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

Persistent Link:
http://hdl.handle.net/10150/194215
Title:
Spatial and Temporal Hydrologic Variability as a Control on the Nutrient Dynamics of the Upper Rio Grande
Author:
Oelsner, Gretchen Pauline
Issue Date:
2007
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Large rivers in semiarid regions provide valuable resources for municipalities, agriculture, and adjacent ecosystems, yet the limited nature of the resource requires a concerted effort to understand the controls on water quality. To address this issue I continued and adapted biannual geochemical synoptic sampling of the Rio Grande from Del Norte, CO to Elephant Butte Reservoir between August 2003 and 2006 which had started in 2001. During average to drought conditions, river discharge was derived primarily from snowmelt in the headwaters region, total dissolved solutes increased downstream, and wastewater treatment plants were the largest source of nitrogen to the river. Surprisingly, return flows of river water diverted for agriculture had lower average nitrogen concentrations than the original river water, indicating that the agricultural system is a sink for nitrogen. When summer climatic conditions changed to a persistent monsoon regime, both the water and solute sources changed as the river was reconnected to its uplands and floodplain. Stable isotope data indicate that monsoon precipitation represented 10-50% of surface flow and that discharge increases were entirely due to ephemeral flows. An analysis of solute concentrations suggested that 80-100% of the increases in sulfate, chloride, DOC and nitrate were due to ephemeral flows. Ephemeral flows replaced wastewater treatment plants as the largest source of nitrogen to the river.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.
Type:
text; Electronic Dissertation
Keywords:
Hydrology
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Hydrology; Graduate College
Degree Grantor:
University of Arizona
Committee Chair:
Brooks, Paul D.

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleSpatial and Temporal Hydrologic Variability as a Control on the Nutrient Dynamics of the Upper Rio Grandeen_US
dc.creatorOelsner, Gretchen Paulineen_US
dc.contributor.authorOelsner, Gretchen Paulineen_US
dc.date.issued2007en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractLarge rivers in semiarid regions provide valuable resources for municipalities, agriculture, and adjacent ecosystems, yet the limited nature of the resource requires a concerted effort to understand the controls on water quality. To address this issue I continued and adapted biannual geochemical synoptic sampling of the Rio Grande from Del Norte, CO to Elephant Butte Reservoir between August 2003 and 2006 which had started in 2001. During average to drought conditions, river discharge was derived primarily from snowmelt in the headwaters region, total dissolved solutes increased downstream, and wastewater treatment plants were the largest source of nitrogen to the river. Surprisingly, return flows of river water diverted for agriculture had lower average nitrogen concentrations than the original river water, indicating that the agricultural system is a sink for nitrogen. When summer climatic conditions changed to a persistent monsoon regime, both the water and solute sources changed as the river was reconnected to its uplands and floodplain. Stable isotope data indicate that monsoon precipitation represented 10-50% of surface flow and that discharge increases were entirely due to ephemeral flows. An analysis of solute concentrations suggested that 80-100% of the increases in sulfate, chloride, DOC and nitrate were due to ephemeral flows. Ephemeral flows replaced wastewater treatment plants as the largest source of nitrogen to the river.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.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
dc.subjectHydrologyen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineHydrologyen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.chairBrooks, Paul D.en_US
dc.contributor.committeememberHogan, James F.en_US
dc.contributor.committeememberMeixner, Thomasen_US
dc.contributor.committeememberTidwell, Vinceen_US
dc.contributor.committeememberGuertin, D. Phillipen_US
dc.identifier.proquest2366en_US
dc.identifier.oclc659748249en_US
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