Nowlin, WestonCorrington, Chase2022-04-182022-04-182022-05Corrington, C. A. (2022). <i>Spatial gradients and food web structure of groundwater communities</i> (Unpublished thesis). Texas State University, San Marcos, Texas.https://hdl.handle.net/10877/15667The Edwards Aquifer (EA) and its springs in Texas are some of the most biologically unique and diverse subterranean-surface coupled systems on the planet, containing many endemic and endangered crenic and hypogean species. However, relatively little is known about the spatial patterns of diversity and trophic ecology of groundwater dependent species in the northern (Barton Springs) segment of the EA. Microbial chemolithoautotrophy (MCLA) is an important source of organic matter (OM) for some aquatic organisms in the southern EA, but the importance of MCLA is unknown in the northern EA. We examined spatial patterns of geochemistry, stable isotope values of particulate OM, and stygofaunal community structure across the northern EA. We also examined the diet of the endangered crenic Barton Springs salamander (Eurycea sosorum) and subterranean Austin Blind salamander (Eurycea waterlooensis) at Eliza Springs (a major spring) using stable isotopes. We found spatial variation in geochemistry in the northern EA, but OM isotopic composition did not vary with geochemistry, suggesting that MCLA was not a major contributor to OM production. Dietary mixing models found that copepods were the most important diet item for both salamander species, with ~60% both species’ diets consisting of hypogean organisms. Isotopic niche analyses indicate substantial overlap between salamander species, which has conservation implications for these endangered species, as well as ecosystem functioning of the EA as a whole.Text63 pages1 file (.pdf)enBarton Springs segmentChemolithoautotrophyreshEdwards AquiferFreshwater saline water interfaceMANOVANorthern segmentPCAParticulate organic matterRDASan Antonio segmentStable isotopesTrophic enrichment factorThesis