Chromophoric dissolved organic matter (CDOM) is an
important optically active substance in aquatic environments and plays a key
role in light attenuation and in the carbon, nitrogen and phosphorus
biogeochemical cycles. Although the optical properties, abundance, sources,
cycles, compositions and remote sensing estimations of CDOM have been widely
reported in different aquatic environments, little is known about the optical
properties and composition changes in CDOM along trophic gradients. Therefore,
we collected 821 samples from 22 lakes along a trophic gradient (oligotrophic to
eutrophic) in China from 2004 to 2015 and determined the CDOM spectral
absorption and nutrient concentrations. The total nitrogen (TN), total
phosphorus (TP), and
chlorophyll a (Chla)
concentrations and the Secchi disk depth (SDD) ranged from 0.02 to 24.75 mg/L,
0.002–3.471 mg/L, 0.03–882.66 μg/L, and 0.05–17.30 m,
respectively. The trophic state index (TSI) ranged from 1.55 to 98.91 and
covered different trophic states, from oligotrophic to hyper-eutrophic. The CDOM
absorption coefficient at 254 nm (a(254)) ranged from 1.68
to 92.65 m-1. Additionally, the CDOM sources and
composition parameters, including the spectral slope and relative molecular size
value, exhibited a substantial variability from the oligotrophic level to other
trophic levels. The natural logarithm value of the CDOM absorption,
lna(254), is highly linearly correlated with the TSI
(r2 = 0.92, p < .001, n = 821).
Oligotrophic lakes are distinguished
by a(254)<4 m−1,
and mesotrophic and eutrophic lakes are classified as
4 ≤ a(254)≤10
and a(254)>10 m−1,
respectively. The results suggested that the CDOM absorption
coefficient a(254) might be a more sensitive
single indicator of the trophic state than TN, TP,
Chla and SDD. Therefore, we proposed a CDOM
absorption coefficient and determined the threshold for defining the trophic
state of a lake. Several advantages of measuring and estimating CDOM, including
rapid experimental measurements, potential in situ optical sensor measurements
and large-spatial-scale remote sensing estimations, make it superior to
traditional TSI techniques for the rapid monitoring and assessment of lake
trophic states.
来源:Water
research 卷: 131 页: 255-263 出版年: 2017-Dec-26
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