Diurnal Changes of pH and Alkalinity on the Coral Reefs of the Straits of Malacca, and

20 Pages·2015·1.48 MB·English

by  Abe Woo

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 PulauGaya
PulauBidong
PulauPayar
SOUTH CHINA SEA
Sumatra
400 km
STUDY
SITE
3 day period of observation at a shallow
water coral reef area
Hydrolab DS 5X recorded
Every 3 hours, water
reading every 15 minute In-situ measurement &
sample were collected
water sample collection
(pH, Temperature, Salinity,
and measured for the
Dissolved Oxygen, DO)
Total Alkalinity (A )
T
Aragonite saturation were determined
using the CO2SYS program (Lewis and
Wallace, 1998) through in situ A , pH,
T
salinity, temperature data.
Parameters Unit Measurement Methods
Temperature °C Hydrolab DS 5X
Salinity ppt Hydrolab DS 5X
pH Hydrolab DS 5X
Dissolved Oxygen (DO) mg/L Hydrolab DS 5X
Total Alkalinity µmol/kg Potentiometric Titration (Dickson et al., 2007)
Aragonite Saturation Ω CO2SYS program (Lewis and Wallace, 1998)
Aragonite
• 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 (A ) did not show any diurnal trend through out this study.
T
• However, the largest range of A was recorded at Payar with the value of 28.92 μmol/kg.
T
• Changes in A can be attributed to calcification or carbonate dissolution (Murillo et al., 2014)
T
Parameter Symbol Unit Pulau Payar Pulau Bidong Pulau Gaya
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 A μmol kg-1 2140.77± 6.29 2161.78± 3.08 2160.45± 3.41
T
pH pH 8.14 ± 0.02 8.01 ± 0.02 7.92 ± 0.01
T
ρCO in seawater ρCO μatm 288.59± 13.56 420.11± 22.86 531.47± 17.00
2 2
Carbonic acid H CO μmol kg-1 7.36 ± 0.36 10.66 ± 0.63 13.30 ± 0.51
2 3
Bicarbonate ion HCO - μmol kg-1 1523.50± 18.55 1654.45± 18.86 1718.85± 13.03
3
Carbonate ion CO 2- μmol kg-1 250.49± 6.65 206.22± 8.25 179.82± 5.48
3
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 Ω 6.25 ± 0.17 5.12 ± 0.21 4.48 ± 0.14
calc
Aragonite saturation Ω 4.16 ± 0.11 3.41 ± 0.14 2.99 ± 0.10
arag
Lower pH value and higher
Lower salinity and total
total alkalinity than Payar
alkalinity but higher pH
Parameter Symbol Unit Pulau Payar Pulau Bidong Pulau Gaya
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 A μmol kg-1 2140.77± 6.29 2161.78± 3.08 2160.45± 3.41
T
pH pH 8.14 ± 0.02 8.01 ± 0.02 7.92 ± 0.01
T
ρCO in seawater ρCO μatm 288.59± 13.56 420.11± 22.86 531.47± 17.00
2 2
Carbonic acid H CO μmol kg-1 7.36 ± 0.36 10.66 ± 0.63 13.30 ± 0.51
2 3
Bicarbonate ion HCO - μmol kg-1 1523.50± 18.55 1654.45± 18.86 1718.85± 13.03
3
Carbonate ion CO 2- μmol kg-1 250.49± 6.65 206.22± 8.25 179.82± 5.48
3
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 Ω 6.25 ± 0.17 5.12 ± 0.21 4.48 ± 0.14
calc
Aragonite saturation Ω 4.16 ± 0.11 3.41 ± 0.14 2.99 ± 0.10
arag
More carbonate ion
Lower carbonate ion
available in the seawater
concentration