A study of fecal coliform sources at a coastal site using colored dissolved organic matter (CDOM) as a water source tracer

摘要

Optical properties of colored dissolved organic matter (CDOM) were measured as a tracer of polluted waters in a Southern California surf-zone with consistently high levels of fecal indicator bacteria. Salinity, temperature, fecal coliform, absorbance (200-700 nm) and fluorescence (λ_(excitation) = 350 nm; λ_(emission) = 360-650 nm) were measured in the creek and surf-zone during a dry and rain event. Fluorescence to absorption ratios for CDOM were used to distinguish water masses, with two distinct CDOM end-members identified as creek (flu/abs = 8.7 +- 0.8 x 10~4) and coastal (flu/abs = 2.2 +- 0.3 × 10~4). Waters containing the same CDOM end-member had highly variable bacterial levels during the dry event, suggesting intermittent sources of bacteria added to a uniform water source, consistent with marine birds. During the rain event, increased levels of the creek end-member and bacteria indicated a second bacteria source from runoff.