THESIS
2022
1 online resource (88 pages) : illustrations (some color)
Abstract
Estuarine and coastal marine sediments are hot spot of carbon mineralization and oxygen
consumption. This thesis characterizes the sediment carbon and oxygen cycles in the Pearl
River Estuary (PRE) and the adjacent coastal shelf waters in the Northern South China Sea
(SCS). We collected sediments from 24 locations, measured the vertical distributions of
dissolved oxygen, dissolved inorganic carbon (DIC), particulate organic carbon (POC) and its
stable isotopes (δ
13C
POC), total nitrogen, along with physical characterization of the sediments
(i.e., porosity, density, and water contents). We quantified the fluxes of oxygen and DIC across
the sediment-water interface. Our results suggested that the sediments were strongly anoxic,
with oxygen penetrated from 1 to 7 mm into the sediments. The...[
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Estuarine and coastal marine sediments are hot spot of carbon mineralization and oxygen
consumption. This thesis characterizes the sediment carbon and oxygen cycles in the Pearl
River Estuary (PRE) and the adjacent coastal shelf waters in the Northern South China Sea
(SCS). We collected sediments from 24 locations, measured the vertical distributions of
dissolved oxygen, dissolved inorganic carbon (DIC), particulate organic carbon (POC) and its
stable isotopes (δ
13C
POC), total nitrogen, along with physical characterization of the sediments
(i.e., porosity, density, and water contents). We quantified the fluxes of oxygen and DIC across
the sediment-water interface. Our results suggested that the sediments were strongly anoxic,
with oxygen penetrated from 1 to 7 mm into the sediments. The total oxygen uptake (TOU)
ranged from 16.2 to 70.5 mmol m
-2 d
-1 (on average 41.5 mmol m
-2 d
-1), and dissolved oxygen
uptake (DOU) ranged from 1.7 to 20.4 mmol m
-2 d
-1 (on average 9.8 mmol m
-2 d
-1). Diffusive
fluxes of DIC ranged from 3.4 to 35.8 mmol m
-2 d
-1 (on average 15.8 mmol m
-2 d
-1). The lower
diffusive fluxes of oxygen and DIC compared to TOU suggest strong bioturbation in the
sediments. The sediments were derived from a mixture of marine and terrestrial sources, with
the marine phytoplankton organic matter dominates offshore and terrestrial plant organic matter
being important nearshore. The fluctuating trends in C/N ratio and δ
13C
POC indicated non-steady-state sedimentation. Overall, although spatial variability was observed across the
sampling region, the sediments were consistently characterized with shallow O
2 penetration and
high TOU. The strong correlation between sediment TOU and the low O
2 levels in the bottom
boundary layer suggests important contribution of sediment oxygen consumption to seasonal
hypoxia.
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