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International Journal of Marine Science 2014, Vol.4, No.1, 1-15
http://ijms.sophiapublisher.com
3
20 cm ht.) to prevent the chamber from emerging out
of the water during low tide. Before beginning the
incubations, each habitat was cleared of benthic
macroalgae, snails and other visible macrofauna to
minimize other variables that could affect the
inorganic nitrogen and carbon dynamics. In the SD
habitat, the contributions of phytoplankton and/or
other microorganisms in benthos and water column
were estimated as a control.
2.3 Chemical and environmental parameters
Seawater samples were collected by syringe at the
beginning and end of each of the incubations. The pH
and total alkalinity (TA) were determined using a pH
electrode (pH meter Orion 4-star, Thermo-Fisher
Scientific) on the NBS scale and the Gran plot method
using a total alkalinity titrator (ATT-05, Kimoto),
respectively. Accuracy of these measurement were
±0.05 for pH and ±10 µmol kg
-1
for TA. Salinity (S)
was measured by a salinometer (Portsal 8410A,
Guildline) based on comparison with IAPSO standard
water (S = 34.993). Ammonium, nitrate, and nitrite
ions were measured by an automatic water analyzer
(QuAAtro, BRAN+LUEBBE).
Data loggers (Water Temp Pro v2 Data Logger, HOBO)
and photon sensors (MDS-MkV/L, Alec Electronics
Co.) were deployed beside the chamber to record
temperature and photon flux. Tidal level data were
provided by the Okinawa Meteorological Observatory.
2.4 Groundwater inflow
Groundwater comes out of sediment through the
limestone. To examine the effects of groundwater
outflow into the reef moat, the initial total alkalinity
(TA), nitrate + nitrite (NO
x
), and ammonium (NH
4
+
)
concentrations during the lowest spring tides (1-Aug,
12:00, 1-Aug, 16:00, and 4-Aug, 16:00) of the
sampling period were plotted against salinity (S).
The slope of each regression line (R
slope
) was used
to calculate the change in concentration (∆C
inflow
)
due to groundwater inflow during the chamber
incubation.
∆C
inflow
= R
slope
• ∆S
final-initial
(Eq.1)
where ∆C
inflow
is the inflow concentration of total
alkalinity, NO
x
or NH
4
+
, R
slope
is the slope of each
regression line in Figure 3, ∆S
final-initial
is the difference
in salinity between final and initial samples in each
incubation chamber.
2.5 Data analysis
The difference between chemical constituents in each
chamber over a given period was attributed to
biological activity. However, as we detected a
decrease in salinity during the incubations, most of the
chambers in this study were influenced by
groundwater inflow. Therefore, we accounted for the
effect of inflowing water to estimate the biological
activity as follows:
∆C
biological
= C
final
- C
initial
- ∆C
inflow
(Eq.2)
Where, ∆C
biological
is the change in TA, DIC, NO
x
, or
NH
4
+
during an incubation due to the biological
activity within a given chamber.
Using the ∆C
biological
of total alkalinity (TA) and total
dissolved inorganic carbon (DIC) data, the rates of
organic carbon production (OP, mmol m
–2
h
–1
) and
inorganic carbon production (IP, mmol m
–2
h
–1
) were
calculated using the alkalinity anomaly technique
(Smith 1973, Smith and Kinsey 1978). IP was
expressed by using: the changes in TA, volume of the
chamber (V), base area of the chamber (A) and
incubation time (t), as follows:
(Eq. 3)
OP was calculated by using the changes in total
dissolved inorganic carbon (DIC), volume of chamber
(V), the base area of chamber (A), incubation time (t)
and IP, as follows:
(Eq. 4)
Total dissolved inorganic carbon (DIC) was also
calculated using pH, total alkalinity (TA), and
equilibrium constants for the carbonate system, as
follows:
(Eq. 5)
where DIC is the total dissolved inorganic carbon
(µmol kg
–1
), TA is the total alkalinity (µmol kg
–1
), a
H
+
is the activity of hydrogen ions (i.e. = 10
–pH
), K'
1
is the
apparent first dissociation constant of carbonate ions
tA2
V
TA -
IP
biological
⋅ ⋅
⋅
Δ
=
IP
tA
V
DIC
OP
biological
−
⋅
⋅
Δ−
=
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
+
⋅
× ⋅
− ⋅
+
+
+
=
+
+
+
+
−
B
H
5
B
2
H 1
2 1
H 1
2
H
'K a
S 10
1.212
'K TA
) ' 2K (a 'K
'K'K a'K a
DIC