Improvement of oxygen transport functions in grave soils due to quicklime application depending on soil texture

Abstract

Quickliming (application of CaO) was tested as structure amelioration method in order to improve aeration properties in grave soils and thereby prevent decomposition problems due to an insufficient oxygen supply in the burial environment. CaO is expected to promote a stronger aggregation and stabilization in the backfilled soil and thereby enhance pore functionality. In this study, grave simulations (without buried corpses) were set up at three differently textured sites in Germany (S1: sandy loam, S2: silt loam, S3: clay loam texture) with clay contents ranging from 6 to 35%. Each site included two grave simulations: (i) excavation and backfill only (“Nil” treatment) and (ii) addition of 20 kg CaO m−3 to the soil backfill (“CaO” treatment) prior to backfilling. Undisturbed soil cores were repeatedly taken at specific time intervals to determine the aeration status in the simulated cover layer (L1, above potential coffin position in 50 cm depth) and the coffin layer (L2, 90–135 cm depth) by measuring the diffusivity and pore functionality parameters (air-filled porosity (θa), pore continuity index (C1) and tortuosity (Τ)) at field capacity (−6 kPa). Field measurements included a continuous monitoring of field moisture conditions (matric potential) and repeated measurements (2–4 week intervals) of O2 concentrations in both layers (L1 and L2).The addition of CaO to the backfill improved the aeration properties in the grave simulations; this was indicated by a higher diffusivity and mostly higher O2 concentrations at all sites, which was related to a more continuous (C1) and less tortuous (Τ) pore system compared to the “Nil” treatment. However, under field conditions, the effectiveness of soil-lime-mixtures was reduced with increasing clay and soil moisture content. A permanently high water saturation in L2 at S2 and S3 offsets the positive effects of CaO on gas transport ability and therefore restricts an undisturbed gas exchange from the atmosphere to the coffin layer. Consequently, for grave soils with high stagnic/ground water level an additional drainage is needed, while for cohesive, clay-enriched soils a more pronounced homogenization and lime mixing intensity is recommended.