Persistent Link:
http://hdl.handle.net/10150/279931
Title:
Aspects of ecosystem health in the Colorado River Delta, Mexico
Author:
Garcia Hernandez, Jacqueline
Issue Date:
2001
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:
Two aspects of ecosystem health in the Colorado River delta were investigated as part of the present dissertation. The following is a summary of the most important findings: Contaminants of natural origin (e.g. selenium) and anthropogenic activities (e.g. pesticides) represent a potential threat for humans and wildlife in the Colorado River delta. Fourteen locations were sampled for bottom material and biota from March 1998 to April 2000. Concentrations of selenium in bottom material ranged from 0.6-5.0 μg/g. Concentrations of selenium in biota ranged from 0.5-18.3 μg/g, 23% of these samples exceeded the toxic threshold where reproductive impairment in birds from dietary exposure is reported. Concentrations of DDE exceeded the lower critical dietary level for sensitive species in 30% of biota samples. No clear relationship could be found between the concentration of Se in bottom material and the concentration of Se in fish. Nevertheless, smaller Se concentrations in biota were found at sites that had an outflow and exposure or physical disturbance of the bottom material was uncommon. Greater concentrations of Se in biota were found at sites with strongly reducing conditions, no output, and subsequent periods of drying and flooding or dredging activities, and at sites that received water directly from the Colorado River. The southwestern willow flycatcher (Empidonax traillii extimus ) is an endangered neotropical migrant with only 300-500 breeding pairs. The objective of the second study was to determine the presence/absence of this bird in the Colorado River delta. Surveys were conducted from June to July, 1999 and from May to June, 2000 using an audio tape of this subspecies' songs to elicit responses. We detected a total of 50 willow flycatchers in the Colorado River delta in the months of May to June. None were detected in July, thus, the birds were most likely migrants. Restoration of the intensively used stopover sites of the Colorado River delta appears to be essential for the overall recovery of this subspecies. Additionally, we propose a possible willow flycatcher summer migratory route throughout the series of coastal estuaries found adjacent to the coast of Sonora.
Type:
text; Dissertation-Reproduction (electronic)
Keywords:
Biology, Ecology.; Environmental Sciences.
Degree Name:
Ph.D.
Degree Level:
doctoral
Degree Program:
Graduate College; Soil, Water and Environmental Science
Degree Grantor:
University of Arizona
Advisor:
Glenn, Edward P.

Full metadata record

DC FieldValue Language
dc.language.isoen_USen_US
dc.titleAspects of ecosystem health in the Colorado River Delta, Mexicoen_US
dc.creatorGarcia Hernandez, Jacquelineen_US
dc.contributor.authorGarcia Hernandez, Jacquelineen_US
dc.date.issued2001en_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.abstractTwo aspects of ecosystem health in the Colorado River delta were investigated as part of the present dissertation. The following is a summary of the most important findings: Contaminants of natural origin (e.g. selenium) and anthropogenic activities (e.g. pesticides) represent a potential threat for humans and wildlife in the Colorado River delta. Fourteen locations were sampled for bottom material and biota from March 1998 to April 2000. Concentrations of selenium in bottom material ranged from 0.6-5.0 μg/g. Concentrations of selenium in biota ranged from 0.5-18.3 μg/g, 23% of these samples exceeded the toxic threshold where reproductive impairment in birds from dietary exposure is reported. Concentrations of DDE exceeded the lower critical dietary level for sensitive species in 30% of biota samples. No clear relationship could be found between the concentration of Se in bottom material and the concentration of Se in fish. Nevertheless, smaller Se concentrations in biota were found at sites that had an outflow and exposure or physical disturbance of the bottom material was uncommon. Greater concentrations of Se in biota were found at sites with strongly reducing conditions, no output, and subsequent periods of drying and flooding or dredging activities, and at sites that received water directly from the Colorado River. The southwestern willow flycatcher (Empidonax traillii extimus ) is an endangered neotropical migrant with only 300-500 breeding pairs. The objective of the second study was to determine the presence/absence of this bird in the Colorado River delta. Surveys were conducted from June to July, 1999 and from May to June, 2000 using an audio tape of this subspecies' songs to elicit responses. We detected a total of 50 willow flycatchers in the Colorado River delta in the months of May to June. None were detected in July, thus, the birds were most likely migrants. Restoration of the intensively used stopover sites of the Colorado River delta appears to be essential for the overall recovery of this subspecies. Additionally, we propose a possible willow flycatcher summer migratory route throughout the series of coastal estuaries found adjacent to the coast of Sonora.en_US
dc.typetexten_US
dc.typeDissertation-Reproduction (electronic)en_US
dc.subjectBiology, Ecology.en_US
dc.subjectEnvironmental Sciences.en_US
thesis.degree.namePh.D.en_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.disciplineSoil, Water and Environmental Scienceen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorGlenn, Edward P.en_US
dc.identifier.proquest3002541en_US
dc.identifier.bibrecord.b41434249en_US
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