8150 - Laserfiche WebLink

Home Browse Search

236 C. H. THEILlNG Sparks et al., 1990; Bayley, 1991, 1995); (2) channel maintenance (i.e. dredging) costs and barge groundings are increased during drought periods; (3) drawdowns used to promote wetland plant production in wildlife management areas can be conducted on a system-wide scale using navigation dams; and (4) drawdown benefits will persist after a return to normal navigation system operation. I believe it represents a system approach that provides greater ecological benefits than present habitat rehabilitation or channel main- tenance efforts. This proposal is a better approximation of true restoration because it restores some of the ecological integrity of the Upper Mississippi River by restoring low river stages (abiotic control) experienced before navigation improvements. Its implementation would be a true test of 'ecosystem management' on the Upper Mississippi River (Sparks, 1995). It is proposed that system-wide drawdowns to natural base flow coincide with drought periods; they might be defined as 6-8 week periods during July and August of a 1 O-year drought, for example. Orawdowns would be achieved by simply opening the dam gates for a predetermined time period. Expected benefits include: (1) oxidization and consolidation of backwater and channel border sediments when exposed (Mitsch and Gosselink, 1986); (2) plant production on mud flats that will be recycled in the aquatic system when flooded again (Junk et al., 1989); (3) sediment stabilization by plant roots (Sparks et ai., 1990; Sparks, 1992); (4) sediment compaction when exposed and dried; and (5) increased sediment transport in the main channel due to increased current velocities. Improved backwater sediment conditions and terrestrial plant production may result in greater submersed aquatic plant, algae and invertebrate production due to improved water clarity when reflooded (Sparks et ai., 1990; Sparks, 1992). Benefits are expected for vertebrates through trophic pathways beginning with high primary and microbia] production (Junk et al., 1989; Bay]ey, 1991; 1995). Adverse economic and recreational impacts can be minimized through co-ordination of river managers and users. As most commodities transported on the Upper Mississippi River Navigation System are agricultural in nature, impacts on shipping could be minimized by delaying drawdowns until after agrichemicals are transported north in the spring and ending them before crops are transported south to market the following autumn. Coal user impacts, the other major commodity shipped, could be reduced by stockpiling before navigation system closure. Other impacts to be addressed include petrochemical shipping and water withdrawal (industrial and municipal). The shutdown would provide opportunities for lock and dam and navigation fleet maintenance. Recreational users would be affected because traditional river access sites would not be functional. ShalJow marinas would be drained during drawdowns and boat ramps constructed to meet controlJed river stages would be 'high and dry'. Many of the favourite backwater fishing 'hot-spots' would be dry, and large fish kills would probably occur. In light of large economic and 'quality of life' issues at stake, there is a need to educate the public. Navigation interests and recreationists need to be educated about the role of hydrological disturbance in controlJing river-floodplain ecosystems (Junk et ai., 1989; Sparks et ai., 1990; Bayley, 1991; 1995; Sparks, 1995). They must be taught that temporary disturbances in the form of drawdowns are as necessary as floods to maintain healthy, productive river-floodplain ecosystems. Proposing this radical approach to Upper Mississippi River restoration serves two main goals. Firstly, discussion of system level restoration is initiated and secondly, a diverse array of river interests may come together to discuss their needs from the navigation system. I stress that this proposal requires good communication, education and co-ordination between river managers and users. It also requires thorough evaluation of ecological, economic and recreation factors before, during and following drawdown implementation. CONCLUSIONS A review has been presented of habitat rehabilitation and navigation channel maintenance projects designed to provide site-specific benefits to Upper Mississippi River aquatic habitats. I applaud on-going efforts for the information they provide, but stress that site-specific restoration will not restore the ecological integrity of the Upper Mississippi River. I propose an alternative solution that does not restore the full ecological integrity of the Upper Mississippi River, but does provide for low river stages that have been eliminated by navigation