Reactivity of Triplet Excited States of Dissolved Natural Organic Matter in Stormflow from Mixed-Use Watersheds

Dissolved organic matter (DOM) quantity and composition control the rate of formation (R_f,T) of triplet excited states of dissolved natural organic matter (³DOM*) and the efficiency of ³DOM* formation (the apparent quantum yield, AQY_T). Here, the reactivity of ³DOM* in stormflow samples collected from watersheds with variable land covers is examined. Stormflow DOM reflects variability in DOM quantity and composition as a function of land cover and may be important in controlling the fate of cotransported pollutants. R_f,T and AQY_T were measured using 2,4,6-trimethylphenol in stormflow samples under simulated sunlight. The DOM source and composition was characterized using absorbance and fluorescence spectroscopies and high-resolution mass spectrometry. R_f,T and the total rate of light absorption by the water samples (R_a) increased with the dissolved organic carbon (DOC) concentration. AQY_T was independent of DOC concentration, but varied with DOM source: developed land cover (4-6%) ≈ open water > vegetated land cover (3%). AQY_T was positively related to an index for microbial/algal DOM content and negatively related to DOM molecular weight, DOM aromaticity, and the content of polyphenols. This work demonstrates that TMP is an effective probe for the determination of R_f,T and AQY_T in whole water samples after accounting for the inhibition of TMP photodegradation by DOM.