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ARS Home » Plains Area » Sidney, Montana » Northern Plains Agricultural Research Laboratory » Pest Management Research » Research » Publications at this Location » Publication #412349
Research Project: Biological Control and Habitat Restoration for Invasive Weed Management

Location: Pest Management Research

Title: Heavy metal-based bat guano chronologies: A cautionary tale

Author
item TSALICKIS, ALEXANDRA - Auburn University
item WATERS, MATTHEW - Auburn University
item Campbell, Joshua
item VACHULA, RICHARD - Auburn University

Submitted to: The Holocene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/5/2025
Publication Date: 10/9/2025
Citation: Tsalickis, A., Waters, M.N., Campbell, J.W., Vachula, R.S. 2025. Heavy metal-based bat guano chronologies: A cautionary tale. The Holocene. 1-5. Article 09596836251378031. https://doi.org/10.1177/09596836251378031.
DOI: https://doi.org/10.1177/09596836251378031

Interpretive Summary: Bat guano has gained recognition as a reliable paleoenvironmental archive in recent decades but to reconstruct paleoenvironmental conditions using bat guano, an age depth model is required. While radiocarbon dating is the most acceptable method for determining chronologies, it is not possible to use on modern aged (i.e., post 1950 CE) bat guano, therefore a reliable method for dating post-bomb and post-industrial guano deposits is needed. Heavy metals are an untested means of dating post-bomb guano deposits. Here, we use peaks of heavy metal concentrations of lead (Pb), molybdenum (Mo), and chromium (Cr) to identify singular dates within a bat guano core collected from Cripps Mill Cave in Tennessee, USA. One peak in Pb concentration is interpreted to indicate 1974 CE, synchronous with peak leaded gasoline combustion in the United States. Three peaks in Mo concentrations in the Cripps Mill guano core correspond to Mo concentration peaks in ice cores and date to 1975, 1980, and 1989 CE, respectively. These peaks reflect increased Mo concentrations sourced from anthropogenic coal and oil combustion. Utilizing the interpreted dates we created an age-depth model for the Cripps Mill guano core. Further, we show and discuss the utility of our approach in two additional guano cores from the southeastern US. Our approach shows that heavy metal peaks are an effective method for dating modern post-bomb guano deposits, opening new opportunities for linking guano-based paleoenvironmental research with modern, post-bomb observations.

Technical Abstract: Bat guano can provide a unique way to examine past environmental records but a method to date the guano is needed. We examined a bat guano core collected from a cave in Alabama, USA for nitrogen and carbon isotopes. Modern aged guano (post 1950) cannot be aged via radiocarbon. Various heavy metals could be a unique alternative to date modern guano. We used peaks of heavy metal concentrations of lead (Pb), molybdenum (Mo), and chromium (Cr) to identify dates within a bat guano core collected from a cave in Tennessee, USA. The Pb peak was interpreted to indicate 1974, synchronous with peak leaded gasoline usage in the United States. Three peaks in Mo concentrations in the guano core correspond to Mo concentration peaks in ice cores and date to 1975, 1980, and 1989. These peaks reflect increased Mo concentrations sourced from anthropogenic coal and oil combustion. Our novel method utilizing heavy metals suggests that heavy metal peaks are an effective method for dating modern guano deposits, opening new opportunities for linking guano-based paleoenvironmental research with modern observations.