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Wetland Resources of Eastern South Dakota

Results and Discussion

Seasonal Basins

The 334,699 seasonal basins that cover 553,515 ac (224,004 ha) comprise from 0.9% to 5.6% of the area of eastern South Dakota counties (Table 8). Seasonal basins occur at high relative densities in scattered regions throughout eastern South Dakota (Figs 32, 33). Small seasonal basins are abundant on end moraine in the James River Lowland. Large seasonal basins also are common in this region and occur in the low areas between recessional moraines.

Seasonal basins also are abundant on the Altamount Moraine (the lateral moraine of the Des Moines lobe of Late Wisconsin glaciers) and on the northeastern Missouri Coteau. Seasonal basins in these areas formed from the melting of ice blocks imbedded in till deposited by stagnant, wasting glaciers. Many basins on the northeastern Missouri Coteau have shallow depth profiles, probably because the amount of till deposited here was relatively small during Late Wisconsin glaciation. The coteau escarpment rises gradually in this area, and the ice/debris mass was thinner near its margin than farther east. Shallow depth profiles and a low regional precipitation:evaporation ratio produce seasonal water regimes in many basins in this area. Seasonal basins have a relatively low abundance over most of the Prairie Coteau, on the Lake Dakota Plain, and on the western half of the Missouri Coteau.

JPG - Distribution of Seasonal Basins
JPG - Distribution of Seasonal Basins
Figure 32. Distribution of seasonal basins expressed as number of basins/10 mi2. Figure 33. Distribution of seasonal basins expressed as acres of basins/10 mi2.

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