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Wetland Resources of Eastern South Dakota

Results and Discussion

Riverine Wetlands

System, Subsystems, and Classes
Drainage networks of riverine wetlands have developed slowly in South Dakota's subhumid and semiarid environments and are most abundant in counties in the northern James River Lowland and in southeastern South Dakota bordering free-flowing reaches of the Missouri River (Fig. 16). Wetlands in the riverine system cover 69,273 ac (28,034 ha) of eastern South Dakota (Table 2). Of the total area, 50,576 ac (20,468 ha) or 73% are comprised of riverine wetlands wide enough to be delineated with polygons, and 18,695 ac (7,566 ha) or 27% are comprised of linear wetlands (using a 48 ft-wide [14.64 m] buffer for linear wetlands for area calculation).

GIF - Distribution of Riverine Wetlands
Figure 16. Distribution of riverine wetlands in eastern South Dakota. Discontinuities in river channels indicate impoundments or intervening stretches of palustrine wetland.

The eight counties with the most riverine wetland habitat, ranked from most to least, were Spink (5,710 ac or 2,311 ha), Brown (4,539 ac or 1,837 ha), Yankton (3,949 ac or 1,597 ha), Clay (3,912 ac or 1,583 ha), Union (3,697 ac or 1,496 ha), Charles Mix (4,033 ac or 1,632 ha), Bon Homme (3,526 ac or 1,427 ha), and Beadle (3,170 ac or 1,283 ha) (Appendix B).

Riverine wetlands in the lower perennial subsystem (for example, the Missouri, James, or lower Big Sioux rivers) cover 35,257 ac (14,269 ha) or 50.9% of total riverine wetland area. The unconsolidated bottom class of lower perennial riverine wetlands covers 32,034 ac (12,964 ha) or 90.7% of lower perennial riverine habitat, while wetlands in the unconsolidated shoreline class, or mud and sandbars, cover 3,225 ac (1,305 ha) or 9.1% of total lower perennial riverine habitat.

One reach of upper perennial riverine habitat occurs in eastern South Dakota at the falls of the Big Sioux River in the city of Sioux Falls. This area covers approximately 7 ac (2.7 ha) and is in the unconsolidated bottom class.

Riverine wetlands in the intermittent subsystem cover 34,016 ac (13,766 ha) or 49.1% of total riverine wetland area. Intermittent riverine wetlands were always classified by the NWI in the streambed class (with rocky or muddy substrates) and often alternate along the course of a stream with palustrine emergent wetlands.

Water Regimes
Semipermanent riverine habitat in eastern South Dakota, like the Big Sioux north of Brookings, covers 30,611 ac (12,388 ha) or 44.2% of the total area of riverine habitat. The next most abundant riverine wetland water regime is permanent, which covers 19,281 ac (7,803 ha) or 27.8% of the total area. Riverine wetlands with the intermittently exposed water regime cover 12,133 ac (4,910 ha) or 17.5% of the total area. Seasonal riverine wetlands cover 3,981 ac (1,611 ha) or 5.7% of the total area; and temporary riverine wetlands cover 3,267 ac (1,322 ha) or 4.7% of the total riverine habitat in eastern South Dakota (Fig. 17).

GIF - Percentage of Riverine Wetlands by Water Regime
Figure 17. Percent of total acres of eastern South Dakota riverine wetlands by water regime.

Special Modifiers
Excavation has created or modified 2,166 ac (876 ha) or 3.1% of riverine habitat in eastern South Dakota. The other 67,107 ac (27,158 ha) or 96.9% of riverine habitat that remain in eastern South Dakota have not been directly altered by excavation.

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