experienced across the state. But what exactly does fluvial geomorphology mean? It refers to the ability of flowing water (fluvial) to shape (-morpho-) the earth (geo-). To be precise, it is the study of all that (-logy).

Half Moon Cove

Half Moon Cove in Colchester, VT

An easily observable way that rivers shape the earth around it is the formation of the horseshoe-shaped meanders, called oxbows, seen in the Champlain Valley. More curious are the crescent-shaped lakes alongside the river, the most dramatic example of which is Half Moon Cove in Colchester. If your instincts tell you that this U-shaped lake may have once been a part of the Winooski River, you are correct. How it formed river can be explained by first thinking about the path of least resistance for a river.

Paddling down the final stretch of the Winooski in a canoe is a dramatically different experience than trying to navigate the steeper rivers found in the mountains. In the Green Mountains, the steep slope causes the water to flow fast and cut out a straight channel on its way down to Lake Champlain, and there is little need to propel yourself along (adrenaline junkies will still find cause to do so, however). Once the Winooski reaches the Champlain Valley, it begins to follow a far more convoluted path, and it is hard to go anywhere in your canoe without paddling.

The soils in the valley are soft clays, silts, and sands that provide little resistance to the now slow-moving river, so the river will bend around at even the slightest obstacle. Once a meander has developed, a feedback process begins that causes further erosion and meandering. Along the outer edge of a curve, the water moves faster than the water on the inside of the curve, since the water must travel a greater distance in the same amount of time. The water erodes the banks along the fast-moving outer edge of the curve, and deposits the silt and sand along the slow-moving inner bends.

If you want to land your canoe during your trip, you will have greater success along these inner bends, where gradually rising sandbars have been built up through this deposition process. Trying to exit on the outside curve of a river bend will prove far more precarious, as the streambank drops of sharply into the river! As the river cuts away at its own banks, it can eventually cut through the remaining bit of land at between the two river bends, and the channel straightens.

Meander Process

How a meander becomes an oxbow lake (source: http://www.geocaching.com/seek/cache_details.aspx?guid=a2541785-59cc-492b-aefb-06ce29e973c6)

Major floods like those experienced after Tropical Storm Irene are sometimes the catalyst for this final step. While we may continue to alter the flow of a river through creating new dams and reinforcing the banks below streamside roads, river waters will constantly look for their path of least resistance, and we may find that our interests are in conflict with the hydrologic forces facing us.  Next time you enjoy a float down the sinewy channels of the Winooski or Lamoille river, note where each bend and twist occurs. When you take your children and grandchildren out in the future, it may not be the same—fluvial geomorphology may have worked its magic.