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3 THE WESTERN CORN BELT PLAINS The Western Corn Belt Plains is a region of rolling hills composed of thick deposits of loess over glacial till. Early explorers such as Lewis and Clark traveled up the Missouri River and left many descriptions of this area. It was once a tallgrass prairie of big and little bluestem, switchgrass and Indiangrass with oak-hickory woodlands along some of the streams like the Missouri River. Much of the region has been converted to cropland and, as a consequence, groundwater and surface water contamination by pesticides and fertilizer as well as runoff from feedlots is a significant issue. With the conversion from prairie to crops, streams are much more prone to flooding so many dams have been built causing extensive fragmentation of watersheds. The streams in this region have been extensively altered. Beginning in the early 1900's, many streams have were straightened in an effort to reduce flooding and to get more land into cultivation. The straightening of stream channels shortens them which increases the stream's gradient. A shorter, steeper stream has more power to erode its bed, especially during floods. As the stream bed erodes, the channel gets deeper (degrades) and the banks become unstable causing them to fail and fall into the channel. At the same time, the stream is trying to re-establish its original gradient by filling its lower end and eroding its headwaters (i.e. lengthening its channel). Those streams that were not directly straightened but are tributary to a straightened stream are also affected, because, as the main stream's channel cuts downward, the tributaries must follow. This bed degradation and erosion continues until a layer that is resistant to erosion (bedrock or hard clay layers). As a general rule, natural streams have a variety of habitats. Shallow gravel/cobble riffles, deep spools, moderate depth runs along with silty, vegetated oxbows or side channels. Now many, if not most, of the streams in this region have little diversity and minimal habitat for aquatic animals like crayfish. THE CENTRAL GREAT PLAINS The Central Great Plains ecoregion is a large section of south-central Nebraska and to discuss this we must break it into four subregions. North of the Platte River are the Dissected Loess Plains, a region of wind- deposited loess that can be over 200 feet thick. The land is hilly with moderate to steep slopes that have been eroded into canyons and deep valleys. Due to the irregular nature of the topography, it is primarily rangeland though increasing irrigation development is bringing more land into cropland. There are only a few perennial streams crossing this area which include the South, Middle and North Loup Rivers as well as Mud Creek, the Cedar River and Beaver Creek. In the east-central portion and south of the Platte River is the Rainwater Basin. This area is also overlain with a mantle of windborne loess which is a broad, flat area where you can see for miles in every direction. The photo below shows a portion of the Rainwater Basin west of Aurora, Nebraska. The Rainwater Basin has