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Wetland Resources of Eastern South Dakota

Executive Summary

Eastern South Dakota, comprised of 44 counties east and north of the Missouri River, covers about 35,400 square miles. Wetlands and deepwater habitats account for 2,222,113 ac (899,277 ha) or 9.8% of the landscape. Of this total, palustrine system wetlands constitute 80.1% (1,780,859 ac or 720,704 ha), lacustrine system wetlands and deepwater habitats 16.8% (371,982 ac or 150,538 ha), and riverine system wetlands 3.1% (69,273 ac or 28,034 ha).

A total 932,829 wetland basins (potholes or lakes, for example) covering 2,128,674 ac (861,463 ha) delineated from palustrine and lacustrine wetlands occur in eastern South Dakota. Temporary basins make up 55.7% (520,379) of the total number of basins and 18.3% (390,054 ac or 157,853 ha) of the total area. Seasonal basins make up 35.9% (334,699) of the total basins and 26.0% (553,515 ac or 224,004 ha) of the total area. Semipermanent basins make up 8.1% (76,260) of the total basins and 34.0% (722,904 ac or 292,555 ha) of the total area. Permanent basins (basins containing lacustrine wetlands or permanent or intermittently exposed palustrine wetlands) comprise 0.2% (1,457) of the total number of basins and 21.7% (462,201 ac or 187,050 ha) of the total area. Of all semipermanent basins, 23,997 are natural basins -- that is, they contain at least one semipermanent wetland -- covering about 377,660 ac (152,837 ha); 38,663 covering 237,069 ac (95,941 ha) are shallower basins with dugouts or other excavations or are isolated dugouts; and 11,527 covering 99,411 ac (40,231 ha) are impoundments. A total 603 natural permanent basins occur in eastern South Dakota covering 194,037 ac (78,526 ha). A total 384 permanent basins are impoundments, comprising 264,156 ac (106,902 ha), mostly in the Missouri River reservoirs.

The median size of basins in eastern South Dakota is only 0.4 ac (0.16 ha). Of all eastern South Dakota basins, 58.8% are ≤0.5 ac (0.2 ha) in size; 72.9% are ≤1.0 ac (0.4 ha); 83.4% are ≤2.0 ac (0.8 ha); and 92.1% are ≤5.0 ac (2.0 ha). Only 2.6% are larger than 10 ac (4.0 ha).

Eastern South Dakota has a recent history of glaciation; consequently, drainage networks of riverine wetlands are poorly developed over most of the region. The best developed drainage networks occur on the western slope of the Missouri Coteau and east of the Big Sioux River, areas that were not covered by Late Wisconsin glaciers.

Over most of eastern South Dakota, water travels by surficial flow into insular basins that formed from melting ice blocks deposited in glacial till. The distribution and characteristics of basins in eastern South Dakota were influenced by the timing, frequency, and manner of glaciation. Low relief landscapes, such as ground moraine or glacial lake plains, tend to include numerous shallow temporary and seasonal basins, while high relief landscapes, such as terminal or dead-ice moraine, tend to include deep basins with semipermanent or permanent water regimes.

Temporary and seasonal basins are most abundant in the James River Lowland and Minnesota-Red River Lowland physiographic regions, the paths along which glaciers advanced. Natural semipermanent and permanent basins are most abundant on the Prairie Coteau physiographic region.

Most basins at the northern end and along the eastern margin of the Prairie Coteau are small. In the interior of the Coteau, semipermanent and permanent basins occur in more gradually undulating terrain and are larger. Chains of permanent lakes occur adjacent to the west side of the Big Sioux River within the Prairie Coteau. Most of these lakes formed like smaller basins, but the ice mass in this area was subject to less compression and was less fragmented. Basins with semipermanent water regimes due to excavated dugouts are widely distributed across eastern South Dakota, but semipermanent and permanent impoundments are most abundant on the western slope of the Missouri Coteau.

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