Watershed-scale features such as land use or size may affect the form and magnitude of carbon, nitrogen, or phosphorus watershed export. Similarly, watershed-scale processes (e.g., precipitation, hydrological regimes) may further mediate these fluxes. This dissertation focuses on three separate questions which address the effects of watershed-scale features and processes on biogeochemical fluxes via watersheds or within human-made impoundments.
Chapter 1: Hydrological controls on the export of carbon, nitrogen, and phosphorus from two contrasting Midwestern US watersheds. This study examines carbon (C), nitrogen (N), and phosphorus (P) export and C:N:P ratios from two watersheds using a high-frequency sampling regime over a two-year period. Particulate and dissolved as well as inorganic and organic forms were measured and the importance of hydrology (e.g. baseflow, storm events) to the export of these forms was assessed. Data show that storm events differentially affect the export of carbon and nutrient forms and that some C:N:P ratios vary greatly between the watersheds.
Chapter 2: Organic and inorganic carbon budgets in two human-made impoundments are controlled by watershed features and hydrology. This chapter explores the magnitude of organic and inorganic carbon inputs via streams, within-lake carbon dioxide atmospheric exchange, exports via the dam, and within-lake retention by creating mass-balance carbon budgets for two human-made impoundments of contrasting land use (agricultural versus forested). Results indicate that impoundments are net carbon sinks, but not large sinks or sources of atmospheric carbon dioxide.
Chapter 3: Local and global burial of organic carbon, nitrogen and phosphorus in small human-made impoundments. This chapter addresses the effectiveness of using watershed features to predict sediment carbon and nutrient concentrations, C:N:P ratios, and carbon and nutrient burial rates. Data show that morphometric watershed features are overall better predictors of sediment carbon, nitrogen, and phosphorus parameters than is watershed land use. Estimated rates of global organic carbon burial in these small impoundments contrast greatly with recent published data.