Determining Amounts of Carbon Loss and Changes in  13 C Values From Soils Due To Biomass Burning Scott Werts Hope Jahren Department of Earth and Planetary Sciences Johns Hopkins University

Radiative Heating in Soil Profiles Limited attention paid to C org loss from soils during fires. –Discussions center around high organic soils (Histosols). Most soils contain several times the amount of carbon as the vegetation growing above it. Any soil can be affected by radiative heating during a fire. We chose soils at end members of pedogenic development in common landscapes.

Common Temperatures in Soil Beneath Fire Ranges from a few ˚C to over 700˚C –3 to 8˚C (Werts and Jahren, unpublished data) –700˚C in boreal ground fire (Ryan, 2002) Temperature increase highly dependent on moisture content of soil.

Field Temperature Data Record temperature of soil during fire –Every cm through 4 cm deep in soil

Camp Singewald Soil Temperatures Due To Fire

Camp Singewald Alfisol (older soil) Camp Singewald Inceptisol (younger soil)

Laboratory experiments Each horizon incinerated in Isotemp Muffle Furnace for 6 hours at temperatures ranging from 150 to 500˚C –Each have different amounts of organic carbon and clay content Pre and post-incineration carbon mass determined from elemental analyzer Pre and post-incineration  13 C values determined from mass spectrometer

Higher Temperatures Increase Carbon Loss Ratio

Combustion of Select Soil Components:

Similar  13 C Fractionation Patterns Among Soil Horizons

Above 100˚C, Carbon and Clay Content Have No Effect on C LR or  13 C Values

Carbon Loss From Soils Depths Over Time

Conclusions: Organic Carbon Losses Organic carbon is lost from the soil at temperatures as low as 150˚C. All measurable organic carbon is lost by 500˚C. The highest losses occur between 250 and 400˚C. –All soil horizons behaved in a similar manner regardless of original carbon or clay content.

Conclusions:  13 C values  13 C values increase in all horizons between 250 and 400˚ regardless of original carbon or clay content  13 C values below 250˚ may depend on the level of decomposition of the organic matter.

Future Directions: Further defining dynamics of  13 C changes due to increasing temperature. Apply experimental procedures to more soil types. Morphology changes of heated soils determined by SEM –Applications to paleosols