Diurnal Changes of pH and Alkalinity on the Coral Reefs of the

Diurnal Changes of pH and Alkalinity on the Coral Reefs of the

The Diurnal Changes of Seawater pH and
Alkalinity on the Coral Reefs of the Strait
of Malacca and the South China Sea
Zulfigar Yasin1,2, Nithiyaa Nilamani1, Norhanis Razalli1,
Zulfikar3 and Aileen Tan Shau Hwai1
1Marine
Science Lab, School of Biological Sciences, Universiti Sains Malaysia,
11800 Minden, Penang, Malaysia.
2Institute of Oceanography and Environment (INOS), Universiti Terengganu Malaysia, 21030 Kuala Terengganu,
Terengganu, Malaysia.
3Universitas Malikussaleh, Lhokseumawe, Provinsi Acheh, Indonesia.
To investigate the diurnal variation of the seawater pH
and alkalinity in shallow water coral reef of Pulau Payar
(Strait of Malacca), Pulau Bidong and Pulau Gaya
(South China Sea)
N
Tarutao
National Park
Pulau Gaya
Pulau Bidong
Pulau Payar
SOUTH CHINA SEA
Sumatra
400 km
STUDY
SITE
3 day period of observation at a shallow
water coral reef area
Hydrolab DS 5X recorded
reading every 15 minute
(pH, Temperature, Salinity,
Dissolved Oxygen, DO)
In-situ measurement &
water sample collection
Aragonite saturation were determined
using the CO2SYS program (Lewis and
Wallace, 1998) through in situ AT, pH,
salinity, temperature data.
Every 3 hours, water
sample were collected
and measured for the
Total Alkalinity (AT)
Parameters
Unit
Measurement Methods
Temperature
°C
Hydrolab DS 5X
Salinity
ppt
Hydrolab DS 5X
Hydrolab DS 5X
pH
Dissolved Oxygen (DO)
mg/L
Hydrolab DS 5X
Total Alkalinity
µmol/kg
Potentiometric Titration (Dickson et al., 2007)
Aragonite Saturation
ΩAragonite
CO2SYS program (Lewis and Wallace, 1998)
• Decreasing surface
seawater pH trend from
the Strait of Malacca to
the South China Sea
more basic
less basic
day
night
day
night
day
night
Payar (SOM)
Bidong (SCS)
Gaya (SCS)
• pH trend fluctuates daily following the diurnal pattern which is regulated by
the biological activity such as photosynthesis and respiration
day
night
day
night
day
night
Gaya (SCS)
Bidong (SCS)
Payar (SOM)
•
•
•
Total alkalinity (AT) did not show any diurnal trend through out this study.
However, the largest range of AT was recorded at Payar with the value of 28.92 μmol/kg.
Changes in AT can be attributed to calcification or carbonate dissolution (Murillo et al., 2014)
Parameter
Symbol
Unit
Temperature
T
°C
29.96 ± 0.13
30.05 ± 0.30
30.70 ± 0.52
Salinity
S
ppt
32.02 ± 0.14
32.60 ± 0.07
32.46 ± 0.08
Total Alkalinity
AT
μmol kg-1
2140.77 ± 6.29
2161.78 ± 3.08
2160.45 ± 3.41
8.14 ± 0.02
8.01 ± 0.02
7.92 ± 0.01
288.59 ± 13.56
420.11 ± 22.86
531.47 ± 17.00
pH
pHT
Pulau Payar
Pulau Bidong
Pulau Gaya
ρCO2 in seawater
ρCO2
μatm
Carbonic acid
H2CO3
μmol kg-1
7.36 ± 0.36
10.66 ± 0.63
13.30 ± 0.51
Bicarbonate ion
HCO3-
μmol kg-1
1523.50 ± 18.55
1654.45 ± 18.86
1718.85 ± 13.03
Carbonate ion
CO32-
μmol kg-1
250.49 ± 6.65
206.22 ± 8.25
179.82 ± 5.48
Hydrogen ion
H+
μmol kg-1
7.32 x 10-3 ± 0.00
9.83 x 10-3 ± 0.00
1.19 x 10-2 ± 0.00
Calcite saturation
Ωcalc
6.25 ± 0.17
5.12 ± 0.21
4.48 ± 0.14
Aragonite saturation
Ωarag
4.16 ± 0.11
3.41 ± 0.14
2.99 ± 0.10
Lower pH value and higher
total alkalinity than Payar
Lower salinity and total
alkalinity but higher pH
Parameter
Symbol
Unit
Temperature
T
°C
29.96 ± 0.13
30.05 ± 0.30
30.70 ± 0.52
Salinity
S
ppt
32.02 ± 0.14
32.60 ± 0.07
32.46 ± 0.08
Total Alkalinity
AT
μmol kg-1
2140.77 ± 6.29
2161.78 ± 3.08
2160.45 ± 3.41
8.14 ± 0.02
8.01 ± 0.02
7.92 ± 0.01
288.59 ± 13.56
420.11 ± 22.86
531.47 ± 17.00
pH
pHT
Pulau Payar
Pulau Bidong
Pulau Gaya
ρCO2 in seawater
ρCO2
μatm
Carbonic acid
H2CO3
μmol kg-1
7.36 ± 0.36
10.66 ± 0.63
13.30 ± 0.51
Bicarbonate ion
HCO3-
μmol kg-1
1523.50 ± 18.55
1654.45 ± 18.86
1718.85 ± 13.03
Carbonate ion
CO32-
μmol kg-1
250.49 ± 6.65
206.22 ± 8.25
179.82 ± 5.48
Hydrogen ion
H+
μmol kg-1
7.32 x 10-3 ± 0.00
9.83 x 10-3 ± 0.00
1.19 x 10-2 ± 0.00
Calcite saturation
Ωcalc
6.25 ± 0.17
5.12 ± 0.21
4.48 ± 0.14
Aragonite saturation
Ωarag
4.16 ± 0.11
3.41 ± 0.14
2.99 ± 0.10
More carbonate ion
available in the seawater
Lower carbonate ion
concentration
GBP
G – Gaya
B – Bidong
P – Payar
Pulau Bidong and Pulau Gaya (South China Sea)

Higher AT were recorded at these sites, 2161.78 μmol kg-1 and 2160.45 μmol kg-1
respectively.

The pH at both sites in the South China Sea are lower than Paya (St of Malacca) as
denoted by the higher H+ concentration in the seawater.

Aragonite saturation in the seawater at both sites were recorded at adequate (3.41)
and marginal (2.99) level respectively.
Pulau Payar (Strait of Malacca)

Lower AT (2140.77 μmol kg-1) means the capacity of the seawater buffer system to
neutralize acidic pollution is reduced.

At present, the seawater carbonate system is maintained because of the pH value
(pH 8.14).

Only a small amount of acidic pollution is needed to disrupt the carbonate system
equilibrium.

Optimal aragonite saturation state in Payar contributes to the high coral calcification
rate in the area.
Parameter
Symbol
Unit
Temperature
T
°C
Total Alkalinity
AT
μmol kg-1
pH
pHT
Pulau Payar
Pulau Bidong
Pulau Gaya
29.96 ± 0.13
30.05 ± 0.30
30.70 ± 0.52
2140.77 ± 6.29
2161.78 ± 3.08
2160.45 ± 3.41
8.14 ± 0.02
8.01 ± 0.02
7.92 ± 0.01
ρCO2 in seawater
ρCO2
μatm
288.59 ± 13.56
420.11 ± 22.86
531.47 ± 17.00
Bicarbonate ion
HCO3-
μmol kg-1
1523.50 ± 18.55
1654.45 ± 18.86
1718.85 ± 13.03
Carbonate ion
CO32-
μmol kg-1
250.49 ± 6.65
206.22 ± 8.25
179.82 ± 5.48
Calcite saturation
Ωcalc
6.25 ± 0.17
5.12 ± 0.21
4.48 ± 0.14
Aragonite saturation
Ωarag
4.16 ± 0.11
(Optimal)
3.41 ± 0.14
(Adequate)
2.99 ± 0.10
(Marginal)
Source: Reefs at Risk Revisited (2011)
Calcification Rate of Porites sp.
(g cm-2 yr-1)
Strait of Malacca
SW of South
China Sea
SE of South
China Sea
2.1 (Payar)
Tanzil et al., 2013
2.1 (Redang)
Tanzil et al., 2013
0.7 (Spratly
Islands)
Ruixia et al., 2012






Studies on calcification rates and reef integrity in the region taking
into consideration local stressors
Develop and agree on a common methodology for the monitoring
of ocean acidification on coral reefs
Increase the number and spread of long term monitoring sites and
separation between OA and other anthropogenic effects on reefs
Develop baseline carbonate chemistry information and data sharing
for the Southeast Asia region and selected Class III sites.
Consider the depth of certain reefs and the effect OA on these and
associated biota
Integrate the findings of this group with the other physical and
chemical approaches of ocean acificication studies and beyond.
Relate to socio-economics of reef use and especially to fisheries.






Studies on calcification rates and reef integrity in the region
Increase the number and spread of long term monitoring sites
and separation between OA and other anthropogenic effects
on reefs
Develop and agree on a common methodology for the
monitoring of ocean acidification on coral reefs
Develop baseline carbonate chemistry information and data
sharing for the Southeast Asia region and selected Class III
sites.
Consider the depth of certain reefs and the effect OA on
these and associated biota
Integrate the findings of this group with the other physical and
chemical approaches of ocean acificication studies and
beyond. Relate to socio-economics of reef use and especially
to fisheries.
Pulau Payar
St.
A
St.
B
St.
C
St.
D

Caulastrea
Latitude
Genera

Montastrea
Acropora


Pectinia

Symphyllia



Diploastrea



D
C
B
A
Favia



Favites




Goniastrea




Porites




Total
4
8
7
7
Longitude
Template of study is adopted for reef monitoring studies by the
Malaysia’s Marine Park in collaboration with Universiti Malaysia
Terengganu and Universiti Sains Malaysia.
Current location of monitoring stations are in the:
• Straits of Malacca (Sabang and Langkawi)
• Eastern portion of the South China Sea (Bidong, Terengganu)
• Western portion of the South China Sea (Pulau Gaya, Kota Kinabalu
We wish to thank the following institutions for their
generous suport:
Ministry of Science and Technology of Malaysia
(MOSTI)
Ministry of Natural Resources and Environment (NRE)
The Marine Park Department of Malaysia
Universiti Sains Malaysia (USM)
Universiti Malaysia Terengganu (UMT)
Thank you for your kind attention
[email protected]