Annette Summers Engel
Jones Professor of Aqueous Geochemistry
University of Tennessee at Knoxville
Department of Earth and Planetary Sciences
Engel Lab Research 
Our interdisciplinary research spans the study of cave and karst aquifer evolution and speleogenesis, the role of natural organic matter in karst, and the biodiversity of caves, as well as the relationships among aquatic marine organisms and their interactions with ocean environments, oil degradation and trajectories following disturbances, and chemosymbiotic and symbiotic associations with clams, invertebrates, and even alligators.
The following sections summarize each of the ongoing research projects. Follow the links for more information:
Linking community and food-web approaches to restoration: An ecological assessment of created and natural marshes influenced by river diversions

This research will determine the food web structure of microorganisms, plants, invertebrates, and fishes using cutting-edge isotopic, genomics, and modeling approaches for natural marshes along varying salinity levels that result from a Mississippi River diversion, and also at created marshes that differ in age and that are also influenced by a river diversion. 
Effects of the Macondo Oil Spill on Coastal Ecosystems: Microbial oil degradation and diversity trajectories after the Deepwater Horizon oil spill disturbance 
This research project started immediately after the April 2010 blowout of the Macondo 252 well and explosion of the Deepwater Horizon (DWH) platform. The goal of the research was to understand what changes (if any) would occur at the microbial level in geochemically variable, shallow marine environments (e.g., sandy beaches, marshes, oyster beds) before and following the oil spill. 
Dimensions of Lucinid Chemosymbiotic Associations
Lucinids are common infaunal bivalves in shallow coastal marine habitats, including seagrass meadows and mangrove forests, where they position themselves near the oxic-anoxic interface. Lucinids are the most taxonomically diverse clade of chemo-symbiotic bivalves. Our research at UTK includes characterizing the geochemical, ecological, and sedimentological properties of sediments in lucinid habitats, microbial diversity analyses from sediments and hosts, and evaluation of 'omics data. 
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Speciation and Behavior of Sulfur Gases in Biogeochemical Processes
Interpreting past geochemical and ecological changes from bulk isotopic analyses of S-bearing deposits can be misinterpreted if the speciation of S compounds is not done. One of the most complicating issues regarding S cycle processes is how S gases affect S speciation during deposition or diagenetic alteration. At the LSU Center for Advanced Microstructures and Devices (CAMD) facility, we designed a way to measure the S K-edge X-ray absorption near-edge structure (XANES) spectroscopy of S gases.
Deciphering the evolutionary history and metabolisms of Epsilonproteobacteria
Despite ongoing attention given to pathogens within the class Epsilonproteo-bacteria, environmental members are still among the most poorly characterized bacteria. There are unresolved evolutionary relationships between marine and terrestrial lineages, as well as between lineages found in cold and hot habtiats, and habitats that are freshwater versus saline.
Biodiversity of caves and karst in the Valley and Ridge
One of the richest karst areas in the United States is in TAG (Tennessee, Alabama and Georgia), with Tennessee currently ranking 2nd to Texas for the most obligate subterranean species. Tennessee currently has more mapped caves than any other state, at over 10,000. However, recent only 5% of Valley and Ridge caves (of ~500 caves) have fauna records. Almost nothing is known about the microbiology of caves in Tennessee. We are exploring at least 100 caves to address sampling gaps.
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Arsenic cycling in geothermal waters
El Tatio in Northern Chile is located at 4440 m in the hyper-arid Atacama Desert and comprises one of the largest geyser zones known. Naturally sourcedarsenic support 
thermophilic microbial communities that
survive intense solar radiation by living in siliceous sinter. We measure metal-coordination, speciation, and oxidation/ reduction states of As, Sb, and Fe using XANES and EXAFS , ATR-FTIR, and fluorescence spectroscopy, as well as characterize the microbial communities and functional genes. 
Microbially mediated karst aquifer evolution and speleogenesis
Over the past decade, our research has focus on the Edwards Aquifer in Central Texas, and the fresh water and saline water interface (FWSWI). Freshwater meets
hydrogen sulfide-rich water, and FWSWI microbes cause carbonate dissolution. Biofilms also serve as food sources for aquifer animals proximal to the FWSWI. Changes in microbial food sources and food web structures are evident from C and N isotopic signatures of invertebrates
Dissolved Organic Matter Transformations in Karst
This research focuses on understanding geochemical and enzymatic controls that affect microbial transformations of DOM as water moves from the surface into the subsurfac, including changes functional microbial diversity (i.e. at the level of genes and enzymes). We use spectroscopy, wet chemistry, and molecular methods to conduct the research.
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Funding acknowledgements

Our research is currently supported by the National Science Foundation, the Gulf of Mexico Research Initiative, the NOAA RESTORE Science Program, the Cave Conservancy Foundation, and the University of Tennessee (department and Jones endowment funds). Previous research has been supported by the National Science Foundation, the Louisiana Board of Regents, and generous anonymous donors. Student research and travel expenses have been supported by the American Association of Petroleum Geologists, the Geological Society of America, the Coastal and Estuarine Research Federation, and Sigma Xi.
Geochemistry. Geomicrobiology. Geology. Ecology.

Interdisciplinary Research at the University of Tennessee