46
available mineral surfaces multiplied by the typical OC loading, the excess OC will
not be preserved long term but will eventually remineralize unless it is structurally
recalcitrant. It has been demonstrated experimentally that OC tightly associated
with a sediment mineral surface can be rapidly remineralized by bacteria once it
physically detaches from the mineral surface (Keil et al. 1994b), and conversely,
that the enzymatic degradation rate of simple soluble organic molecules can be
drastically retarded by adsorption to a mesoporous mineral matrix (Zimmerman
et al. 2004). The nature and origin of organic matter adsorbed onto sediment mineral
surfaces, the exact mechanism of stability enhancement by adsorption, and the factors leading to maximal OC loading are currently unknown. One of the most likely
sources of adsorbed organic matter is extracellular polymeric substances, such as
acidic heteropolysaccharides, produced by indigenous bacteria, which can bind to
mineral surfaces via mechanisms such as ligand exchange, hydrogen bonding, van
der Waals forces, and cation bridges (Chenu 1993; Decho 2000; Lünsdorf et al.
2000; Nguyen and Harvey 2001). In fact, most organic matter detached from sediment minerals by ultrasonic and/or chemical treatments exhibits molecular weights
>10,000 (Miyajima et al. 2001a; Nunn and Keil 2005). It may be hypothesized that
the stereochemical structure of these macromolecules is determined by multiple
Estuarine Z. marina meadows
Gap zone among Z. marina meadows
Non-estuarine Z. marina meadows
Shallow pelagic sediment
0
1 0
2 0
3 0
0
500
1000
1500
2000
OC [µmol g ]
0
1 0
2 0
3 0
0
500
1000
1500
2000
SSA [m
2 g ]
OC [µmol g ]
Seagrass meadows on non-carbonate sediment
Seagrass meadows on carbonate sediment
Mangrove-fringed E. acoroides meadows
a
b
Fig. 2.5 Correlation between the OC concentration and specific surface area (SSA) of sediment in
various types of seagrass meadows. (a) Temperate seagrass meadow and pelagic sediments
collected from the Seto Inland Sea (central Japan); (b) subtropical and tropical seagrass meadow
sediments collected from Ishigaki Island (southwestern Japan), Bolinao (northern Philippines),
and Kuraburi (southern Thailand). Average OC loading was estimated by linear regression as 60.0
(non-estuarine Z. marina meadows), 55.5 (pelagic sediment of the Seto Inland Sea), 295 (tropical
and subtropical seagrass meadows on carbonate sediment), 44.3 (tropical and subtropical seagrass
meadows on non-carbonate sediment), and 86.4 μmol OC m
−2 (mangrove-fringed E. acoroides
meadows). (Data source: (a) Miyajima et al. (2017); (b) Miyajima et al., unpublished data)
T. Miyajima and M. Hamaguchi
available mineral surfaces multiplied by the typical OC loading, the excess OC will
not be preserved long term but will eventually remineralize unless it is structurally
recalcitrant. It has been demonstrated experimentally that OC tightly associated
with a sediment mineral surface can be rapidly remineralized by bacteria once it
physically detaches from the mineral surface (Keil et al. 1994b), and conversely,
that the enzymatic degradation rate of simple soluble organic molecules can be
drastically retarded by adsorption to a mesoporous mineral matrix (Zimmerman
et al. 2004). The nature and origin of organic matter adsorbed onto sediment mineral
surfaces, the exact mechanism of stability enhancement by adsorption, and the factors leading to maximal OC loading are currently unknown. One of the most likely
sources of adsorbed organic matter is extracellular polymeric substances, such as
acidic heteropolysaccharides, produced by indigenous bacteria, which can bind to
mineral surfaces via mechanisms such as ligand exchange, hydrogen bonding, van
der Waals forces, and cation bridges (Chenu 1993; Decho 2000; Lünsdorf et al.
2000; Nguyen and Harvey 2001). In fact, most organic matter detached from sediment minerals by ultrasonic and/or chemical treatments exhibits molecular weights
>10,000 (Miyajima et al. 2001a; Nunn and Keil 2005). It may be hypothesized that
the stereochemical structure of these macromolecules is determined by multiple
Estuarine Z. marina meadows
Gap zone among Z. marina meadows
Non-estuarine Z. marina meadows
Shallow pelagic sediment
0
1 0
2 0
3 0
0
500
1000
1500
2000
OC [µmol g ]
0
1 0
2 0
3 0
0
500
1000
1500
2000
SSA [m
2 g ]
OC [µmol g ]
Seagrass meadows on non-carbonate sediment
Seagrass meadows on carbonate sediment
Mangrove-fringed E. acoroides meadows
a
b
Fig. 2.5 Correlation between the OC concentration and specific surface area (SSA) of sediment in
various types of seagrass meadows. (a) Temperate seagrass meadow and pelagic sediments
collected from the Seto Inland Sea (central Japan); (b) subtropical and tropical seagrass meadow
sediments collected from Ishigaki Island (southwestern Japan), Bolinao (northern Philippines),
and Kuraburi (southern Thailand). Average OC loading was estimated by linear regression as 60.0
(non-estuarine Z. marina meadows), 55.5 (pelagic sediment of the Seto Inland Sea), 295 (tropical
and subtropical seagrass meadows on carbonate sediment), 44.3 (tropical and subtropical seagrass
meadows on non-carbonate sediment), and 86.4 μmol OC m
−2 (mangrove-fringed E. acoroides
meadows). (Data source: (a) Miyajima et al. (2017); (b) Miyajima et al., unpublished data)
T. Miyajima and M. Hamaguchi