INCUBATIONS VS. FLUORESCENCE SPECTROSCOPY: A FIELD AND LAB STUDY ON DOM BIOAVAILABILITY

Carbon (C) bioavailability can be assessed by monitoring the decrease in organic C or the increase in CO₂ in lab incubations, an effective but laborious approach. Another way of assessing the characteristics of aqueous C is the use of fluorescence spectroscopy, a fast and reliable method to assess DOM in natural waters. Fluorescence data shows us the characteristics of a very complex mixture of organic, fluorescent molecules, some of which might be more bioavailable that others. Several projects investigated the use of fluorescence spectroscopy as indicator for bioavailability, however, several caveats exist, including the fact that bioavailability proxies might vary with DOM origin and fate. Variation in site specific proxies may include mineralogic composition (specifically the presence of Fe, Al, and Ca²⁺) of the soil, pH, vegetation present (and extent of vegetation coverage), and the soil sorption capacity.

Our research therefore uses a combined experimental and field approach to test for typical bioavailability proxies such as (X, Y, Z) and how they perform in predicting bioavailability verified with concurrent incubation studies. Several C sources are being used such as leaf litter leachate, aqueous soil extracts and stream waters and along with spectral methods microbial biomass, %respired C and microbial enzyme activity is assessed. Preliminary data suggests that respiration rates are similar amongst study sites depending on initial DOM concentration, but the fluorescence characteristics vary from site to site, specifically the driving components gathered from parallel factor analysis (PARAFAC).