Water goes. That is one of the few givens in hydrology – water is going to go somewhere, always down hill, or down into the soil. Which raises interesting questions for those living at the bottom of hills or in flat places. In many parts of the world, flat places tend to be soggy places. The Great Plain of Hungary was an enormous wetland prior to the 19th century and drainage plans. Large swaths of Germany also contained marshes and moors, in some ways like the Fens in England or what are now the drained lands of Holland (aka the Low Countries.) The same held true for central North America. The Dakotas, Manitoba, Saskatchewan, parts of Minnesota and Iowa, and the High Plains of Texas contained multiple natural lakes. But they were very different, with different origins and life-cycles.From above, the pothole prairies and the playas of the High Plains all shimmer in the sun. All are mostly round and surrounded by grass and forbs (wildflowers and woody plants). On the ground the differences become more apparent. The Pothole Prairies are more rolling, although not dramatically so. And the soil is black, rich from the thousands of years of tall-grass roots and decay. The potholes date to the end of the last ice age, when the Canadian ice sheets retreated and left a lumpy, undrained, young landscape. The playas go back a few thousand years before that and owe their existence to groundwater nibbling from below as much as to erosion from above.
Pothole prairies form one of the most important flood control features of the Northern Plains. They catch snowmelt that would otherwise run across the landscape and into the Red River of the North, the James River, the upper Missouri, and other streams. By slowing the flow, they allow a more gradual rise and fall, and keep the ground moist longer. The Dakotas have a Continental climate, meaning they go from very, very cold to very, very hot. All that moisture helps buffer things a little, and the potholes ease the speed of the melt.
The potholes also keep duck hunters and other water fowl enthusiasts busy. Ducks and geese and other birds make use of the potholes for nesting. They hide their nests in the tall grasses, and eat the different plants and small animals and insects that live in and around the lakes. Waterfowl also make use of the playa lakes, but in winter rather than in summer (most of the time). The great migratory routes across North America include the pothole prairies and the playas, thousands of small refuges amidst the increasing development in the river valleys and uplands.
In part because of that rich, rock-free soil, pothole prairies are an endangered environment. Until the 1880s, farmers avoided the area because it was too wet to plow, too boggy, and too dangerous in winter. Those readers who are familiar with Laura Ingalls Wilder’s The Long Winter may recall the dangers of falling into the “sloughs,” low, boggy areas hidden by the snow that caused sled wrecks and horse injuries when people stumbled into them. The sloughs are another name for pothole wetlands. It was not until the development of tiling and bull-ditches that breaking the rich lands of the pothole prairies became possible. Farmers dug trenches and lined them with perforated tiles, forming large drainage paths that led into streams. Deep ditches also helped speed water away from the land, and plowing up the potholes, knocking the ridges of soil into the low spots, accelerated the process. Millions of potholes became part of the wheat-basket of North America.
The first attempts to preserve the potholes came from hunters. Ducks Unlimited and the Isaac Walton League were early conservation proponents who recognized that the prairies grew waterfowl as well as wheat. The Audubon Society and others followed, and by the early 20th Century, a few pockets had been preserved. Although not as numerous or varied as they once were, bits of pothole prairie survive. The great floods of the Red River of the North and the Upper Mississippi in the 1990s served as another reminder that wetlands play a critical role in regulating the hydrology of a very flat landscape.