Tracing terrestrial versus marine sources of dissolved organic carbon in a coastal bay using stable carbon isotopes

The sources of dissolved organic matter (DOM) in coastal waters are diverse, and they play different roles in the biogeochemistry and ecosystems of the ocean. In this study, we measured dissolved organic carbon (DOC) and nitrogen (DON), the stable carbon isotopic composition of dissolved organic car...

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Bibliographic Details
Published in:Biogeosciences 2020-01, Vol.17 (1), p.135-144
Main Authors: Lee, Shin-Ah, Kim, Tae-Hoon, Kim, Guebuem
Format: Article
Language:English
Subjects:
Bay water
Biogeochemistry
Carbon
Carbon isotopes
Carbon sources
Carbon-nitrogen ratio
Chemical analysis
Cities and towns
Coastal waters
Dissolved organic carbon
Dissolved organic matter
Ecosystems
Fluorescence
Isotope composition
Isotopes
Marine ecosystems
Nitrogen
Organic carbon
Organic matter
Plants (Organisms)
Salinity
Salinity effects
Seawater
Terrestrial environments
Tracers
Water analysis
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Summary:The sources of dissolved organic matter (DOM) in coastal waters are diverse, and they play different roles in the biogeochemistry and ecosystems of the ocean. In this study, we measured dissolved organic carbon (DOC) and nitrogen (DON), the stable carbon isotopic composition of dissolved organic carbon (δ13C-DOC), and fluorescent dissolved organic matter (FDOM) in coastal bay waters surrounded by large cities (Masan Bay, Republic of Korea) to determine the different DOM sources in this region. The surface seawater samples were collected in two sampling campaigns (August 2011 and August 2016). The salinities were in the range of 10–21 in 2011 and 25–32 in 2016. In 2011, excess DOC was observed in high-salinity (16–21) waters; the excess DOC source was found to be mainly from marine autochthonous production according to the δ13C-DOC values (−23.7 ‰ to −20.6 ‰), the higher concentrations of protein-like FDOM, and the lower DOC∕DON (C∕N) ratios (8–15). In contrast, excess DOC observed in high-salinity waters in 2016 was characterized by low FDOM, more depleted δ13C values (−28.8 ‰ to −21.1 ‰), and high C∕N ratios (13–45), suggesting that the source of excess DOC is terrestrial C3 plants by direct land–seawater interactions. Our results show that multiple DOM tracers such as δ13C-DOC, FDOM, and C∕N ratios are powerful for determining different sources of DOM occurring in coastal waters.
ISSN:1726-4189
1726-4170
1726-4189
DOI:10.5194/bg-17-135-2020