Biology ETDs

Publication Date



The Rio Grande has been identified as one of the most endangered rivers in the United States by American Rivers. Biologically, the consequences of the massive anthropogenic alterations of this river have been substantial. The overall aim of this study was to characterize the ecological implications of these alterations in the aquatic food web of the middle Rio Grande (MRG) of New Mexico. Our approach was to analyze the stable isotope composition of current food web components and of historical museum preserved fish specimens. After determining that we could use stable isotope analyses of historical museum preserved fish specimens (chapter 1), we proceeded with our study on the current food web of the MRG. The results of this study allowed us to develop a food web model of the MRG. Regardless of sample site or season, autochthonous production was the dominant carbon source in our system. Fishes sampled from the MRG are not supported directly by primary producers, but instead by an intermediate step consisting of either macro- or micro-invertebrates. Omnivory is evident in the contemporary fish food web, as fishes used similar resources regardless of nominal dietary differences. In addition, we observed enhanced food web dependence on autotrophic production at one of our sites (Bernardo), which may be linked to anthropogenic inputs of nutrients. In the final portion of this study, we characterized the historical food web, and found many similarities with our current-day food web results. Omnivory has dominated the fish food web for the past 60 years, and may be contributing to food web stability in the face of anthropogenic change. Overall, carbon and nitrogen stable isotope values of fish changed little over time. The exception to this is at our Bernardo site, which displays enhanced autotrophy in the later years, similar to our results in the current food web. The timing of the switch to autotrophy at Bernardo coincides with an expansion of the Albuquerque Wastewater Treatment Plant, which may be contributing soluble nutrients and driving eutrophication.



Document Type


Degree Name


Level of Degree


Department Name

UNM Biology Department

First Committee Member (Chair)

Thomas F. Turner

Second Committee Member

Manuel C. Molles Jr.

Third Committee Member

Clifford Dahm

Fourth Committee Member

Zachery Sharp

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Biology Commons