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Historical alterations of surface hydrology in Iowa's agricultural watersheds.
Andersen, Katherine1, Menzel, Bruce1, 1
ABSTRACT- Iowa's headwater prairie streams exist in direct contact with an agricultural matrix. This study determined historic changes in surface water features of four small agricultural watersheds. Bear Creek watershed was once part of the "wet prairie" region within the Des Moines Lobe landform of north-central Iowa. Storm Lake watershed, located in the Northwest Iowa Loess Prairies landform, was of a similar original condition with limited stream channel development. The Walnut Creek and Three Mile Creek watersheds are located in the Southern Iowa Rolling Loess Prairies landform, a more erosionally-mature region. Historical information about natural surface hydrology features of the four watersheds were obtained from General Land Office survey records of the mid-1800's, original drainage districts maps from the early 1900's, county atlases and other historical sources. These data were integrated into a GIS and compared with modern features depicted on USGS topographical maps. Study results for the northern watersheds showed that nearly all the original wetland features have been eliminated since settlement and replaced by streams largely of artificial origin. This acceleration of stream development includes dramatic increases in channel lengths and incision. In contrast, the southern watersheds have had many natural stream segments altered or eliminated by impoundments and channelization. These findings help to establish "reference conditions" of prairie hydrologic features and document historical effects of agricultural activity.
KEY WORDS: stream ecology, restoration , riparian, wet prairie