Contribution of a Storm Event to Disinfection Byproduct Formation: Natural Organic Matter Sources, Characteristics, and Mobilization

This study investigates the relationship between storm-driven changes in natural organic matter (NOM) and disinfection byproduct (DBP) formation. The novel framework presented correlates specific differential absorbance at 254 nm (Sp-ΔUV 254 ), which measures the change in UV 254 due to chlorination normalized by initial dissolved organic carbon (DOC) concentration, with critical water quality parameters such as chlorine demand, DBP formation, size-fractionated NOM, and lignin to enhance mechanistic understandings of DBP precursor dynamics. To evaluate the impact of a storm on the DBP precursor dynamics, samples were collected from the Neversink River (NY) during a high-flow event. The formation of total trihalomethanes (THMs), or specific trihalomethanes (Sp-THM) when normalized by initial DOC, strongly correlated to Sp-ΔUV 254 . The pre- and postchlorinated samples’ quotients of absorbances at 250 and 365 nm ( E 2 / E 3 ) yielded a strong correlation despite a decreased ΔUV 254 due to chlorination, suggesting dissolved organic matter transformation to less aromatic structures, in agreement with size exclusion chromatography (SEC) data. A novel SEC-DOC technique showed THM precursors increased during the rising limb of the storm with a predominant molecular weight range of 2000–10,000 Da. Stable water isotope (δ 18 O) measurements suggest quick mobilization of stored NOM accumulated in the watershed, which was also supported by quantified lignin concentrations.