Comparative sedimentation and geochemistry of three coves, Beaver Reservoir, northwest Arkansas

Sediment has been identified by the United States Environmental Protection Agency (USEPA) as the primary non-point source of water quality impairment in United States lakes and streams. Intense development pressures are a leading factor increasing sedimentation to water bodies throughout the U.S., including Beaver Reservoir of northwest Arkansas. Recently, several focused studies on Beaver Reservoir identified areas of substantial sediment deposition along with elevated levels of certain trace elements sequestered in the sediment. This dissertation focused on comparing sedimentation resulting from widespread land use transition from a primarily rural, agricultural landscape to one dominated by encroaching urban and high-density residential development in the Monte Ne Cove and Prairie Creek sub-watersheds of Beaver Reservoir. Blackburn Creek Cove, which drains a largely undeveloped sub-watershed, was also analyzed and served as a control to understand background sedimentation. In addition to identifying the impact of land cover change on sedimentation in the sub-watersheds, additional methods were employed to characterize the impact of the discharge of Drinking Water Treatment Residuals (DWTRs) to sediments in Monte Ne Cove. These additional methods were employed to better understand the DWTRs contribution to a definable volume and mass, along with any possible effect on the geochemical characteristics of the deposit.;Using a dual-frequency echo sounder in combination with extensive sediment probing, it was estimated that the Monte Ne, Prairie Creek, and Blackburn Creek sub-watersheds contained 195,830 m3, 83,159 m 3, and 56,978 m3 of sediment, respectively. At a mean density of 1.12 g cm-3 derived from lake sediment coring, this resulted in a total mass of 207,515 metric tonnes (T), 93,138 T, and 63,815 T respectively in the three coves. The Monte Ne sediments were further subdivided into two regions: one with a high probability of containing DWTRs (Region 1); one with a low probability of containing DWTRs (Region 2). A standard mixing equation based on dry bulk density was applied to the Region 1 sediments to partition the watershed-derived sediments from the DWTRs. It was found the Region 1 sediments contained 1,842 T of DWTRs, and 6,773 T of watershed-derived sediments. Interestingly, due to the significant differences in bulk density, the DWTRs comprised 67% of the volume of the Region 1 sediments, but only 21% of the mass. Overall, the DWTR comprised 6.3% of the volume and 0.89% of the mass of all Monte Ne Cove sediments. Comparing the results of the mass calculations from above with estimates of the mass discharged based on historic regulatory data validated this method. The linear sediment accumulation rate for the three sub-watersheds were 0.5 cm y-1 for Monte Ne, 0.3 cm y-1 for Prairie Creek, and 0.4 cm y -1 for Blackburn Creek. Comparatively, the mass accumulation rates were 0.55 g cm y-1 for Monte Ne, 0.33 g cm y-1 for Prairie Creek, and 0.44 g cm y-1 for Blackburn Creek. These results fit well with other recent Beaver Reservoir sedimentation studies, suggesting an overall low rate of sedimentation in the reservoir.;Land cover change was defined for the study area over the last four decades.;This study demonstrated the multi-disciplinary nature of reservoir sedimentation studies. Detailed understanding of the impact of land cover change on sedimentation required analysis of the resulting sediment quantity, quality, and source areas. The three-pronged approach utilizing high-resolution bathymetric data for sediment volumetric calculations, sedimentation modeling based on multiple historic land use datasets, and systematic geochemical analysis of the sediments has furthered our understanding of the impact of development on sedimentation pressures of Beaver Reservoir in these three coves. (Abstract shortened by UMI.)...