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<br /> <br />CHAPTER 3: MODlPICA nONS OF UPPER MISSISSIPPI RIVER AND EFFECTS ON FLOODPLAIN FORESTS 31 <br /> <br /> <br />-;; ~ A Presettlement Floodplain .~ 0 <br />~ .0 ~1ii <br />.e .~ Mississippi river mile 218 a: o.~ <br /><! 0. 1i ~.e <br />u 0. <br />= ... i ~ "' = 0 .~ Ii: <br />Q. = ~ ~ ~1ii <br />::> '" ~ .~ .~ <br /> ~ 0. o.~ <br /> 0 ~ .Ii '" ~.o " <br /> & .0 <br /> 1'! 0 <br /> 0 jj ~ <br /> <i a. '" <br /> ~ <n <br /> c <br /> . ., I,!!I' <br /> :,!.~..,. .> <br /> <br /> <br />Missouri <br />Bluff <br /> <br />~ Ridge $wale <br />Aoodplain (distance 4-7 miles) <br /> <br />-;; <br />~ <br />.e <br />" <br />o <br />= <br />Q. <br />::> <br /> <br />e <br />~ <br />= <br />~ <br />u <br />.0 <br />~ <br /><( <br /> <br />Area of detail <br />in figure 3-5 A <br />I <br /> <br />Illinois <br />Bluff <br /> <br />e <br />~ <br />= <br />~ <br />u <br />.0 <br />~ <br /><( <br /> <br />o <br />Oi_ <br />o..~ <br />~.e <br />u. <br /> <br /> <br />~ <br />if <br />.5. <br />0. <br />.. <br />. <br />.~ <br />" <br /> <br />o <br />'iij- <br />15..:g <br />~.o <br />Ii: <br /> <br />-;; <br />~ <br />.e <br /><! <br />= <br />Q. <br />::> <br /> <br />B <br /> <br />Present Floodplain <br />Mississippi river mile 218 <br /> <br />~ <br />J <br />o <br />~ <br /><i <br />~ <br />~ <br />C <br /> <br /> <br /> <br />Area of detail <br />inrl ura3-58 <br />I <br /> <br />Illinois <br />Bluff <br /> <br />Missouri <br />Bluff <br /> <br />Oxbow R.dg S al Agricultural <br />lake I ewe levee <br />Floodplain (distance _ 4-7 miles) <br /> <br />Figure 3-2. Cross-section diagrams of the Mississippi floodplain at river mile 218 of an impounded reach. A, In the presettlement era, <br />the floodplain was dominated by prairie wetlands. B, Presently, agriculture has replaced the prairies, but many of the floodplain forests <br />still remain, although they are less diverse in structure and species. <br /> <br />ReI <br /> <br />~ 1)'picallimilsofrivercategory <br /> <br />~unl Bluff <br />I I <br />I I <br />Bluff I I Bluff <br />"""l\ F"'*"a" r <br />I~i <br /> <br />RC2 <br /> <br /> <br />8''''' <br />I <br />I <br />I <br />, <br /> <br />Ta"""" <br /> <br />AoodplaJo <br /> <br />RC3 <br /> <br />F\oodpIIIif'l <br /> <br />TemlC6 Floodplain <br /> <br />8''''' <br />I <br />I <br />I <br /> <br />RC4 <br /> <br />Figure 3-3. Four common river categories (Res) in the upper <br />Mississippi River (source: Upper Mississippi River Basin <br />Commission, 1982). <br /> <br />In the spring the Mississippi River normally over- <br />flowed and temporarily inundated the lowest lying flood- <br />plain habitats. These floodplain habitats, termed aquatic <br />terrestrial transition zones (ATTZs) (Junk and others, 1989), <br />alternated between aquatic and terrestrial conditions. <br />ATTZs were often made up of diverse woodlands of various <br />size structures and age classes and (or) prairie wetlands. <br />Plant species were well adapted to periodic flooding, and, <br />during the spring aquatic phase, provided river fishes with <br />an abundant food supply, spawning and nursery habitats, <br />and shelter from predators. In turn, the river deposited nutri- <br />ent-rich sediments on the floodplain, which plants utilized <br />throughout the summer growing season after spring flood- <br />waters receded. Annual flooding in the autumn months <br />could follow low-flow periods during the summer growing <br />season. The autumn flood was either a separate event or a <br />prelude to spring flooding. During this time of year, plants <br />be~an senescence. and rising river water levels again <br />flooded some ATTZs. It was in these transition zones that <br />