posted on 2019-05-29, 00:00authored byHuan Chen, Kuo-Pei Tsai, Qiong Su, Alex T. Chow, Jun-Jian Wang
More than half of the drinking water
supply in the United States
originates from forest watersheds, where terrestrial dissolved organic
matter (DOM) is known as an important disinfection byproduct (DBP)
precursor. Throughfall-derived DOM, a significant portion of terrestrial
DOM, has seldom been evaluated for its formation potential of DBPs.
Here, we collected throughfall and leaf extracts of an evergreen (loblolly
pine, Pinus taeda L.) and a deciduous tree species
(turkey oak, Quercus cerris L.) in South Carolina
to explore their seasonal DOM quantity, optical properties, and DBP
formation potential. Elevated dissolved organic carbon (DOC) from
rainwater (1.2 ± 0.4 mg/L) to pine (26.0 ± 19.7 mg/L) and oak throughfall (38.8 ±
37.8 mg/L) indicated canopy can be a significant DOM source. DOM aromaticity
(indicated by specific ultraviolet absorbance at 254 nm) was higher
in oak than pine throughfall and higher in throughfall than leaf extracts.
The throughfall DOM characteristics were seasonally more stable for
the evergreen pine than for the deciduous oak. The specific DBP formation
potential of pine and oak throughfall both varied greatly across seasons,
with values of 52.7 ± 17.3 and 58.6 ± 15.1 μg/g-DOC
for trihalomethanes, 0.82 ± 0.35 and 0.64 ± 0.11 μg/g-DOC
for haloacetonitriles, 0.59 ± 0.60 and 0.22 ± 0.05 μg/g-DOC
for haloketones, and 4.51 ± 2.25 and 4.20 ± 2.76 μg/g-DOC
for chloral hydrate, respectively. We estimated the contribution of
canopies on runoff DOC yield, and results suggested that the highest
contribution would occur in the fall season. Results suggest that
throughfall DOM is an important and overlooked terrestrial DBP precursor,
and its seasonal variation is forest-type-dependent.