25th International Meeting on Organic Geochemistry IMOG 2011

P-515
Variability of terrestrially-derived particulate organic carbon in
the lower Yangtze River (Changjiang): A monsoon dominated
water system
Ying Wu, Hao Yu, Jing Zhang, ZhuoYi Zhu
State Key Laboratory of Estuarine and Coastal Research, Shanghai, China (corresponding
author:wuying@sklec.ecnu.edu.cn)
As human impacts on the environment increase,
rivers and coastal systems are becoming more
vulnerable through enhanced fertilizer usage,
damming, deforestation and other land-use changes.
Additionally, phenomena associated with climate
change, such as the increase frequency of ENSO or
extreme climate events, have resulted in changes in
riverine runoff and sediment load. Both changes will
certainly impact the flux and composition of materials
from the rivers to the ocean.
Particulate organic matter from the lower reach of the
Yangtze River was collected monthly from 2003
through 2006. The samples were then examined
using elemental (%OC, C/N), carbon isotopic and
terrigenous biomarker analyses. The composition of
lignin phenols exhibited distinguishable seasonal
variation. The seasonal variation in various
parameters was found to be larger than the
interannual variability in the lower Yangtze River,
which is dominated by a monsoon climate.
Additionally, the mass-normalized lignin yields were
negatively correlated with the water discharge.
Furthermore, the S/V and C/V ratios of the samples
indicated that both woody and non-woody angiosperm
plant detritus were the primary sources of lignin
phenols. Moreover, the (Ad/Al)v ratios revealed that
most SPM samples were relatively fresh, although
more degradation was observed in 2006. A three-endmember
model was built with plant detritus, soils and
phytoplankton as three sources of organic matter in
SPM and the results showed that the soil was the
dominant contributor of organic matter to the SPM.
Although variability in the lignin composition of
particulate organic matter is related to the sources, it
can also be attributed to other factors. Climate
change could be a large driving force in alteration of
the flux of terrestrial-derived organic matter. A good
correlation between the Nino 3.4 Index and sediment
load & �8 was observed from 2003 to 2006,
especially when a 2 months lag was considered.
However, during 2006, the precipitation was also
impacted by global warming, which resulted in
extreme drought over the drainage basin. Moreover,
reservoir impoundment resulted in a longer retention
time for terrigenous organic matter. Additionally,
elevated Chl-a concentrations were observed as the
SPM decreased. These findings indicate that a
decrease in sediment load will not only result in
altered particulate organic matter concentrations, but
also in changes in the structure of organic material.
These changes will result in more fresh and labile
organic material being transported into coastal
systems, which will have an important impact on the
regional carbon cycle and marine ecosystem.
However, these findings are based on continuous
observations from one lower reach station. In the
future, data from more sampling stations located at
different distances from the Estuary should be
considered to gain a better understanding of the
biogeochemistry of terrestrial-derived organic matter
in the Yangtze River.
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