376
3
Results and Discussion
3.1
Biogeochemical Services
Mangrove ecosystems are thought to provide the
following services to humans directly or
indirectly:
• Storage of high quantities of organic materials
and nutrients. Mangroves grow mainly in river
mouth regions, environments inclined toward
the accumulation of various types of substances that fl ow from rivers. Mangroves
therefore function as warehouses for the storage of high quantities of organic materials and
nutrients.
• Sources of organic matter supply. Large
amounts of leaves, twigs, and fl owers from
mangrove plants fall to the mangrove forest
fl oors, eventually breaking down and providing organic material to surrounding tidal fl ats
and coastal areas. This material becomes food
for small animals and serves as an important
food source for coastal living organisms.
These two services can be clarifi ed by future
research into the dynamics of organic materials
around mangrove areas.
The topography of this area is unique. A road
named Compact Road, which runs around the
whole of Babeldaob Island, crosses the bay,
forming an enclosed lagoon.
Two small culverts have been used as passages for small boats. Waters in the lagoon are
characterized by poor visibility and were
observed to contain large amounts of suspended
matter. Water fl ow and currents are mild.
However, waters on the opposite side of the road
were found to be comparatively clear. This suggests that little water exchange takes place
between the lagoon and outer waters.
However, waters surrounding the culverts are
constantly exchanged due to tidal movements as
well as outfl ow from the lagoon to the waters
beyond. Stable isotope analysis has become a
popular method for understanding food webs in
aquatic ecosystems because carbon and nitrogen
stable isotopes can reveal the organic carbon
sources of primary producers. In this research,
we analyzed sediments to examine the sources of
organic materials. Unfortunately, nitrogen levels
were so low that detection was problematic.
In sediments, organic materials from the
lagoon were derived from mangrove plants,
whereas those outside the lagoon were derived
from phytoplankton. The effects of the physical
structure of this area are clear.
Comparatively higher contents of calcium carbonate, higher than 80 % in some cases (1–5),
were found at several stations. Calcium carbonate is considered to be biologically derived from
corals, shellfi sh, and foraminiferans. As such, the
above observations showed that, with the exception of river regions, bottom sediments in the
marine areas surveyed had been infl uenced
greatly by coral reefs.
Total organic content analysis produced suggests the formation of an environment where
organic matter outfl ow from rivers tends to accumulate. At some sites inside the lagoon area,
comparatively higher contents of organic substances were detected.
C/N ratio analysis of sediment samples taken
from sites located between the estuarine region
(6) and upper reaches of the river (7 and 8) exhibited higher values.
Commonly, high values for sediments containing substances derived from higher plants
with thick cell walls suggest that a survey site,
beginning with its mangroves, contains a signifi -
cant accumulation of matter derived from higher
plants.
Early observations of the coral reefs and mangroves of Palau inspired questions about the
infl uences of the vast mangrove systems on coral
reefs. It thus seems clear that massive quantities
of fallen leaves will affect the quality of surrounding waters and bottom sediments, while
generating a relationship with the biota inhabiting river mouths and coastal zones.
Golbuu et al. ( 2003 ) investigated sediment
behavior in semi-closed environments of river
mouths in the Ngerikiil River in Airai State. While
watersheds in this area maintained comparatively
good environmental conditions up until the 1970s,
the construction of the International Airport during 1978–1982 and lowland agriculture, which
M. Tsuchiya et al.
3
Results and Discussion
3.1
Biogeochemical Services
Mangrove ecosystems are thought to provide the
following services to humans directly or
indirectly:
• Storage of high quantities of organic materials
and nutrients. Mangroves grow mainly in river
mouth regions, environments inclined toward
the accumulation of various types of substances that fl ow from rivers. Mangroves
therefore function as warehouses for the storage of high quantities of organic materials and
nutrients.
• Sources of organic matter supply. Large
amounts of leaves, twigs, and fl owers from
mangrove plants fall to the mangrove forest
fl oors, eventually breaking down and providing organic material to surrounding tidal fl ats
and coastal areas. This material becomes food
for small animals and serves as an important
food source for coastal living organisms.
These two services can be clarifi ed by future
research into the dynamics of organic materials
around mangrove areas.
The topography of this area is unique. A road
named Compact Road, which runs around the
whole of Babeldaob Island, crosses the bay,
forming an enclosed lagoon.
Two small culverts have been used as passages for small boats. Waters in the lagoon are
characterized by poor visibility and were
observed to contain large amounts of suspended
matter. Water fl ow and currents are mild.
However, waters on the opposite side of the road
were found to be comparatively clear. This suggests that little water exchange takes place
between the lagoon and outer waters.
However, waters surrounding the culverts are
constantly exchanged due to tidal movements as
well as outfl ow from the lagoon to the waters
beyond. Stable isotope analysis has become a
popular method for understanding food webs in
aquatic ecosystems because carbon and nitrogen
stable isotopes can reveal the organic carbon
sources of primary producers. In this research,
we analyzed sediments to examine the sources of
organic materials. Unfortunately, nitrogen levels
were so low that detection was problematic.
In sediments, organic materials from the
lagoon were derived from mangrove plants,
whereas those outside the lagoon were derived
from phytoplankton. The effects of the physical
structure of this area are clear.
Comparatively higher contents of calcium carbonate, higher than 80 % in some cases (1–5),
were found at several stations. Calcium carbonate is considered to be biologically derived from
corals, shellfi sh, and foraminiferans. As such, the
above observations showed that, with the exception of river regions, bottom sediments in the
marine areas surveyed had been infl uenced
greatly by coral reefs.
Total organic content analysis produced suggests the formation of an environment where
organic matter outfl ow from rivers tends to accumulate. At some sites inside the lagoon area,
comparatively higher contents of organic substances were detected.
C/N ratio analysis of sediment samples taken
from sites located between the estuarine region
(6) and upper reaches of the river (7 and 8) exhibited higher values.
Commonly, high values for sediments containing substances derived from higher plants
with thick cell walls suggest that a survey site,
beginning with its mangroves, contains a signifi -
cant accumulation of matter derived from higher
plants.
Early observations of the coral reefs and mangroves of Palau inspired questions about the
infl uences of the vast mangrove systems on coral
reefs. It thus seems clear that massive quantities
of fallen leaves will affect the quality of surrounding waters and bottom sediments, while
generating a relationship with the biota inhabiting river mouths and coastal zones.
Golbuu et al. ( 2003 ) investigated sediment
behavior in semi-closed environments of river
mouths in the Ngerikiil River in Airai State. While
watersheds in this area maintained comparatively
good environmental conditions up until the 1970s,
the construction of the International Airport during 1978–1982 and lowland agriculture, which
M. Tsuchiya et al.