Due to habitat degradation and overharvest (Colombo et al. 2007) sturgeon populations are declining throughout their global distribution (Pikitch et al. 2005). In North America, five sturgeon species are listed as endangered or threatened due to overharvest and habitat degradation. One species of direct concern is the pallid sturgeon (Scaphirhynchus albus ) (Boreman 1997). The morphologically similar shovelnose sturgeon (S. platorynchus) is not listed as endangered but has become a cause for concern due to poor reproductive success and declining recruitment of their offspring to the adult population, likely a result of lack of proper spawning habitat and early life foraging opportunities (Wildhaber et al. 2007). Despite listing the pallid sturgeon as endangered and increasing concern about population decline, little information is available about the foraging ecology of age–0 Scaphirhynchus sturgeon. To ensure these sturgeon populations persist in the Middle Mississippi River, a better understanding of sturgeon foraging success during early life is imperative. I quantified age–0 Scaphirhynchus sturgeon (total length (TL) range: 14–200 mm; small < 50 mm TL, large 50–200 mm TL) diets during 2004–2008 to determine whether foraging behavior changed as a function of stage height, water temperature, water velocity, size class of sturgeon, and macrohabitat. I also examined whether energy density (cal/g) and selection of prey varied across size class and macrohabitat. Age–0 Scaphirhynchus sturgeon were collected from the Middle Mississippi River during spring (March, April, May), summer (June, July, August), and fall (September, October, November). Each prey item in diets was identified to family and measured to calculate dry weight. Ephemeroptera, Diptera pupae, and Chironomidae were the dominant taxa that were consumed across all years and seasons. Large sturgeon had a broader diet, consuming more non–dominant taxa. Abiotic factors differed across macrohabitats and thus influenced foraging behavior. Sturgeon occupying the island upstream tip (IUT) macrohabitat had the largest mean mass in diet and those at the island downstream tip (IDT) had the lowest mean mass in diet. Conversely, energy density of sturgeon was highest at IDT and lowest at IUT. Small sturgeon avoided macroinvertebrates that were outside the dominant prey taxa whereas large sturgeon selected for Chironomidae across all macrohabitats. Diets of age–0 Scaphirhynchus sturgeon vary as a function of size and are influenced by interacting of abiotic and biotic factors at each macrohabitat. As age–0 Scaphirhynchus sturgeon grow, their diet broadens. Diet of young sturgeon interacts with energy condition in counterintuitive ways that requires more study. Because foraging success differs among habitats and is likely linked to recruitment, habitat quality and quantity in the Middle Mississippi River is likely critical for sturgeon population density and growth.

By combining FEMA's HAZUS-MH (Hazards U.S. Multi-Hazard) flood-loss estimation software and the HEC-RAS hydraulic modeling package, this study was able to quantify potential beneficial and adverse impacts of flood-control and navigational structures along the Middle Mississippi River (MMR; between Mississippi-Missouri River confluence and Thebes, IL). The goal of this investigation was to assess changes in water-surface elevations and associated flood losses to: 1) quantify the potential exposure of flooding under different flood-control configurations along the Middle Mississippi River (MMR), and 2) assess the relative contributions of various engineered structures and flood-loss strategies to potential flood losses. Assessment of the impact of engineering structures was accomplished by modeling five scenarios for the 100- and 500- year floods: 1) current MMR levee configuration (levee protecting for ≤50-year flood); 2) removal of all flood-control structures on the MMR; 3) increasing the height of levees and floodwalls in metropolitan St. Louis to protect urban areas to the 500-year flood level while simultaneously removing all agricultural levees downstream; 4A) a less engineered MMR channel and floodplain with fewer flood control and navigation structures, simulating conditions from 65 years ago (1942-1947) with 1940's levees; and 4B) a less engineered MMR channel and floodplain with fewer flood control and navigation structures, simulating conditions from 65 years ago (1942-1947) with current levee configuration. Comparison of scenarios 2 and 3 relative to scenario 1 allows for quantitative assessment of the flood-control structures on stages and flood losses. Results from scenario 2 revealed that removing all levees along the MMR reduces the average stages from 2.2 m (100-year) to 2.5 m (500-year, but also increased economic and social impacts relative to scenario 1. Scenario 3 revealed that removing agricultural levees downstream of St. Louis on the MMR decreased stages by 1.4 m (100- and 500-year); however, flood losses for the 100-year flood were increased. Flood losses for the 500-year flood were decreased relative to scenario 1. These results suggest that agricultural levees along the MMR protect against medium size floods (50- or 100-year flood) but cause more damage than they prevent during large floods such as the 500-year flood. Comparison of scenarios 4A and 4B relative to scenario 1 allows for a quantitative assessment of river engineering structures and modern buildings constructed over the last 65 years. In scenarios 4A and 4B, a less engineered river decreased stages by 1.2 m (for the 100-year flood) relative to scenario 1. In scenario 4A, the 1940's levees expose modern buildings in the floodplain to flooding, causing economic building losses to increase; however, in scenario 4B, current levee configuration protects modern buildings in the floodplain from flooding causing, economic building losses to decrease. If the current flood-control structures were not built, it is likely that the land in the floodplain for scenarios 4A and 4B would not be developed and the land used would be more flood-tolerant. Sensitivity analyses were run to assess the impact of using the default HAZUS-MH national-level data; this was done by comparing results produced by using aggregate analysis (coarse data) versus results using UDF analysis (detailed data). The aggregate analysis estimated 51% fewer buildings damaged than the UDF analysis. Conversely, the aggregate analysis increased the economic building losses by 51% relative to the UDF analysis. Although collecting local data for a study is not always feasible, the large differences documented here need to be considered when discussing HAZUS-MH results. Overall, this project shows implications for historic and future flood-control and navigational structure projects on the MMR and other rivers. It also emphasizes the importance of studying the impact future engineering structures will have on water-surface elevations and flood losses before implementing them.

The construction of levees along the Mississippi River [MR], beginning in the mid-to-late nineteenth century, have isolated the river along many segments from its floodplain. Sediment from the river is currently deposited in the hydrologically connected floodplain [HCF], the area between the channel margin at low water and the levees. Researchers have studied the amount and rates of sediment deposition along the Upper and Lower Mississippi River segments from the headwaters to Pool 22 and from the Ohio River to the delta; however, no such assessments have been undertaken along the Middle Mississippi River [MMR]. This study attempts to fill the knowledge gap by assessing sedimentation along three islands within the Middle Mississippi River National Wildlife Refuge. On these islands two approaches were undertaken to assess sedimentation along the MMR’s HCF: dendrogeomorphology and the DEM of Difference [DoD] approach. The dendrogeomorphic approach uses tree-ring analyses to document and interpret geomorphic processes and the rates at which they are occurring. The DoD approach subtracts an older DEM from a newer DEM in order to see the change in elevation/depth over time. The geomorphology of the islands and then the entire MMR HCF (from the confluence of the Missouri River to Thebes, IL) were mapped. Using the sedimentation rates for the geomorphic landforms from the three study islands, the sedimentation rates and volumes for the aforementioned portion of the MMR’s HCF were estimated. The estimated volume of sediment was then compared to the MMR’s suspended sediment flux to determine how much of the suspended sediment was going into storage within the MMR’s HCF. The dendrogeomorphic and DoD methods for the study islands yielded average sedimentation rates of 13.3-16.9 mm year-1 and 21.5-80.1 mm year-1, respectively. The rates for the individual landforms on the islands using the dendrogeomorphic results ranged from 5.2 mm year-1 for the splay to 21.8 mm year-1 for the natural levee and splay, with a weighted average of 16.6 mm year-1 for the MMR HCF. Using these rates and the likely range of densities for the floodplain sediments, it is estimated that 4.9-6.6 million metric tons of sediment is accumulating within the MMR annually. This is approximately 5.4-7.4% of the average annual suspended sediment load of the Mississippi River at St. Louis. This means that the MMR is a major sediment sink. If these relatively rapid rates of deposition continue, they have the potential to substantially reduce the HCF’s ability to convey and store flood water which will result in increased flood levels and, consequently, flood risk within the MMR’s levee protected floodplain in the coming decades.