SURFACE AND SUBSURFACE VERTEBRATE DECOMPOSITION RESULT IN PROTRACTED SOIL NITROGEN STABLE ISOTOPIC ENRICHMENT

Vertebrate decomposition results in dynamic changes to soil biogeochemistry on multiple spatial and temporal scales. As a consequence of decay, the input of carbon (C) and nitrogen (N) stimulates microbial nitrification and denitrification, and results in spatial changes to soil chemistry surrounding (~60 cm) and beneath (~10 cm) a carcass in surface systems. In addition, soils exhibit δ¹⁵N enrichment for up to at least 3 years in some ecosystems. Despite the recent work quantifying the impacts of vertebrate decay on surface soils, much less is known about subsurface, or burial, environments. Soils were collected from the surface and at three depths (30, 70, 75 cm) within a multi-individual grave 4 years after burial. Prior results revealed that there were biological (micro- and macro-fauna) and chemical signatures of decomposition at depth, indicating that decay can result in a long-lived disruption to soil biogeochemistry. At depth, soil δ¹⁵N composition was 12.2‰, which represents a 10‰ enrichment compared to surface soils and ~5‰ enrichment compared to control soils at depth, indicating that decay has the potential to impart a long-lived signature on soil stable isotopic composition. The presence of elevated ammonium, low nitrification potential rates, and elevated dissolved organic N four years postmortem suggests that anaerobic conditions in the subsurface will result in protracted N cycling compared to surface decay. Delayed nitrification and denitrification may result in much longer lived δ¹⁵N enrichment at depth, and may serve as a chemical marker of clandestine burials.