Dalva M, Moore T R, Kalacska M, Leblanc G
Department of Geography, McGill University, 805 Sherbrooke St. W., Montreal, QC H3A 0B9, Canada.
National Research Council of Canada, Flight Research Laboratory, 1920 Research Rd., Ottawa, ON K1A 0R6, Canada.
Forensic Sci Int. 2017 Aug;277:229-240. doi: 10.1016/j.forsciint.2017.05.013. Epub 2017 Jun 16.
The objective of the three-year study was to examine spatial and temporal patterns of fluxes and soil pore air concentrations of methane (CH), carbon dioxide (CO) and nitrous oxide (NO) from an experimental mass grave located in a temperate environment. The mass grave (5×10m) contained twenty pig carcasses at a depth of approximately 1m was compared to a plot of the same dimensions containing only disturbed soil, as well as an undisturbed plot. Soil pore air CH concentrations were sub-ambient (<1.8ppm) except at 75 and 100cm depths at the mass grave in years 1 and 2 but decreased in year 3. The consumption of CH within the aerobic soil resulted in small negative fluxes at the soil surface. Soil pore air CO concentration showed an increase with depth in all three plots, with the largest increase (>100,000ppm at 1m) in the mass grave, though there was a marked decrease from years 1 to 3. Surface fluxes of CO showed strong seasonal variations, peaking in summer. Soil pore air NO concentration showed major increases in the mass grave, compared to the other two plots with the pattern maintained over the three years, resulting in larger surface fluxes of NO. To establish the role of the carcasses in NO dynamics, we incubated a soil sample containing carcass material which resulted in fast rates of NO production and consumption. The maintenance of elevated pore air concentration and surface flux of NO throughout the 3 years suggests that this is a long-term pattern and likely the best of the three gases to use to detect graves. Thus, we suggest that measurement of soil pore air concentrations, especially of NO, could be a simple and effective approach to help determine the location of clandestine graves.
这项为期三年的研究旨在考察位于温带环境中的一个实验性乱葬岗甲烷（CH₄）、二氧化碳（CO₂）和一氧化二氮（N₂O）通量及土壤孔隙空气浓度的时空模式。该乱葬岗（5×10米）在约1米深处掩埋了20具猪尸体，将其与一块尺寸相同、仅含扰动土壤的地块以及一块未扰动地块进行比较。除了在第1年和第2年乱葬岗75厘米和100厘米深度处，土壤孔隙空气CH₄浓度低于环境水平（<1.8ppm），但在第3年有所下降。需氧土壤中CH₄的消耗导致土壤表面出现小的负通量。在所有三个地块中，土壤孔隙空气CO₂浓度均随深度增加，在乱葬岗中增加幅度最大（在1米深处>100,000ppm），不过从第1年到第3年有显著下降。CO₂的表面通量呈现出强烈的季节性变化，在夏季达到峰值。与其他两个地块相比，乱葬岗中土壤孔隙空气N₂O浓度大幅增加，且这种模式在三年中保持不变，导致N₂O的表面通量更大。为确定尸体在N₂O动态中的作用，我们对一份含有尸体物质的土壤样本进行了培养，结果显示N₂O的产生和消耗速率很快。在整个三年中，孔隙空气浓度和N₂O表面通量持续升高，这表明这是一种长期模式，并且可能是三种气体中最适合用于探测坟墓的。因此，我们建议测量土壤孔隙空气浓度，尤其是N₂O的浓度，可能是一种简单有效的方法，有助于确定秘密坟墓的位置。
