Origin and transport of sedimentary organic matter in the Yalujiang estuary,North China |
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| Authors: | Email author" target="_blank">Ying?WuEmail author Jing?Zhang Ki?Woong?Cho Gi?Hoon?Hong Chang?Soo?Chung |
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| Institution: | (1) Environmental Geochemistry Laboratory, Southeast Environmental Research Center (SERC) and Department of Chemistry & Biochemistry, Florida International University, Miami, FL 33199, USA;(2) Department of Marine & Atmospheric Chemistry, Rosenstiel School of Marine & Atmospheric Science, Rickenbacker Causeway, Miami, FL 33149, USA; |
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| Abstract: | The biogeochemistry of organic matter (OM) in a macrotidal estuary, the Yalujiang River, was studied during two cruises: the
flood season in August 1994 and the dry season in April 1996. Surface sediments were collected in the riverine zone (RZ),
the turbidity maximum zone (TMZ), and the marine zone (MZ). The molecular distribution of the n-alkanes and fatty acid series
and bulk sediment characteristics, such as C:N and δ13C, were used to assess differences in OM source and transport from the river upstream to the marine end member. Higher C:N
values typical for terrestrial sources were observed at the upper reach for both seasons. The δ13C of OM in surface sediments varied from −27.3‰ to −21.6‰ in the flood season and from −26.8‰ to −31‰ in the dry season. The
concentrations of n-alkanes varied between 0.3–21.4 μg g−1 and the variation of fatty acids was 4.8–32.9 μg g−1. The data showed mixing of terrestrial and autochthonous OM in the middle and lower reaches. The distribution of lipids (n-alkanes
and Carbon Preference Index) encountered in this study confirmed the importance of terrestrial OM in the sediment samples
from degraded soil material. The distribution of fatty acids suggested important phytoplankton, zooplankton, and microbial
signals (short-chain and unsaturated acids; ≤C20). Branched fatty acids, such as the iso- and anteiso-C15 and C17 compounds, relfect bacterial contributions. All samples were characterized by a high proportion of mixture inputs in both
seasons. A slight decreasing trend was observed with increasing salinity except for the highest percentage of mixed fatty
acids in the TMZ of the flood season. Terrestrial fatty acids were approximately 20% in the flood season and 27–46% in the
dry season. Differences in hydrological conditions and primary production between the TMZ, RZ, and MZ resulted in different
OM distributions, which are reflected in the sources and degree of diagenesis of the sedimentary OM. Seasonal variation may
be strongly influenced by hydrological characteristics rather than primary productivity and anthropogenic activities in the
Yalujiang region. |
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