The decomposition of vertebrate carcasses in terrestrial environments produces dynamic biogeochemical hotspots in the soil, resulting in rapid and persisting changes in soil chemistry and biology. The nematode communities in these hotspots have been shown to change; however, existing studies lack the resolution to clearly reveal successional trajectories of these communities. In addition, there is interest in the forensic science community in understanding fine-scale biological succession patterns under decomposing humans to better inform time-since-death predictions. The objective of our study was to perform a high-resolution, long-term assessment of soil nematode succession beneath decomposing human bodies and correlate these results to soil chemistry to identify successional patterns and indicator taxa specific to discrete time points associated with decomposition progression. Three donated human subjects, 90.7-91.6 kg each, were placed at the UT Anthropology Research Facility in direct contact with soil and allowed to decompose naturally for one year. Soil sampling consisted of composited 15-cm cores from beneath donors at regular intervals (350ADD). Nematodes were extracted by sugar centrifugation-flotation, and analyzed to family and genus level by microscopy for abundance and community analysis. Soil pH, electrical conductivity, dissolved oxygen, and ammonium were measured at each sampling time point.
Results/Conclusions
The onset of active decay (day 8) and introduction of decomposition fluids into the soils resulted in a decrease in soil pH and dissolved oxygen (DO), accompanied by elevated electrical conductivity (EC), ammonium (NH4+) and CO2. While DO returned to normal levels later (day 168), pH and EC remained elevated for the duration of the study. Nematode abundances, richness, and diversity decreased during active decay (day 8) and this effect persisted through the early stages of advanced decay (day 58), at which point abundances sharply increased and successional patterns emerged. Communities present after day 58 were dominated by a sequence of bacterial feeding enrichment opportunists (Rhabditidae, Diploscapter, and Diplogasteridae) and fungal feeding Aphelenchoides. By late advanced decay (day 117) nematode richness and diversity increased, and taxa associated with stable soil conditions returned (e.g. bacterial feeder Acrobeloides). Notably, Filenchus, commonly found in control soils nearby, dropped below detectable limits in decomposition-impacted soils and remained suppressed throughout the remainder of the study. After one year, both soil chemistry parameters and nematode community membership were still significantly altered. Our study has revealed successional patterns associated with human decomposition that may hold promise for forensic science applications.