Investigating Historic and Modern Reservoir Ecology at Whole Watershed and Singular Basin Scales with Sediment Paleolimnological Techniques

Abstract

Reservoirs or dammed river systems are prevalent both around the globe and in the Southeastern United States. They provide many ecosystem services (e.g., flood mitigation, water storage, navigation, recreation) at the cost of potential disruption to the natural environment. For example, reservoirs deposit and trap large amounts of river sediments, serve as growth incubators for primary producers, encourage biogeochemical flux, and prevent organismal migrations among other negative impacts. Because of these impacts, reservoirs have become of greater importance, thus prompting scientific investigations. In this dissertation, three areas were addressed: sediment record age models were tested and evaluated for usability in reservoir paleolimnological research, how reservoirs' nitrogen flux/deposition is altered by external impacts, and how heavy metals and the cyanotoxin, cylindrospermopsin, are distributed throughout a hydrologically complex reservoir system. In Chapter 2, I found that the four age models tested—constant rate of supply, mass balance, Bacon, and Plum—all provided usable dates for core sections, but utility varied with research questions and applications. In Chapter 3, results showed that average annual residence time had the strongest relationship to nitrogen deposition. Furthermore, I found long-term droughts increase reservoir residence times by 45–60% and intensified nitrogen cycling through primary productivity in reservoirs. In Chapter 4, results showed that sedimentary contaminant distribution was heterogeneous, with heavy metals deposited along with organic matter and cylindrospermopsin concentrations more associated with the presence of cumulative fine sand. These findings demonstrate the complexity and benefit of sediment investigations and highlight the reservoir sedimentary environment as a hotspot of material storage and historic information.