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General Characteristics. Although much of central United States and Canada is characteristically prairie, the streams of a large part of this region could not, with any justification, be spoken of as " prairie streams," since their immediate environment is often heavily wooded. Thus the uplands of Illinois and Indiana are typically prairie, but the valleys through which their streams flow were originally deciduous forest and savannah. The same is true of Missouri and Iowa. As woodlands tend to follow up water courses, it is not until after one has crossed the Missouri River and the eastern part of Kansas and Nebraska, or has gone north into the Dakotas, that one really encounters prairie streams and ponds. Thus the " aquatic biology of the prairie " is far more restricted geographically than the prairie. Figures 2 and 3, showing Deep Creek of northeastern Kansas, and Peace Creek of central Kansas illustrate the difference between the savannah and prairie streams. The former, flowing between wooded banks, receives shade during the summer and a blanket of dead leaves each fall, which in decomposing, add to the organic ooze or humus of the bottom. This provides food and shelter for a large number of worms, molluscs, insect larvae and other benthic forms, while numerous logs, fallen trees, and masses of roots support their characteristic faunas, rendering the bottom the most productive part of the stream. The prairie stream, on the other hand, receives very little organic matter from the shore. In analyzing mud samples from the bottom of the Big Muddy and Sangamon Rivers in Illinois the author has found as much as 50 to 8o per cent of the dry weight to be organic in nature, while dredgings from the bottom of several prairie streams have shown only gravel, sand, or clay, practically free of organic content. The streams of Eastern Kansas (Fig. 2), form a transition between the typical woodland streams of ' Delivered before the Ecological Society of America in the Symposium on " Prairie Ecology," Kansas City, Mo., December 30, 1925. Contribution No. 95 of the Department of Zoology, Kansas State Agricultural College. 2 The author is indebted to her graduate students, Elmer P. Cheatum, Harry G. Walker, and Frank W. Jobes, who took part in most of the field trips. 289 |
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