Altered hydrology resulting from the presence of locks and dams and erosive agricultural land use practices have created conditions that have impacted the growth, distribution, and survival of aquatic vegetation on the Upper Mississippi River System (UMRS). Three inter-related abiotic factors (light transparency, nutrients, and sedimentation) worsened by impoundment and erosive agricultural practices, have played a major role in widespread submersed macrophyte loss in the UMRS. Aquatic vegetation provides food and shelter for biota as well as impacting water quality. Successful efforts to restore aquatic macrophytes on the UMRS have focused on habitat restoration construction projects and water-level management drawdowns. Currently, the status of aquatic vegetation varies within the UMRS, with most of the aquatic vegetation being found between lower Pool 4 (below Lake Pepin) and Pool 13. Although aquatic macrophytes have varied among locations over the past 17 years, an increase in aquatic plants was apparent in 2007 and 2008. Very little research regarding the role of moist soil and emergent vegetation and their responses to ecological factors has occurred within the UMRS. Future research efforts must continue to focus on understanding the ecological and anthropogenic impacts to all aquatic macrophytes within the landscape of one of the largest river systems in the world.

The silver maple-American elm floodplain forest spans throughout the floodplains of the Upper Mississippi River System (UMRS). These forests of the UMRS today are less diverse than those of pre-European expansion (ca. early 1800s). Scientists and land managers are concerned about loss of species diversity including mast species such as pin oak (Quercus palustris Muenchh.), swamp white oak (Quercus bicolor Willd.), bur oak (Quercus macrocarpa Michx. Q), pecan (Carya illinoinensis (Wangenh.) K. Koch), and other hickories. The Great Midwest Flood of 1993 maintained species diversity in the lower, unimpounded region of the Upper Mississippi River, providing an opportunity for eastern cottonwood and black willow to regenerate in this portion of the Mississippi River. However, throughout the entire region, floodplain forests of the Upper Mississippi River have become less diverse, and have become dominated by the flood-tolerant and shade-tolerant silver maple (Acer saccharinum L.). The imminent loss of green ash (Fraxinus pennsylvanica Marsh.) to the Emerald Ash Borer (Agrilus planipennis Fairmaire) follows an already changing forest structure due to a disease-related shift of American elm (Ulmus americana L.) from the overstory to the midstory strata. Another invasive, reed canary grass (Phalaris arundinaceae L.), interferes with evolved mechanisms for establishment as it outcompetes trees of the early successional floodplain forest. Further research is needed to create and maintain diverse floodplain forest communities that have been lost under current conditions. Returning flood-prone agricultural lands within the floodplain to the floodplain forest will improve the health and connectivity of the river system, increase the diversity of habitats, and provide flood relief for communities of the Upper Mississippi River.

No abstract

Reports concerning the influence of dams on river hydrology vary among researchers, interest groups and government agencies. These often contradicting statements may occur because changes in hydrology caused by dams are distinct for each dam and river watershed. The objective of this research was to use site specific techniques to determine if the 1967 installation of the Carlyle Dam, lower Kaskaskia River, Illinois, altered flood frequency and duration within the forested floodplain located below the dam. Results indicated a decrease in flood duration and frequency, and a decrease in annual flood frequency variation at a site 6.4 km below the dam. Pre-dam versus post-dam differences in flood frequency and duration at the site 32.2 km below the dam were related to climate rather than dam effects. Although dam impacts are a concern, this research shows that distance downstream from the dam and downstream tributary and watershed characteristics should be considered before assuming that the dam has changed hydrologic parameters for portions of rivers. This research also indicates that areas of the lower Kaskaskia River may still maintain hydrologic ecological integrity, and could be targeted for restoration and adaptive management purposes. Hydrologic modelling combined with river gage and on-site well measurement techniques presented in this study could provide detailed flood frequency and duration information for land use, sociological and geomorphological questions in focus areas within river floodplains.