Torres-Poche, Zaria (2017-07). 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.
Thesis
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 (?13C) and nitrogen (?15N) 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 ?D 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 ?13C and ?15N. I also compared historic and contemporary APC feather ?13C and ?15N 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 ?13C and ?15N from blood, the main diet source is C3 vegetation (forbs) when 3, 4, and 5 diet sources are used. Historic feather's ?13C and ?15N values showed that spiders (3 and 4 diet sources) and rice (5 diet sources) contributed the most to APC diet. Contemporary feather ?13C and ?15N values determined insects (3 sources), forbs (3 sources), and C4 vegetation (grasses; 5 sources) contributed the most.
