LOSS-ON-IGNITION (LOI) IN HOLOCENE FLUVIAL SEDIMENTS: THE INFLUENCE OF PARTICLE-SIZE VARIABILITY

Loss-on-ignition is a low cost and commonly used method for estimating organic carbon content, but can be strongly influenced by other physical and chemical properties of the sediment. A 480 cm column of fluvial sediments near the confluence of the South Saluda and Oolenoy rivers in Pickens County, South Carolina was examined to determine what factors contribute to LOI values. Three buried A horizons were apparent in field observations between the surface horizon and a depth of 285 centimeters, based on darker colors (lower value and chroma) and coarser textures. The darker color of the Ab horizons suggests higher organic carbon content within these horizons. Sediment textures of the horizons sampled vary from coarse sand to clay. Loss on ignition was conducted on the samples by measuring the dry weight after heating at 110°F, then ignition at 430°C for approximately 18 hours before measuring the post-ignition weight. LOI values range from 0.9 to 7.2% with highest values in clayey strata and lowest values in sands. For these sediments there is a positive correlation between LOI and clay content. An exception is the modern A horizon which has a relatively high LOI of 3.8% despite its sandy texture. Thus buried A horizons are not necessarily represented by peaks in LOI, owing to the coarser textures of these horizons. Measurements of particle size distribution along with accurate organic carbon measures can be used to determine a factor for converting LOI to organic carbon for this and similar geomorphic settings.