Need for ecosystem management of large rivers and their floodplains Sparks, R. E. 1995. Need for ecosystem management of large rivers and their floodplains. BioScience 45(3):168 182. Reprinted by U.S. Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, April 1997. LTRMP 97-R004. 15 pp. (NTIS #PB97-166086) ABSTRACT Most of the 79 large river-floodplain ecosystems in the world have been altered by human activities. Nevertheless, these complex ecosystems still harbor a substantial portion of Earth's terrestrial and freshwater species and provide migration corridors and refuges within landscapes that have been developed for human use. The master variables that regulate physical, chemical, and biological processes in these ecosystems are the water and sediment regimes. The goal of ecosystem management should be to maintain or recover the biological integrity of the ecosystem, where integrity includes both the biological communities that were typical of the natural habitat of the region and the processes required to sustain them. The reference condition for ecosystem management can be identified from historical data or from relatively undisturbed reaches or rivers, or inferred by application of general ecological principles and known cause-effect relationships. Despite a century of alteration in the Illinois and Upper Mississippi Rivers, flood pulses still occur on approximately half the original floodplain area where there are no levees, and these rivers are good candidates for the application of ecosystem management. The navigation dams on these rivers do not stop floods and are designed to allow sediment in the channels to pass through the dams. The dams do alter the temporal-spatial pattern of flooding over about a fourth of the length of the rivers, but dam operations could be modified to recreate a more natural flooding pattern. Portions of the rivers have been altered by increases in the sediment load and changes in the water regime resulting from intensive land use in the drainage basin. There are more rapid and frequent water level fluctuations and the floodplains have been permanently inundated immediately upstream of the navigation dams. Filling of these inundated areas with sediment is widely regarded as a major problem, but from a long-term, geological perspective, the rivers are simply building themselves new floodplains. The new sedimentary equilibrium that is likely to be reached by 2050 may look like the predisturbance floodplain, but at a higher elevation. A less desirable scenario is that the new floodplain in the vicinity of the dams will lack topographic relief and therefore have less habitat diversity. The combined predictive expertise of fluvial geomorphologists and ecosystem ecologists, in concert with operational and structural changes in the human-dominated portions of the watersheds and river channels, will be needed to institute ecosystem management and recover ecosystem integrity. Ecosystem management is likely to save money and increase economic efficiency in the long run, because natural services and processes are restored (e.g., flood storage, conveyance, and moderation; water purification; production of fish and wildlife; and preservation of biodiversity) instead of being largely replaced by human intervention at greater cost and risk of failure. The implementation cost and degree of success in the long term depend heavily upon understanding ongoing geological and biological processes and taking actions now that capitalize on the long-term trends. KEYWORDS Backwater, basin, biodiversity, biological integrity, channel, conservation, ecological health, ecological integrity, ecosystem management, flood, floodplain, floodpulse, habitat diversity, Illinois River, invasive species, landform, landscape, levee, Mississippi River, navigation dam, restoration, sediment, water regime, watershed, wetland