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 (Rf,T) of triplet excited states
of dissolved natural organic matter (3DOM*) and the efficiency
of 3DOM* formation (the apparent quantum
yield, AQYT). 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. Rf,T and AQYT 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. Rf,T and the total rate of light absorption by the water samples (Ra) increased with the dissolved organic carbon
(DOC) concentration. AQYT was independent of DOC concentration,
but varied with DOM source: developed land cover (4–6%) ≈
open water > vegetated land cover (3%). AQYT 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 Rf,T and AQYT in whole water samples after accounting for the inhibition
of TMP photodegradation by DOM.