Season matters: Timing of cadaver deposition influences soil biogeochemical changes in a temperate human taphonomic facility

Human taphonomic facilities (HTF) are outdoor spaces dedicated to research, educational and training activities related to human decomposition. Through the purging of decomposition by-products, a body within a HTF will generate a chemically and microbially disrupted zone of soil known as a Cadaver Decomposition Island (CDI). The biochemical dynamics of CDIs have been minimally investigated across contrasting seasons, thereby impeding our understanding of how cadaveric inputs are processed within temperate soils. This gap was addressed in a Canadian HTF by examining soil organic matter (SOM) chemistry and bacterial metabolic responses within the CDIs of donors bodies who were deposited under warm or cold seasonal conditions. Decomposition generated a pulse of SOM that was first rich in carbon then nitrogen. This was associated with an enrichment in δ¹³C and δ¹⁵N that was attributable to cadaveric tissues and enhanced mineralization. Fluorescence spectroscopy also revealed a transition in the molecular characteristics of organic matter that was indicative of a shift from recalcitrant terrestrial substances to labile microbial compounds. In addition, bacteria were observed to preferentially utilize carbohydrate substrates for energy production. These effects arose during the Active-Dry phases of decomposition, occurring between 13-139 days for warm deposited donors, but were delayed (31-364 days) and reduced in magnitude for cold donors. All changes were limited to the A-horizon and within a sampling radius of 20 cm from the body. These findings will inform temperate HTFs of their potential environmental impact and direct the development of soil-based forensic techniques.