terra central

A Tragic Ignorance of Mineral Weathering

Rainwater harvesting offers a safe alternative to arsenic-tainted groundwater.

Following up on a report from the British journal Lancet, global news agency AFP reports:

“Up to 77 million Bangladeshis have been exposed to toxic levels of arsenic from contaminated drinking water, and even low-level exposure to the poison is not risk-free, The Lancet medical journal reported.

By some estimates, between 35 and 77 million people in Bangladesh have been chronically exposed to arsenic-contaminated water as a result of a catastrophically misguided campaign in the 1970s.”

The “misguided campaign” had the good intention of providing safe water to millions of people living on the vast, low-lying Ganges–Brahmaputra River Delta. The delta receives drainage and sediment from the Himalayan mountains and, due to the wet tropical climate and relative solubility of arsenic-containing soil minerals, the groundwater is contaminated.

Rainwater harvesting is an inexpensive, sustainable alternative to using tainted groundwater for drinking. Expanded use of rainwater harvesting with simple technological enhancements to improve on an ancient practice is showing good results. The problem seems to be difficulty expanding the program fast enough.

Bangladesh, squeezed between the mountains and the sea, and most of which is less than 40-feet above sea level, has the coastal problem of saltwater intrusion into surface freshwater sources. Here is an interesting video on that topic and efforts to build more rainwater harvesting systems.

Further information on Rainwater Harvesting

More Sandbags: Fargo-Moorhead Braces for Major Flood

For the second year in a row, soils, geomorphology, and snowpack set up a major flood risk.

The Red River of the North has “issues” that tend to make life “interesting” for those who live near it and depend on it. The Red is a fairly small river in a large watershed. The Red River Valley is not really a river valley at all, but a broad, flat lake bottom formed by Glacial Lake Agassiz.

The fertile soils of the Red River Valley developed from clayey (smectitic) glacial drift largely derived from the Pierre Shale. These sediments, known as the Sherack Formation, are parent materials for the widespread Fargo silty clay (Fine, smectitic, frigid Typic Epiaquerts). These soils are poorly drained and the high-activity smectite clay shrinks and swells as it wets and dries. The force of the expanding clay soil has no problem cracking basement walls. Excavating around foundations, straightening and bracing basement walls is a good business in Fargo-Moorhead. If you want to sell a house, get ready for a building inspector to tell you to fix your foundation.

Because the Red River flows north, it tends to thaw first at the south end and ice-jam at the north end, causing water to back up at the south end of the valley. Post-glacial isostatic uplift is greater at the north end of the valley, where the glacial ice was thicker, so the valley is gradually tipping north to south, from Pembina toward Wahpeton. As the estimable North Dakota State Geologist John Bluemle writes

Because the amount of uplift was so much greater at Pembina than it was in the south at Wahpeton, the gradient of the Red River has decreased markedly since its route became established. Since Lake Agassiz drained from North Dakota about 9,000 years ago, the Red River has meandered over an increasingly broad floodplain. Flooding is a recurring problem along portions of the Red River.

So, because the diminished river gradient caused by isostatic rebound tends to back water up at the south end of the valley, and ice jams up north partially block river flow, and the clay-rich soils plowed and left bare over the winter let snow melt run off like soup on a plate, Fargo-Moorhead gets ready for another flood.

And the flooded fat clays in the soil will crack more foundations, and the basement walls will crack and leak, and the wall-jacking contractors will have work again next summer.

Summers are real nice out there.

“Stripes:” A Type of Patterned Ground in Gelisols

Photo credit: Thibaut Cheytion (Tibo)

Update: 12-14-2007
Received an email from Tibo, who thinks the stripes might be wind-generated. My first impression of the picture had me thinking dune ripples, as well. The odd thing, seems to me, is the thin mantle of vegetative cover on what looks like smooth dune sand. I wouldn’t expect the shifting dune sands to be stable enough for such a uniform covering of moss, or whatever the plant cover is. It might take a another field trip to solve this mystory. Here is a photo of periglacial stripes taken by someone at the University of Regina Geography Department.

In the world of soil taxonomy, the most recently “minted” soil order is the Gelisol order. Gelisols are found in very cold climates that support permafrost. Two major processes associated with Gelisol formation are solifluction (or gelifluction), and cryoturbation.

Solifluction occurs when the saturated (or nearly so) upper part of the soil thaws in summer and flows over the top of the permafrost below, creating low ridges and swales that look like “stripes.”

Since the volume of water expands about 10-percent when turned to ice, cryoturbation is a process of soil mixing, heaving, and buckling due to freeze-thaw cycles. Sometimes frost thrusting creates polygons, such as those shown in the valley here in an earlier post.

The photo above was taken by Thibaut Cheytion (Tibo), a young MBA and CFO of a company in China. Whether he knows it or not, he’s got an eye for soil geomorphology. This photo, I think, shows an especially beautiful example of patterned ground.

Because organic decomposition is slowed by cold temperatures, Gelisols are generally high in organic matter and, therefore, an important global carbon sink.

Soil at the Center of the Environment: Part 1

Photo Credit: High Agriculture by Thibaut (Tibo) Cheytion

Soil is an open and dynamic system and supports all terrestrial life, and to a large extent, by providing nutrients in solution, supports aquatic and marine life, as well. This is evident in the high biological productivity found in estuaries, places where rivers meet the sea.

Soil stands at the crossroads of the earth’s vital spheres: the lithosphere (crust of the earth), the atmosphere, the hydrosphere, and the biosphere. All of these “spheres” intersect at the soil.

The soil is derived from the rocks and minerals of the local lithology, or from sediments naturally transported by various means from elsewhere. Lithology leaves a chemical and textural signature on the soil that develops over time, affecting everything that subsequently grows in the soil.

Water moves into the soil from above as precipitation, from below as groundwater, from the sides as seepage from surface water bodies. The soil may release water to all of these places in different ways.

The soil is the “breathing organ” of the earth, cyclicly exchanging gases with the atmosphere.

Soil serves as structural foundation for land plants. Animals, microbes, and fungi living largely unnoticed in the soil carry out complex
biogeochemical processes in plant root zones, making nutrients available to growing plants, and releasing agents of chemical weathering to the soil.

Considering all it does, one might think the “humble soil” of the earth deserves a more sophisticated name, and it does. It is called the pedosphere, the part we touch with our feet.

A note about the photo taken by Tibo, who’s an economist, in Tibet: There are several alpine glacial and periglacial landforms well represented. There are perhaps five aretes, which are straight, sharp ridges between or adjacent four bowl-shaped cirques carved into the sides of the mountains. There is also a U-shaped valley. The relatively young soils supporting crops in the valley look like they are atop ice-wedge poygons derived from glacio-fluvial sediments that are often saturated and undergo frequent freeze-thaw cycles. Polygons are one type of “patterned ground” found near alpine and continental glaciers. Photo used with Tibo’s generous permission.