Natural organic matter and their binding to iron (iii) hydr(oxides) as studied by fluorescence spectroscopy and flow adsorption microcalorimetry

Abstract

Organic matter (OM) is complex with controlling roles in global carbon, nutrient and contaminant cycling. The first part of this study combines 2D- (2D-PCFS) and time-resolved fluorescence spectroscopy in characterizing OM from fire- and non-fire-processed sources. Fire- and non-fire-processed OM produced 2D-PCFS spectra that were respectively, blue- and red-shifted compared to their unprocessed counterparts. Blue shift increased with burn temperature which was positively correlated to intensity-weighted lifetime of water-extracted OM components. The lifetime-temperature relationship was used to predict fire temperatures at tree- and field-scales. The second part of this study combines energetics data from flow adsorption microcalorimetry (FAMC) with 2D-PCFS and UV-vis spectroscopy to assess sorptive characteristics of fire- versus non-fire-processed OM on ferrihydrite. Energetics and kinetics data showed that OM-ferrihydrite interactions had both endothermic and exothermic steps with rates that were pH dependent and inversely related to the energy of reaction. No evidence of ferrihydrite-induced OM changes were observed.