The Prairie Pothole Region (PPR; french: Région des cuvettes/fondrières des prairies) is an expansive area of the northern

Great Plains The Great Plains (french: Grandes Plaines), sometimes simply "the Plains", is a broad expanse of flatland in North America. It is located west of the Mississippi River and east of the Rocky Mountains, much of it covered in prairie, steppe, a ...

that contains thousands of shallow

wetland A wetland is a distinct ecosystem that is flooded or saturated by water, either permanently (for years or decades) or seasonally (for weeks or months). Flooding results in oxygen-free (Anoxic waters, anoxic) processes prevailing, especially in t ...

s known as potholes. These potholes are the result of

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such a ...

activity in the

Wisconsin glaciation The Wisconsin Glacial Episode, also called the Wisconsin glaciation, was the most recent glacial period of the North American ice sheet complex. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cord ...

, which ended about 10,000 years ago. The decaying ice sheet left behind depressions formed by the uneven deposition of

till image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...

in ground moraines. These depressions are called potholes, glacial potholes, kettles, or kettle lakes. They fill with water in the

spring Spring(s) may refer to: Common uses * Spring (season), a season of the year * Spring (device), a mechanical device that stores energy * Spring (hydrology), a natural source of water * Spring (mathematics), a geometric surface in the shape of a h ...

, creating wetlands, which range in duration from temporary to semi-permanent. The region covers an area of about 800,000 sq. km and expands across three Canadian provinces (

Saskatchewan Saskatchewan ( ; ) is a Provinces and territories of Canada, province in Western Canada, western Canada, bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and on t ...

Manitoba Manitoba ( ) is a Provinces and territories of Canada, province of Canada at the Centre of Canada, longitudinal centre of the country. It is Canada's Population of Canada by province and territory, fifth-most populous province, with a population o ...

, and

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest T ...

) and five U.S. states (

Minnesota Minnesota () is a state in the upper midwestern region of the United States. It is the 12th largest U.S. state in area and the 22nd most populous, with over 5.75 million residents. Minnesota is home to western prairies, now given over t ...

Iowa Iowa () is a U.S. state, state in the Midwestern United States, Midwestern region of the United States, bordered by the Mississippi River to the east and the Missouri River and Big Sioux River to the west. It is bordered by six states: Wiscon ...

North North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. ''North'' is a noun, adjective, or adverb indicating direction or geography. Etymology The word ''north ...

and

South Dakota South Dakota (; Sioux: , ) is a U.S. state in the North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Lakota and Dakota Sioux Native American tribes, who comprise a large po ...

, and

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columb ...

). The hydrology of the wetlands is variable, which results in long term productivity and biodiversity. The PPR is a prime spot during breeding and nesting season for millions of migrating waterfowl.

Hydrology

Few natural

surface water Surface water is water located on top of land forming terrestrial (inland) waterbodies, and may also be referred to as ''blue water'', opposed to the seawater and waterbodies like the ocean. The vast majority of surface water is produced by pre ...

drainage systems occur in the region as pothole wetlands are not connected by surface streams. They receive most of their water from spring

snowmelt In hydrology, snowmelt is surface runoff produced from melting snow. It can also be used to describe the period or season during which such runoff is produced. Water produced by snowmelt is an important part of the annual water cycle in many p ...

and precipitation. Some pothole wetlands also receive

groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...

inflow, so they typically last longer each year than those that only receive water from precipitation. Shorter-duration wetlands fed only by precipitation typically are sources of

groundwater recharge Groundwater recharge or deep drainage or deep percolation is a hydrologic process, where water moves downward from surface water to groundwater. Recharge is the primary method through which water enters an aquifer. This process usually occurs ...

. The hydrology of the potholes is very variable, responding to changes in precipitation and groundwater, and results in regular wet-and-dry cycles.

Vegetation

The vegetation of the PPR consists of emergent plants and tall grasses, while the prairie surrounding the region has dense grassland vegetation. The composition of a local plant community is heavily affected by the amount of water available. In wetter wetlands that retain water through the summer, the common plant is hard-stem bulrush, along with soft-stem bulrush and common threesquare in slightly drier regions of the wetlands. The vegetation in permanently flooded wetlands is more aquatic;

duckweeds Lemnoideae is a subfamily of flowering aquatic plants, known as duckweeds, water lentils, or water lenses. They float on or just beneath the surface of still or slow-moving bodies of fresh water and wetlands. Also known as bayroot, they arose f ...

, pondweeds, aquatic buttercups, and aquatic

smartweeds ''Polygonum'' is a genus of about 130 species of flowering plant in the buckwheat and knotweed family Polygonaceae. Common names include knotweed and knotgrass (though the common names may refer more broadly to plants from Polygonaceae). In the ...

are some of the most common. In drier wetlands of the PPR, the vegetation varies from

spikerush ''Eleocharis'' is a virtually cosmopolitan genus of 250 or more species of flowering plants in the sedge family, Cyperaceae. The name is derived from the Greek words ἕλειος (''heleios''), meaning "marsh dweller," and χάρις (''charis' ...

, which is found in the wetter areas of the wetland, to foxtail barley and wheatgrass on the outer edges of the wetland. The variable availability of water in the Prairie Pothole Region is buffered by an abundant seed bank under the soil, comprising species that thrive under different water regimes. During times of drought, shortgrass species increase and expand their range, while during wetter periods, tallgrass and mixed prairie communities become more common.

Wildlife

The Prairie Pothole Region provides important habitats for migratory waterfowl and other wildlife, supporting more than 50% of

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and th ...

's migratory waterfowl. In particular, the region is one of North America's most important breeding areas for

duck Duck is the common name for numerous species of waterfowl in the family Anatidae. Ducks are generally smaller and shorter-necked than swans and geese, which are members of the same family. Divided among several subfamilies, they are a form ...

s. Although the region contains only about one-tenth of the continent's habitat area for breeding of waterfowl, roughly half the primary species of game ducks on the continent breed there. The region accounts for more than 60% of the breeding populations of

mallard The mallard () or wild duck (''Anas platyrhynchos'') is a dabbling duck that breeds throughout the temperate and subtropical Americas, Eurasia, and North Africa, and has been introduced to New Zealand, Australia, Peru, Brazil, Uruguay, Argen ...

gadwall The gadwall (''Mareca strepera'') is a common and widespread dabbling duck in the family Anatidae. Taxonomy The gadwall was first described by Carl Linnaeus in his landmark 1758 10th edition of ''Systema Naturae''. DNA studies have shown that ...

blue-winged teal The blue-winged teal (''Spatula discors'') is a species of bird in the duck, goose, and swan family Anatidae. One of the smaller members of the dabbling duck group, it occurs in North America, where it breeds from southern Alaska to Nova Scoti ...

northern shoveler The northern shoveler (; ''Spatula clypeata''), known simply in Britain as the shoveler, is a common and widespread duck. It breeds in northern areas of Europe and across the Palearctic and across most of North America, wintering in southern ...

northern pintail The pintail or northern pintail (''Anas acuta'') is a duck species with wide geographic distribution that breeds in the northern areas of Europe and across the Palearctic and North America. It is migratory and winters south of its breeding ...

, redhead, and

canvasback The canvasback (''Aythya valisineria'') is a species of diving duck, the largest found in North America. Taxonomy Scottish-American naturalist Alexander Wilson described the canvasback in 1814. The genus name is derived from Greek ''aithuia'', ...

ducks.

Threats

Conversion of land for

agriculture Agriculture or farming is the practice of cultivating plants and livestock. Agriculture was the key development in the rise of sedentary human civilization, whereby farming of domesticated species created food surpluses that enabled people ...

is a significant factor in the loss of wetlands in the PPR. More than half of the wetlands have been drained for farming. In particular, 90% of the prairie wetlands of the

Minnesota River The Minnesota River ( dak, Mnísota Wakpá) is a tributary of the Mississippi River, approximately 332 miles (534 km) long, in the U.S. state of Minnesota. It drains a watershed of in Minnesota and about in South Dakota and Iowa. It ris ...

basin have been lost as habitat. The wetlands that do persist, surrounded as they are by agricultural lands, are also affected. Chemical runoff, sedimentation, and nutrient flow into the wetlands have adverse impacts.

Climate change In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

is an adverse factor in the long-term viability of PPR wetlands for breeding ducks and other birds. Without mitigation, severe droughts and rising temperatures will cause many pothole wetlands to dry up sooner in the spring. In turn, due to the timing of waterfowl migrations, these dried wetlands will not present suitable breeding habitat. Warming-related drought may affect as much as 90 percent of the PPR's remaining wetlands. Simulations suggest that climate change will shift the most productive wetlands from the center of the region (southeastern Saskatchewan and the Dakotas) to edges of the PPR in the east and north. However, research has suggested that the effect of global warming is overshadowed by that of intensified land use and drainage of wetlands.

References

External links

* * *
America’s Grasslands: A Threatened National Treasure
Documentary produced by Prairie Public Television
Land-use Change, Economics, and Rural Well-being in the Prairie Pothole Region of the United States

United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...