Biological Soil Crust
Drylands cover greater than 40% of the land surface on earth, and due to critical relationship between soil moisture and biological growth, these environments are particularly sensitive to climate change. We are studying biological soil crusts (biocrusts) from drylands in Utah, Idaho, New Mexico, and Texas that span arid, semiarid, and dry sub-humid climate zones. We are evaluating relationships among biogeochemical and metabolic responses to climate and landscape variables to better understand the effects of climate change on dryland ecosystems. Biocrusts affect interactions between the atmosphere and solid earth, and biocrusts have an outsized role in dryland nutrient dynamics. Thus, a relatively small change in mean annual precipitation or seasonality can have a large effect on dryland critical zone function. We are using diverse lipid classes as tools to address the roles of biocrust organisms in the dryland carbon cycle. Intact polar lipids (IPLs), triacylglycerols, free fatty acids, oxylipins and oxy-IPLs include structures with taxonomic specificity, carbon storage capacity, oxidative stress response, response to nutrient limitation, and signaling properties. We have identified lipids that correspond with mean annual precipitation, total organic carbon storage, and soil extractable phosphate concentration. The analysis of multiple classes of bioactive lipids is a promising approach to describing microbial populations and their association with water and nutrient availability in biocrust using a relatively rapid screening technique.
Microbial Mats
Microbial mats are stratified communities that represent the oldest known ecosystems. These systems are widespread, covering many coastal areas and tidal flats. However, their carbon fluxes and ultimately their contributions to the carbon cycle are not fully constrained. Our analysis is focused on the oxidation state of bulk mat organic carbon and of lipid biomarkers. We propose that redox conditions imprinted by tidal position and incident solar radiation are primary drivers in microbial mat carbon preservation, and oxidation states are effective ways of characterizing the degradation of organic matter. Auxiliary data in the form of photopigments, metagenomes, reactive oxygen species, and organic acids further constrain the microbes responsible for carbon storage as well as the overarching redox conditions of the mat system.
Anoxic Environments
We are currently studying organic-carbon-rich sedimentary rocks associated with the Hangenberg mass extinction event. The Hangenberg event was the final phase of the Late Devonian extinction interval, when greater than 50% of genera became extinct. It occurred during the transition from the Devonian to the Carboniferous periods, when anoxia was widespread in the oceans. At that time, the Western Canada Sedimentary Basin (WCSB) in Alberta was located in the tropics and broadly anoxic. Our analysis is focused on the organic geochemistry (biomarkers by GC/MS and porphyrins by LC/MS) and stable isotopic composition (C and N) of Exshaw Formation rocks from 20 locations in the WCSB. We are also analyzing sedimentology, stratigraphy, and inorganic geochemistry to provide sedimentary context as we develop models for the spatial distribution of biogeochemical processes in ancient epeiric seas. For the WCSB, we propose that coastal and equatorial upwelling and advection of water masses affected different modes of biogeochemical nutrient cycling across the sea. Similar biogeochemical heterogeneity is seen in modern oceans and likely occurred in other ancient ocean basins.
Geoarchaeology
Our lab provides support for the geochemical analysis of archaeological remains. We are affiliated with the Baylor University San Giuiliano Archaeological Research Project, a research program based in San Giuliano, Italy. The excavation site includes Etruscan tombs and architecture and a medieval settlement. Working with students studying archaeology and anthropology, we have conducted field analyses using a Bruker Tracer 5i energy-dispersive portable X-ray fluorescence spectrometer (pXRF). This work contributed to publications on Medieval Glass and and the Tomb of an Etruscan girl.
We are also collaborating with researchers studying animal remains from the ancient Philistine city of Ashkelon, in modern Israel. We are using carbon, oxygen, and strontium isotopes of tooth enamel to assess diet and herd management strategies related to past variability in the climate of the Levant.