Seasonal Variation of Disinfection Byproduct Precursors in a Large Water Supply

Disinfection byproduct (DBP) precursors originate in large reservoirs from at least three types of sources: (1) watershed or allochthonous, (2) algal or autochthonous, and (3) bottom sediments or benthic. The properties of the bulk natural organic matter (NOM) and the DBP precursor content of that NOM are unique to each source. Knowledge about the relative importance of these three sources would be valuable in understanding the natural variability in DBP precursor occurrence and in managing source waters for the purpose of minimizing DBP precursors. In this study, we used temporal and spatial water quality data from a drinking water reservoir to shed light on autochthonous and benthic sources of NOM and DBP precursors. The Cannonsville Reservoir (New York) was chosen for this work because of its well‐documented water quality. To assist in the data analysis, we developed a series of two‐dimensional contour plots that bring clarity to benthic and near‐surface (algal) processes on water quality. Combining conventional water quality parameters with DBP precursor analysis can facilitate a more comprehensive understanding of limnological factors that define DBP precursor levels. These data were compared with known properties of NOM and related natural biochemical parameters. From this analysis, we conclude that algal‐dominated NOM contributes disproportionately to dihaloacetonitrile formation, whereas watershed‐dominated NOM is especially rich in trihaloacetic acid and trihalomethane precursors as well as ultraviolet‐absorbing substances. The sediment‐dominated precursor behaved like a mix of the other two but most resembled the watershed NOM.