 |
| Titel |
Sources and accumulation of organic carbon in the Pearl River Estuary surface sediment as indicated by elemental, stable carbon isotopic, and carbohydrate compositions |
| VerfasserIn |
B. He, M. Dai, W. Huang, Q. Liu, H. Chen, L. Xu |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1726-4170
|
| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 7, no. 10 ; Nr. 7, no. 10 (2010-10-28), S.3343-3362 |
| Datensatznummer |
250005028
|
| Publikation (Nr.) |
 copernicus.org/bg-7-3343-2010.pdf |
|
|
|
|
|
| Zusammenfassung |
| Organic matter in surface sediments from the upper reach of the Pearl River
Estuary and Lingdingyang Bay, as well as the adjacent northern South China
Sea shelf was characterized using a variety of techniques, including
elemental (C and N) ratio, bulk stable organic carbon isotopic composition
(δ13C), and carbohydrate composition analyses. Total organic
carbon (TOC) content was 1.21±0.45% in the upper reach, down to
1.00±0.22% in Lingdingyang Bay and to 0.80±0.10% on the
inner shelf and 0.58±0.06% on the outer shelf. δ13C
values ranged from −25.1‰ to −21.3‰ in Lingdingyang Bay and the South
China Sea shelf, with a trend of enrichment seawards. The spatial trend in
C/N ratios mirrored that of δ13C, with a substantial decrease
in C/N ratio offshore. Total carbohydrate yields ranged from 22.1 to 26.7 mg
(100 mg OC)−1, and typically followed TOC concentrations in the
estuarine and shelf sediments. Total neutral sugars, as detected by the nine
major monosaccharides (lyxose, rhamnose, ribose, arabinose, fucose, xylose,
galactose, mannose, and glucose), were between 4.0 and 18.6 mg (100 mg
OC)−1 in the same sediments, suggesting that significant amounts of
carbohydrates were not neutral aldoses. Using a two end-member mixing model
based on δ13C values and C/N ratios, we estimated that the terrestrial
organic carbon contribution to the surface sediment TOC was ca. 78±11% for
Lingdingyang Bay, 34±4% for the inner shelf, and 5.5±1% for the outer shelf. The molecular composition of the carbohydrate in
the surface sediments also suggested that the inner estuary was rich in
terrestrially derived carbohydrates but that their contribution decreased
offshore. A relatively high abundance of deoxyhexoses in the estuary and
shelf indicated a considerable bacterial source of these carbohydrates,
implying that sediment organic matter had undergone extensive degradation
and/or transformation during transport. Sediment budget based on calculated
regional accumulation rates showed that only ~50% of the influxes
of terrestrial organic carbon were accumulated in the estuary. This
relatively low accumulation efficiency of terrestrial organic matter as
compared to the total suspended solids (accumulation efficiency ~73%)
suggested significant degradation of the terrestrial organic carbon
within the estuarine system after its discharge from the river. This study
demonstrated that the combination of the bulk organic matter properties
together with the isotopic composition and molecular-level carbohydrate
compositions can be an efficient way to track down the source and fate of
organic matter in highly dynamic estuarine and coastal systems. The
predominance of terrestrially originated organic matter in the sediment and
its generally low accumulation efficiency within the estuary is not
surprising, and yet it may have important implications in light of the heavy
anthropogenic discharges into the Pearl River Estuary during the past thirty
years. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|