posted on 2007-11-15, 00:00authored byAlex T. Chow, Randy A. Dahlgren, John A. Harrison
High levels of dissolved organic carbon (DOC) and
bromide (Br) in the Sacramento and San Joaquin River
waterways are of concern because DOC and Br are organic
and inorganic precursors, respectively, of carcinogenic
and mutagenic disinfection byproducts (DBPs). The
Sacramento and San Joaquin Rivers are the two major
rivers supplying water to the San Francisco Bay Delta, but
sources and loads of DBP precursors into the Delta are
still uncertain. The major objectives of this study were to
evaluate both the quantity (DOC and Br fluxes) and the
quality (reactivity in forming DBPs) of DBP precursors from
the Sacramento and San Joaquin watersheds. Water
samples were collected every 2 weeks at up to 35 locations
along the Sacramento and San Joaquin Rivers and
selected tributaries and analyzed for DOC (4 years), Br (1
year), and ultraviolet absorbance at 254 nm (1 year).
Selected water samples were also tested for THM formation
potential. Estimated fluxes for the Sacramento River
were 39 000 ± 12 000 Mg DOC year-1 and 59 Mg of Br
year-1 as compared to 9000 ± 5000 Mg of DOC year-1 and
1302 Mg of Br year-1 for the San Joaquin River. The
THM formation potential was higher in the San Joaquin
River (441 ± 49 μg L-1) than the Sacramento River (176 ±
20 μg L-1) because of higher concentrations of both
organic (DOC = 3.62 ± 0.14 vs 1.92 ± 0.09 mg L-1) and
inorganic DBP (Br = 0.80 ± 0.07 vs <0.03 ± 0.01 mg L-1)
precursors. The Sacramento River's greater DOC load
despite lower DOC concentrations is due to its discharge
being about 5 times greater than the San Joaquin River
(50 × 109 vs 10 × 109 L day-1). The DOC concentration was
significantly correlated with several land-cover types,
including agriculture; however, no relationship was found
between DOC quality and land-cover at the watershed
scale.