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CHAPTER 5: RESTORING AQUA TIC RESOURCES TO THE LOWER MISSOURI RIVER _ Stage - Temperature Use by tish ~. - , & I \ ~ h5 / \ ~ - . >- Jan. Dec. ~. r 5 . . N' J 8- (f.I \..... E - . >- Jan. Dec. A StagelTemperature eoupled B StagelTemperature Decoupled Figure 5-2. Hypothetical examples of river stage and tempera. ture relations for a large temperate river floodplain. A. Extended spring flood that. in combination with a nonnal temperature regime, provides good conditions for fish using floodplain habi- tats. B. Short-duration. early flood that is decoupled from tem- perature. This restricts productivity of fish and invertebrates in the floodplain but pennits greater productivity of macrophytes (sources: Junk and others. 1989: Sparks and others, 1990). gradually increasing water levels accompanied by a high- amplitude flood of long duration. Ideal conditions for spring spawners in temperate rivers occur during years in which the flood and water temperature rise are coupled (Junk and others, 1989), Alterations that decouple temperature from river stage restrict invertebrate and fish productivity in the floodplain (fig. 5-2) (Sparks and olhers, 1990). These ideas that rivers and their floodplains are so intimately linked thai they should be understood, managed, and restored as inte- gral parts of a single system make up the foremost integra- tive concept of restoralion efforts (National Research Council, 1992). NATURAL AND ANTHROPOGENIC DISTURBANCE Disturbance in latic waters has been defined as any unpredictable, discrete event that disrupts structure or func- tion at the ecosystem, community, or population level (Resh and others, 1988). Lack of predictability is an important componenl of this definition. Resh and others (1988) con- sider disturbances as events characterized by a frequency (rate of occurrence of events) and intensity (physical force of event per time) that are outside a predictable range (see Poff (1992) for an alternative perspective). Periodic flood pulses of large rivers are predictable events under this defi- nition. Indeed, the periodic naod pulse is critical to mainte- nance of aquatic populations, communities, and ecosystem processes. From this perspective. floods are not distur- bances, unless so amplified, reduced, or mistimed Ihat they fall oulside the long-term pattern (Sparks and others, 1990). Large floods are not disruptive events in the long term. as Ihey contribute to the dynamic equilibrium of the system. Such flood events can reset late successional stages to ear- 51 lier stages, thereby increasing habitat and species diversity (Sparks and olhers, 1990). Sand islands are an example of such an ephemeral early successional habitat in the Mis- souri River. Grace (1985) reported that 46 species, or two- thirds of the total fish fauna of the lower Missouri River. utilized this habitat. Also, Iwo federally listed birds, the least tern (Sterna antillarum) and piping plover (Charadrius melodus), nest primarily on sand islands. Humans have isolated rivers from their floodplains by draining and filling wetlands, channelizing river segments, constructing levees to contain flood flows within the main channel, and constructing mainstream dams and impound- ments to reduce downstream flooding and regulate flow (petts, 1984; Brookes, 1988; Ward and Stanford, 1 n89; Bayley, 1991). These activities have drastically affected aquatic communities and processes and severed the river- floodplain linkage. Channelization and damming, togelher with agricultural, municipal, and industrial pollution. con- stitute the major human-induced disturbances to the integ- rily of the world's large river ecosyslems. We will briefly describe the nominal state of the Missouri River and then summarize effects of these disturbances. MISSOURI RIVER ECOSYSTEM The Missouri River's present southeasterly diagonal course across the midcontinent of the United States traces the southern limils of Pleistocene glaciation (fig. 5-3). It is the longest river in Ihe United States, 3,768 kilometers, with a drainage basin encompassing about 1,327,000 square kilo- meters (km2) or about one-sixth of the continental United States. Four physiographic provinces make up its drainage basin: 142,000 km2 of the Rocky Mountains in the West, 932,000 km2 of the Great Plains in the cenler of the basin. 228,000 km2 of central lowlands in the north lower basin, and 24,500 km2 of the interior highlands in the south lower basin (Slizeski and others, 1982; Robison, 1986). River slope varies from about 38 meters per kilometer in the Rocky Mountains to an average of 0.17 meters per kilome- ter in the Great Plains and central lowlands (U.S. Army Corps of Engineers (USACE), 1985). A prominent feature of the Missouri River's drainage pattern is that most major lributaries in the upper and middle portions of the basin enter on the right bank, flowing to the east or northeast. Climale of the basin is controlled by three air circula- tion patterns: one originating in the Gulf of Mexico, another in the northern Pacific Ocean, and Ihe third in the northern polar region (US ACE, 1985). The freeze-free season ranges from fewer Ihan 40 days in the Rocky Mountains to more than 120 days in Ihe interior highlands (Hesse and others, 1989a). The drainage basin is generally arid and subject to seasonal and long-term droughts due to the dominance of the Great Plains physiographic region. Average annual pre- cipitation ranges from more than 80 centimeters in the