Geospatial Variability of Fluorescent Dissolved Organic Matter in Urban Watersheds: Relationships with Land Cover and Wastewater Infrastructure

We
investigated the fluorescent dissolved organic matter (FDOM)
composition in two watersheds with variable land cover and wastewater
infrastructure, including sanitary sewers and septic systems. A four-component
parallel factor analysis model was constructed from 295 excitation–emission
matrices recorded for stream samples to examine relationships between
FDOM and geospatial parameters. The contributions of humic acid- and
fulvic acid-like fluorescence components (e.g., C1, C2, C3) were fairly
consistent across a 12 month period for the 27 sampling sites. In
contrast, the protein-like fluorescence component (C4) and a related
ratiometric wastewater indicator (C4/C3) exhibited high variability
in urban tributaries, suggesting that some sites were impacted by
leaking sewer infrastructure. Principal component analysis indicated
that urban areas clustered with impervious surfaces and sanitary sewer
density, and cross-covariance analysis identified strong positive
correlations between C4, impervious surfaces, and sanitary sewer density
at short lag distances. The presence of wastewater was confirmed by
detection of sucralose (up to 1,660 ng L–1) and
caffeine (up to 1,740 ng L–1). Our findings not
only highlight the potential for C4 to serve as an indicator of nearby,
compromised sanitary sewer infrastructure, but also suggest that geospatial
data can be used to predict areas vulnerable to wastewater contamination.