Sunday, February 21, 2016

Snow Melt

Weather: Sun directions changed, so it's shining in my eyes through a different window around 7:15 am. People have been out on warm days burning weeds in fields and along fences. Last slight snow 2/3.

What’s still green: Juniper, other evergreens; leaves on yuccas, grape hyacinth, garlic, hollyhock, winecup mallow, anthemis, golden hairy asters, most low or buried; pampas grass. Cheat grass coming up along the roadsides, garlic chives coming up.

What’s blue-green or gray: Leaves on Apache plumes, four-winged saltbushes.

What’s red or purple: Stems on roses, young peaches, sandbar willows; leaves on coral beard tongues, alfilerillo, purple asters.

What’s yellow or brown: Arborvitae, stems of weeping willows.

What’s blooming inside: Zonal geraniums, aptenia.

Animal sightings: Rabbits, small birds.

Weekly update: Snow’s still visible when I look south toward the Jémez where I see the more northerly faces. I see less when I look directly across the river. That same area has streaks of white when I look at it from farther north when I’m in town.

As I watch the slow dessication of the snow fields I think about the final retreat of the glaciers that began around 19,00 years ago in Europe. Ice had buried vegetation for years. Moving rocks had removed any vestiges of top soil and left gouges that became mires, bogs, and kettle lakes. Denise Leesch’s team believed, the first plants had to be "capable of growing on mineral soils."

Mammoths moved north through the newly exposed Swiss plateau, but were gone when relative cold returned in the Oldest Dryas that lasted from 17,050 years ago to 14,650. Early in that period, reindeer were hunted. They’re the only ruminants that can live on lichens. In the later millennium, horses and ptarmigan were more common. The latter, a form of grouse, eat birch and willow buds in today’s arctic.

The plateau is rather like our valley, though it has a very different geological origin. On the southeast side are the Alps, which like the Sangre, were uplifted, then eroded to cover the plateau. On the northwest side are the Jura Mountains. Unlike the Jémez, they are limestone. The same calcareous rocks also overlay the Alpine skeleton. During the Pleistocene, granite and gneiss were left in the moraines that marked the boundaries of glacial advances.

Betula nana, which still grows in the far north of Europe, was adapted to the still barren landscape. Insects existed, but not ones that pollinated woody shrubs. The three-foot high birch was pollinated by the wind, which also dispersed its seeds.

Earthworms, which add calcite that neutralizes soil, hadn’t return. The tree grows on acid soils. During the summer, it stores nitrogen and phosphorus in its roots, so that it can feed its own new growth the following spring.

The nitrogen its roots stored probably wasn’t there when the glaciers receded. It was deposited by other plants that didn’t produce pollen. Betaproteobacteria combine ammonium in the soil with oxygen from the atmosphere to produce nitrite. Cyanobacteria capture nitrogen from the air and store it with carbon and phosphate. Because the microbes lack a waxy outer skin, these nutrients leak into the soil.

Cyanobacteria, which is a generic term for a group of species, are the dominant life form in "cold polar environments such as ice shelves, glaciers, glacial meltwater streams and ice-capped lakes," according to Warwick Vincent. They also inhabit the surfaces of rocks, and fissures within them. His team noted they colonize moraines and permafrost soils from those locations.

In water they form mats, with different species living at different levels. On land, they form a dark crust that encourages mosses. When the moisture disappears, they go dormant and merge with the dust. As soon as water reappears, they resume respiration. Within 30 minutes they begin photosynthesis.

Over time, the mosses and bacteria coalesce into more complex communities of lichen, in which the larger plants provide shade that preserves water, while the smaller ones provide sugars for their protectors. Many lichen attach themselves to rocks where the root-like hyphae of the moss penetrate the surface, breaking granite into its constituent parts. They also secret carbonic acid that dissolves granite. The cyanobacteria exude oxalic acid that dissolves limestone.

Jie Chen’s team looked through studies of different types of lichen colonies to estimate the time they took to weather rock. The group found one report from Antarctica suggested colonization began within 40 years on cement, a form of limestone. They found another that suggested it took nearly 10,000 years for a plant community to fully cover sandstone. The last Pleistocene thaw took 7,300 years, enough to create preliminary soils for the Holocene that began 11,700 years ago,

Belnap, Jayne, Julie Hilty Kaltenecker, Roger Rosentreter, John Williams, Steve Leonard, and David Eldridge. Biological Soil Crusts: Ecology and Management, 2001.

Chen, Jie, Hans-Peter Blume, and Lothar Beyer. "Weathering of Rocks Induced by Lichen Colonization - a Review," Catena 39:121-146:2000.

Hendrix, Paul F. Earthworm Ecology and Biogeography in North America,1995.

Leesch, Denise, Jérôme Bullinger, Werner Müller, and Ebbe Nielsen. "The Magdalenian in Switzerland: Re-colonization of a Newly Accessible Landscape," Quaternary International 30:-18:2012.

Preusser, Frank, Hans Rudolf Graf, Oskar Keller, Edgar Krayss, and Christian Schluchter. "Quaternary Glaciation History of Northern Switzerland," Quaternary Science Journal 60:282-305:2011.

Tollefson, Jennifer E. "Betula nana," 2007, in United States Forest Service, Fire Effects Information System, available on-line. I couldn’t find comparable information on the Salix retusa that was dominant at Champréveyres and Monruz.

Versteegh, Emma A. A., Mark E. Hodson, Stuart Black, and Matthew G. Canti. "Pleistocene and Holocene Temperature Reconstructions Using Earthworm-produced Calcite," Geochemical Society and European Association of Geochemistry, Goldschmidt conference, 2013.

Vincent, Warwick F. "Cyanobacterial Dominance in the Polar Regions," in B. A. Whitton and M. Potts, The Ecology of Cyanobacteria, 2000.

_____, Frédéric Zakhia, Anne-Dorothee Jungblut, Arnaud Taton, and Annick Wilmotte. "Cyanobacteria in Cold Ecosystems," in R. Margesin, F. Schinner, J.-C. Marx, and C. Gerday, Psychrophiles: from Biodiversity to Biotechnology, 2008.

Photographs: Crust and moss taken on the prairie; 2010 was a particularly good year for them.

1. Close up of moss in its green and brown phases, 13 March 2010.

2. Crust in its dormant black phase, 21 March 2010.

3. Green just beginning to appear as snow recedes, 19 February 2010.

4. Green and brown moss with black crust, 28 March 2010.

5. Close up of moss and crust, 13 March 2010.

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