25th International Meeting on Organic Geochemistry IMOG 2011

P-226
Seasonal variations and characters of terrestrial particulate
organic matter in exterior rivers in Southeast China: inferred
from bulk properties and lignin phenols
Hongyan Bao, Ying Wu
State Key Laboratory of Estuarine and Coastal research, Shanghai, China (corresponding
author:baohy.ecnu@gmail.com)
Exterior rivers can significantly influence the
biogeochemical processes of the coastal area. East
China Sea accepts suspended sediment derived from
Yangtze River and Zhejiang Mountainous Rivers.
Though the sediment load of Zhejiang small rivers is
only 6% of the Yangtze river, but since the southeast
China is under the impact of subtropical monsoon,
water discharge during extreme events could be more
than 40 times of averaged water discharge,
sometimes 1000 times (Li et al., 2009; Yu, 2009),
those small rivers might transport significant
suspended particles during extreme event (Hilton,
2008). Previous studies regarding the terrestrial
organic carbon buried in East China Sea mainly
focused on Yangtze river (Zhu et al., 2008), studies
concerning those small mountainous rivers are
seldom. Here we present a study focuses on the
characters and seasonal variations of terrestrial
organic matter in Zhejiang mountainous river, and
compare to Yangtze river, find out the potential role of
these rivers in transporting terrestrial organic carbon.
Suspended particles of 7 rivers were sampled in
rainy season and dry season, respectively. The
elevation of these 7 rivers ranged from 500m to
1200m, with a drainage basin area varied from
1500km 2 to 55600km 2 . Bulk properties (POC% and
δ 13 C) and lignin phenols were analysed. POC%
showed higher variation in the rainy season than in
dry season, averaged at 2.0±1.6% and 1.0± 0.2% in
rainy season and dry season, respectively. Lignin
phenol concentrations (Σ8) ranged from 0.7 to
3.9mg/10g dw in the rainy season and 0.5 to
3.6mg/10g dw in the dry season. S/V and C/V ratio
suggested that terrestrial OM mainly came from the
mixture of angiosperm nonwoody and woody tissues,
in some rivers, e.g. Qiantang river, a significant
proportion was derived from woody tissues. The bulk
properties and lignin phenols signals of Qiantang river
are significantly different to that of other mountainous
rivers. This might caused by its relatively larger
drainage basin area (55600km 2 ) and lower
elevation/length ratio, so we exclude this river from
statistics analysis.
Statistics analysis indicated that though bulk
properties showed no differences between rainy
season and dry season, lignin phenol concentration
(Σ8) and degradation parameter ((Ad/Al)v) showed
significant differences between two seasons.
Generally, compared to dry season, in rainy season,
the particles contains more fresh terrestrial OM
(higher Σ8 and lower (Ad/Al)v ratio), which suggest
that during flood season, more fresh plant debris or
newly formed soils were rushed out from the drainage
basin. Compare to Yangtze river, in the rainy season,
bulk properties of these small rivers were close to that
of Yangtze river, but with a higher (Ad/Al)v ratio,
which inferred that during rainy season, small
mountainous river contains more soil derived OM than
Yangtze river; in the dry season, bulk properties and
lignin phenols all showed significant differences to
that of Yangtze river, with lower POC% and lower
terrestrial OM. The differences in chemical properties
between Yangtze river and Zhejiang river sediments
in different seasons may provide a way to quantify the
source of sedimentary organic carbon preserved in
the coastal region.
References
Li, B. G., Wang, C. H., Zhou, H. Q., Wu, X. Y.
and Yang, H., 2009. Adjustment mechanism on the
erosion and accretion of riverbed in the Jiaojiang
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