Disinfection byproduct formation potentials of wetlands, agricultural drains, and rivers and the effect of biodegradation on trihalomethane precursors.

Trihalomethane (THM) precursors are a significant problem in the San Joaquin River (SJR) watershed, an important source of drinking water for >20 million people. Trihalomethane precursors diminish drinking water quality and are formed during natural decomposition of organic matter in aquatic systems. This study sought to identify sources of chlorine-reactive dissolved organic carbon (DOC) in the SJR watershed and to determine if wetlands were more important sources of THM precursors than nearby rivers and agricultural drains. The effects of biodegradation on DOC quality and quantity were investigated and analyzed across drainage type. Results show wetland drainage contained comparable bromide concentrations and organic carbon aromaticity but contained more than two times the average DOC concentrations found in agricultural drains and rivers. Wetland DOC did not have an increased propensity to form THMs when compared with the other drainage types, despite significantly higher wetland formation potentials. The higher formation potentials measured in wetland drainages were attributed to higher DOC concentrations; the positive correlation found between DOC and trihalomethane formation potentials (THMFPs) and the significantly higher wetland DOC concentrations suggest that increased wetland restoration could result in increased THMFPs in the SJR watershed. Wetland THM precursors were more resistant to biodegradation than THM precursors from agricultural and river samples. Results suggest that THM precursors in the SJR were from algae and were biodegraded.