Hiking With A Field Microscope
Copyright © 2004, Wayne Lanier, PhD
Vernal Pool Fantasies
TABLE OF CONTENTS
Secrets of a San Francisco Deck Garden
Giant Bacteria Found in Golden Gate Park Flowers...!
Cryptobiotic Soil Unearthed in Utah
Revealing Films of Life in a Cliff-side Seep
A Hard Life Out in the Salt Flats
Beneath the Tufas in Mono Lake
The “cover” of this e-book shows a photomicrograph taken from a Vernal pool. The golden diatom moved slowly across the microscope field and collided with the cyanobacterial chain of Anabaena.
Vernal pools and lakes are common all over the United States, and, for that matter, most of the world. The conditions that create a Vernal pool are cyclical: A wet season and a very dry season.
In California, Vernal pools are found on the hot valley plains and in the high Sierra Mountains. In the mountains, the cycle is further complicated by the long, cold winter.
In Navada and Utah, Vernal pools rarely have time to freeze in the high, dry climate. Even if they were to freeze, the ice would soon sublime away. On the Navada Sandstone, they are only ephemeral pools, tiny depressions containing dry sand. A rare rain creates the pool and life must race through its cycles before the water is gone.
I have been observing a Vernal pool in the Sierra Mountains of California for some 10-years. Referred to as “the meadow”, or, sometimes, the “high meadow”, it is a depression near Pole Creek that has no outlet.
As shown in the map on a US Forest Service Tahoe National Forest sign:
Pole Creek crosses Highway 89, and enters the Truckee River about 6-miles from the Sierra town of Truckee, California. An old logging trail runs more-or-less parallel between Pole Creek and Silver Creek and passes by the Meadow about 0.4-miles from its intersection with Highway 89. <>Just after the sign is the Meadow, shown here in June at the height of spring for this 6,000-ft elevation:
I dropped my pack and set up my field microscope near the large tree shown on the left:
Mountain meadows frequently form Vernal pools, or even small Vernal Lakes. The name “Vernal” comes from spring, and the spring flowers that often surround Vernal pools in their spring season.
Much of the California high country was shaped by glaciers. As these glaciers receded, about 10,000-years ago, they left behind depressions that formed lakes or ponds with no outlet. As runoff from the slopes deposited minerals and detritus in the depression, the lake or pond bottom became increasingly biologically productive [REF 1].
Typically, these shallow ponds or lakes undergo a seasonal cycle of succession. During the winter months, the pond is frozen solid under accumulating winter snow.
Winter in the Sierra Mountains is long and cold. Snow at this elevation [6,000-ft] often reaches 15-feet depth and spring may not arrive until May.
As the snow on the slopes melts in the belated spring, the thawing meadow become a pond of some size, surrounded by thick green marsh grass. In this meadow pond, a family of Mallard ducks has taken up residence every spring for the last several years.
Almost overnight, life in the pond quickens. Pond scums and other algae appear. Sedges, rushes, and horsetails ring the pond shallows. Wild flowers of spring – which give the name “Vernal pool” - spring up, beginning with the Sierra corn lilies. Tadpoles appear,
mature into frogs, leave the pond for the shallows or wet grass, and are replaced by dragon flies.
By late July and early August, the pond is shrinking. Increasingly, open water is replaced by meadow grass.
The last remnant of the pond is a small pool at the west end.
By September, even this tiny puddle is gone. The pond has become a brown, grassy meadow, the corn lilies of spring are dry husks.
The tiny puddle has become part of the dry, cracked mud that first diminished the pond circumference, then erased the pond.
Digging into the mud reaches damp clay only some 8-inches down.
And so the meadow will remain until the autumn rains and melt from early snows bring back a much reduced and late season pond. Only the center fills. It is too late. These rains turn to snow and soon the remaining few inches of water stays frozen all day.
The Vernal pool has come full
cycle and, within a few days, will be buried beneath the snows. Winter
will last 5-months, almost half the year.
This cycle of seasons and moisture regulates and sets the parameters within which microscopic life must survive.
Spring Samples
An adult bacteria-eating nematode, probably hermaphroditic.
A Cyanobacterial filament.
Micrasterias, a desmid.
Colony of Anabaena, with close-up of one filament.
Summer Samples [to be added]Fall Samples [to be added]
My base for these studies is the Briscoe family cabin at the intersection of Pole Creek and the Truckee River. Recently, we had a visitor stop by just before we arrived.
Likely a male, this fellow probably topped my weight by a factor of five. Some years ago I believe I met him, his sister, and his mother.
We were awakened about 2:00 AM by someone stumbling about on the back deck of the cabin. Mary Helen's niece had mentioned she might come up to the cabin, so I went to the door and opened it. I found myself nose-to-neck with a female black bear standing on her hind legs with her head nearly a foot above my 6-feet-2-inches. She was trying to get into the storeroom where we had put the remains of a smoked salmon we had for dinner.
I looked at her. She looked at me. Without thinking, I said, “Get out'a here...!” Appearing somewhat exasperated, she dropped down on all fours and ambled away, glancing back only once. With her scurried the round black form of a yearling cub. Mary Helen gave me a pan and spoon, which I beat loudly. A second cub scurried down from a tree next to the deck and raced after mother and sister.
According to the National Forest folks, it has been more than one-hundred years since a human was reported seriously injured by a black bear. Unfortunately, these benign giants have learned to beg, scavenge human trash cans, and break into cabins to steal carelessly-left food. They are not tidy visitors. It has not been one-hundred years since a bear was seriously injured by a human. City folks, unaccustomed to encountering bears, tend to shoot first [or demand that the local police shoot first] and ask questions afterward. In spite of this ill behavior, the black bear population has remained more-or-less steady, while the human population has gotten out of control.
Mary Helen and the grandkids saw one of the cubs about a year later. He was considerably grown and stopped by to check out our barbecue pit, then smoking another salmon. One of the dogs chased him off, but not before he mangled the ice chest in a futile attempt to help himself to a Coke. He sat about half-way up the slope from the cabin, picking grubs out of a rotting log, waiting patiently for the humans and dogs to leave.
Winter SamplesVirtually every resident of a Vernal pool has mastered the art of cryptobiosis. This is easily demonstrated by digging up a sample of the frozen mud from under the ice and letting it stand in the warm cabin overnight. In less than 24-hours, rock-hard frozen mud yields life.
Two diatoms from frozen mud
at the bottom of the Vernal pool in December.
Two photomicrographs were combined. I broke the ice over the meadow and dug up a sample of frozen mud and ice. This sample was “incubated” overnight in the cabin, and examined the next day, after about 18-hours at cabin temperature with some three hours in morning light. Both of these diatoms were active, the pair on the right apparently having divided.
Centric diatoms, of the class Coscinopiscophaceae, are radially symmetrical.
Pond life triumphs, even in the dead of winter.
REFERENCES
1. Bakker, Elna (1984) An Island called California – An Ecological Interoduction to its Natural Communities. University of California Press, Berkeley, 2nd Edition. 488-pp. Paperback, $18.95. See Chapter 13. Mountain Meadow.