Monroe County: Cottonwood Pits

cottonwood aerial
The old mine pits almost look like landing strips for waterfowl! Aerial photo from Google Maps

Among the least-scenic of wetlands are those associated with mines. Iowa has many such wetlands, because Iowa has many abandoned mine sites.

Surprised? Most people are! Yet Iowa has been in the mining business since long before being a State, actually since before 1700. The “Mines of Spain” and associated lead smelter near Dubuque were economically & politically important (lead=ammunition=military might). Over the centuries, Iowa has also produced gypsum, zinc, sand, gravel, and especially coal. Iowa was the leading coal-producing state west of the Mississippi at the turn of the 20th century.

Both surface (strip and pit) and subsurface (shaft and slope) coal mining were employed, and although there’s no coal mining in Iowa anymore, the effects of coal mining are still clearly visible today in many locations. The southern counties of Marion, Mahaska and Monroe were especially productive, with mining continuing into the 1990s. In the vicinity of Albia we have a landscaped pockmarked with mine sites, some reclaimed and some simply abandoned. Here at Cottonwood Pits, several big rectangular basins are filled with water…and could perhaps float ducks; why not call it a “State Game Management Area?” And so it is.

In this part of the world, we have “well-buffered” soils, quite resistant to acidification. So old pits like these are usually not the deathly hollows common to coal mining in other parts of the country. These systems nevertheless, have unusual and variable chemistry. Prominent are metals, like oxides of iron, leached from the rock. So if surfaces in contact with the water often appear rusty…it’s because they are! In contact with oxygenated water, the dissolved iron oxidizes…and that may cause it to form a solid precipitate (I believe that’s the rusty glob seen floating in this photo and resting on my hand).


DSC_0068[1]So, how about that chemistry? Not bad, actually: perhaps in the decades since mining ended, conditions have stabilized? The sulfur (i.e., Sulfate) was low (only 9 mg/L). The pH was high (8.7), so no acidification problems here. The work of biota, weathering, and the well-buffered soils (high in carbonate) all help stabilize the system.

What about the animals? We observed a few fish, and a Great-Blue Heron (presumably eating fish). It appears turtles like this place…well enough to nest, at least (see photos below). These were a step away from the shoreline, in disturbed soil.

Let me close by pointing out that Iowa coal was formed on the sites of Carboniferous Period swamps, some 300 million years ago. In other words, the coal is a gift from ancient wetlands. Once again: wetlands at your service!

Author: Paul Weihe

Associate Professor of Biology at Central College, traditional author (Textbook of Limnology, Cole & Weihe, 5th ed.; Waveland Press), and now...blogger!

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