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Evaluating the Impacts of Metals on Aquatic Birds in Lake Chapala, and the Use of Stable Isotopes for Predicting the Attwater’s Prairie-Chicken Diet
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The largest tropical lake in Mexico, Lake Chapala, is a major fishery and a recipient of many contaminants (industrial and agricultural) via the Lerma River. The objectives were to evaluate concentrations of mercury (Hg), aluminum (Al), barium (Ba), copper (Cu), manganese (Mn), strontium (Sr), vanadium (V), and zinc (Zn) in fish and wildlife of Lake Chapala. I also used stable isotopes carbon (δ¹³C) and nitrogen (δ¹⁵N) to determine trophic differences between the 3 collected fish species. I collected water, sediment, fish, and feather samples and measured these samples for Hg and other metals. Mercury concentrations in water were higher compared to other lakes around the world, but not as high as those determined from the Jose Antonio Alzate reservoir in Mexico. Sediment Hg concentrations were similar to those reported by other studies from Lake Chapala. Also, the Hg concentrations measured in fish were similar to those from other studies. Feather samples collected had a wide range of δD values; therefore using these values were not useful for predicting significant relationships between areas of feather growth and areas of Hg acquisition. Concentrations of other metals in water, sediments, and fish were also similar to those reported in previous studies. An Attwater’s prairie-chicken (APC) study was conducted to determine the diet of wild APC populations once released from captivity with the use of stable isotope analysis of δ¹³C and δ¹⁵N. I also compared historic and contemporary APC feather δ¹³C and δ¹⁵N values to one another. I collected vegetation, insect, fecal, and blood samples from APCs on the Attwater Prairie Chicken National Wildlife Refuge (APCNWR). The stable isotope analysis revealed the mixing model produces different results dependent on the number of diet sources used. When analyzing δ¹³C and δ¹⁵N from blood, the main diet source is C₃ vegetation (forbs) when 3, 4, and 5 diet sources are used. Historic feather’s δ¹³C and δ¹⁵N values showed that spiders (3 and 4 diet sources) and rice (5 diet sources) contributed the most to APC diet. Contemporary feather δ¹³C and δ¹⁵N values determined insects (3 sources), forbs (3 sources), and C₄ vegetation (grasses; 5 sources) contributed the most.
Torres-Poche, Zaria (2017). Evaluating the Impacts of Metals on Aquatic Birds in Lake Chapala, and the Use of Stable Isotopes for Predicting the Attwater’s Prairie-Chicken Diet. Doctoral dissertation, Texas A & M University. Available electronically from