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Figure 16-22. View over TNC marsh toward the northeast showing extensive cattail thickets (dark gray). May 2011;
kite aerial photo by S.W. Aber and J.S. Aber.
Figure 16-23. Nebraska Sand Hills showing lakes (black), rivers, and drainage features. National wildlife refuges
are indicated by gray shading. Adapted from Keech and Bentall (1978, Fig. 2).
transition in available water gives rise to different
wetland zones (see Fig. 16-23). In the central and
eastern portions, perennial streams display
remarkably constant discharge fed by ground-
water basel ow; these streams rarely l ood or dry
up. In addition, sand hills streams have slightly
alkaline pH (7.7-8.1), low content of dissolved
solids (100-200 ppm), and low hardness (Bentall
1990). To the north and west, countless shallow
lakes occupy enclosed basins, as at Valentine
National Wildlife Refuge. Most of these are
slightly alkaline, fresh-water lakes associated
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