| The primary objectives of this dissertation are to (1) provide a snapshot of the hydrogeoecological condition of the upper and middle Rio Grande in Colorado and New Mexico for the period 1975--2002; (2) to consider the dynamics that shaped that condition; and (3) to consider some of the ecological consequences of it.; Chapter one addresses patterns and trends in discharge, specific conductivity (SC), total dissolved solids (TDS), pH, Ca2+, Na+, Mg2+, K+, HCO3-, SO42-, Cl-, F -, and SiO2.; Results show (1) increasing discharge over the study period due to a period of regionally increased precipitation; (2) increasing temporal trends in many geochemical parameters at upstream stations; (3) decreasing temporal trends in many geochemical parameters at downstream stations; (4) an increasing temporal trend in pH at downstream stations, attributed to improvements in sewage treatment; (5) an increasing temporal trend in fluoride, attributed mostly to increased pumping from high-fluoride groundwater sources and subsequent return to the river; (6) and a spatial pattern of increasing concentrations of many parameters at the city of Albuquerque, indicating the high impact the city has on river chemistry.; Chapter two addresses patterns and trends over the same time period and at the same USGS stations for organic carbon (total), N-NH4+ + organic N (total), NH4+ (dissolved), N-NO2 - + N-NO3- (dissolved), phosphorus (total), and P-orthophosphate (dissolved). I explore the deleterious impact that drought or low seasonal flows can have on arid land rivers with large sewage effluent inputs. Comparison with other rivers of the American Southwest shows that concentrations for most nutrient parameters in the Rio Grande are relatively low.; Chapter three uses system dynamics modeling to address the ecological dynamics associated with sewage effluent discharged to the Rio Grande from the city of Albuquerque. Results show that toxic ammonia concentrations were above levels considered to have acute impacts on aquatic life occassionally from 1989 to 1992, and they were above levels considered to have chronic impacts frequently over the same years. Modeled ammonia concentrations generally declined from 1989--2002, due to improved sewage treatment. I conclude that ammonia concentrations played an important role in Middle Rio Grande ecology during and previous to the study period, they contributed to the extirpation of minnow species from the Rio Grande, and they contributed to the endangerment of the Rio Grande silvery minnow. (Abstract shortened by UMI.)... |
