Calorimetric Studies of Carbon Pool Dynamics and Organic Matter Stability In Biogeochemical Materials.

Differential scanning calorimetry and thermogravimetry (DSC-TG) can be used to determine stability of organics in a range of biogeochemical samples.  Qualitative information from the thermograms (such as peak shape and relative intensities of each peak) allow for comparisons between samples and treatments.  More useful, however, are the quantitative measures available: peak heights of endothermic and exothermic transformations, ash content, sequential mass loss steps, and enthalpy determinations of individual transformations. 

Second derivatives of thermal traces identify fine differences between sample treatments such as chemical or physical separation, composition of organic fractions, stages of ecosystem soil development and changes in soils as influenced by different vegetation types on a common soil.  Analysis of DOC and coniferous forest soils under varying understory control management treatments show patterns of varying soil organic carbon stability. 

Currently two key exothermic reactions due to organic matter have been repeatedly measured in soil materials: a low temperature region (~350°C) associated with nominally ‘labile’ aliphatic compounds and lower molecular weight fragments and a higher temperature region (~550°C) associated with nominally ‘recalcitrant’ aromatic compounds and mineral stabilized C.  Working with municipal yard waste composts, whole soils, and flocs of metal coagulants with wetland-derived DOC, we are working to characterize enthalpic values of major reactions and develop relationships with other chemical properties (organic C content, C/N values, δ¹³C values, etc.).

Custom blends of composts will be created using various known plant materials that were labeled with stable C and/or N before the plants were harvested.  Uniquely labeled plant types or components will allow for element tracking during composting. 

Recent work has focused on utilizing the DSC as a separation method by coupling the it with an isotope ratio mass spectrometer for real time evolved gas analysis in order to correlate the enthalpy of each thermal degradation reaction (or “compound class”) with its unique δ¹³C signature.  Along with C mass data, this combination of information will facilitate greater understanding of the C cycle based on energetic inputs (chemical energy from photosynthesis) and C stabilization and associated chemical bond energy based on units that easily cross ecosystem boundaries (Joules).