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Ecoregions of
North Dakota
and
South Dakota

48. Lake Agassiz Plain


48a. Glacial Lake Agassiz Basin Level IV Ecoregion

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North Dakota Ecoregions

South Dakota Ecoregions

48a. Glacial Lake Agassiz Basin

48b. Sand Deltas and Beach Ridges

48c. Saline Area

  Glacial Lake Agassiz was the last in a series of proglacial lakes to fill the Red River Valley since the beginning of the Pleistocene. The Lake agassiz Plain is composed of thick lacustrine sediments underlain by glacial till. It is extrememly flat and has fewer lakes and pothole wetlands than neighboring ecoregions. The historic tallgrass prairie has been replaced by intensive agriculture. The preferred crops in the northern half of the region are potatoes, beans and wheat; soybeans and corn predominate in the south. Sugar beets are grown throughout the region.

GIF - Sprayer
The application of pesticides and fertilizers contributes to nonpoint source water pollution in the Glacial Lake Agassiz Basin (48a). Photo by South Dakota Tourism

From the Pembina Escarpment (46a), the view of the Glacial Lake Agassiz Basin is of an extremely flat patchwork of cultivated farmland. Because the Red River of the North has a poorly defined floodplain and very low gradient, flooding can be a problem. Outside of channelized areas in the floodplain, turbid valley streams meander within narrow buffer strips of cottonwood, elm, ash, and willow. Soils range from silty to clayey in texture. Most have high water tables and are extremely productive.

Physiography

Area (square miles): 5137

Elevation/Local Relief (feet): 790-1200/1-50

Extremely flat glacial lake plain. Streams and rivers sluggish, meandering, and highly turbid with large sediment loads. Ditching and channelization common.

Geology

Surficial Material and Bedrock
Thick beds of glacial drift, averaging 150-300 ft. overlain by up to 95 ft. of silt and clay lacustrine deposits from glacial Lake Agassiz. Bedrock geology: Cretaceous shales and sandstones, Ordovician and Precambrian basement rocks.

Soil

Order (Great Groups)
Mollisols (Calciaquolls, Endoaquolls, Haploborolls, Natriaquolls)

Common Soil Series
Bearden, Hegne, Glyndon, Ulen, Fargo, Gardena, Embden, Ryan

Temperature/Moisture Regimes
Frigid/Udic

Climate

Precipitation - Mean annual (inches)
18-21

Frost Free - Mean annual (days)
95-125

Mean Temp. - Jan. min/max; July min/max, (°F)
-7/12;56/82

Potential Natural Vegetation

Tallgrass prairie: big and little bluestem, switchgrass, and indiangrass. Cottonwood, willow, green ash, burr oak and American elm in riparian areas and on the Pembina Delta.

Land Use and Land Cover

Intensive row crop agriculture. Potatoes, edible beans, and wheat in the north; soybeans, corn, and wheat in the south. Farmland with woodlot or shelterbelt plantings. Urban and rural residential development.

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