Spatial and Temporal Hydrologic Variability as a Control on the Nutrient Dynamics of the Upper Rio Grande

Using data from the synoptic sampling, I developed both a simple chloride mixing model and a dynamic simulation model of nitrate to evaluate the controls on nutrient cycling within the Rio Grande. Results from the chloride mixing model indicate that both abiotic hydrologic processes and biotic processes provide important controls on nutrient concentrations. River characteristics that increase surface water/groundwater exchange are important for determining nutrient retention, a result commonly identified in smaller streams, but never before quantified in a large river. Dynamic simulation modeling indicates that both plant uptake and denitrification remove nitrate within the Middle Rio Grande with denitrification accounting for 55-100% of the nitrate removal downstream of Albuquerque. The results of this dissertation provide a conceptual model for the hydrologic and biologic controls on nutrient concentrations in a heavily managed large semiarid river.