International Journal of Oceans and Oceanography
ISSN 0973-2667 Volume 10, Number 1 (2016), pp. 29-48
© Research India Publications
http://www.ripublication.com
Dissolved Organic (DOC) and Inorganic Carbon
(DIC) and Its Distribution in the Nearshore Waters of
Port Blair, Andaman Islands, India
P. M. Mohan1*, R. K. Kumari1, M. Muruganantham1,
V. V. Ubare1, C. Jeeva1 and S. Chakraborty2
1
* Department of Ocean Studies and Marine Biology,
Pondicherry University, Brookshabad, Port Blair,
Andaman and Nicobar Islands, India.
2
Indian Institute of Tropical Meteorology,
Ministry of Earth Sciences, Pune, India.
Abstract
The marine waters are mainly influenced by the changes in air-sea
interactions, terrestrial run off and various ecological and biological processes
and in turn provide Dissolved Organic (DOC) and Inorganic Carbon (DIC). In
the present study a combination of physical and chemical studies were carried
out to understand their impact on near shore surface waters distribution of
DOC and DIC. The waters were collected from surface to 15m with the depth
interval of 5m during July 2014 to February 2015, from three stations namely
Chatham, North Bay and Carbyns Cove which differed from each other in
terms of ecology and geomorphologic distributions. Chatham represented an
area influenced by ship transits, mangrove inputs and anthropogenic activities,
Carbyns Cove represented mainly an open sea influenced area and North Bay
maintained a pristine coralline environment without much terrestrial input.
The samples were analyzed for pH, temperature, salinity, DIC and DOC. The
results suggested that temperature increment would not lower the pH and it
was supported by the fact that high temperature reduces the dissolution and
retention capacity of gases by water. The DOC was provided to this nearshore
oligotrophic waters by the land based organic carbon around the level of 50 to
150 µM/L. The dissolution of carbonate soil and rocks provided the DIC to
the tune of 300 µM/L. Over and above, it was found out the rainwater may
also be provided around 100 µM/L of DIC to these nearshore waters.
Keywords: DOC, DIC, Nearshore, Port Blair, Andaman Islands.
30
P.M. Mohan et al
INTRODUCTION
The ocean is the largest carbon reservoir and a major sink for the anthropogenic
carbon. Carbon is available as both organic and inorganic forms in both particulate
and dissolved state. Organic matter though present in small amount it plays an
important role in establishing the properties of sea water and the processes taking
place there including, water colour and the speciation of chemical trace constituents,
the latter, light scattering, migration and bioavailability of heavy metals1. It is
assumed that organic carbon (OC) constitutes 45% of organic matter (OM), although
other proportions have been reported2. Organic matter can be separated into
particulate (POM) and dissolved (DOM) species.
Dissolved organic carbon (DOC) is considered the largest organic reservoir in the
ocean and it plays a central role in the marine biogeochemical cycle of carbon3, 4.
Coastal and marginal seas play a key role in the global carbon cycle by linking
terrestrial, oceanic, and atmospheric reservoirs5. Biological process are considered to
be the primary factor controlling the accumulation of DOC, but there is a poor
correlation between carbon storage as DOC and rates of primary production as
reported by Menzel6. Similarly, Peltzer and Hayward7 found the highest
concentrations of OC where waters were most oligotrophic in the equatorial Pacific,
which suggests physical control in the distribution of DOC in surface and deep layers
of ocean. Hansell and Waterhouse8 reported that water column stability imparted by
the main thermocline plays a significant role in supporting the surface layer storage of
carbon. The international research programs like Joint Global Ocean Flux Study,
World Ocean Circulation Experiment, etc., in the last decade, have improved the
broad understanding about the distribution and cycling of inorganic and organic
carbon in the ocean. However, there much to be studied about the contribution of
coastal water to the global biogeocycle of organic carbon. Furthermore, concern over
impact of anthropogenic CO2 in the oceans and climatic change has become an area of
high interest. In this regard, it is essential to understand the fundamental process of
DOC and DIC distribution and its controlling process. The DIC mainly influenced by
biological pump. The process of carbon removal by the primary producers and its
subsequent remineralisation to inorganic component after decomposition is termed as
biological pump. The direct gas exchange between the surface waters and the
atmosphere is also an important source of inorganic carbon concentration. Moreover,
dissolution of carbonate particles from the sediments also adds to the concentration.
Recent works have suggested that the majority of open ocean carbonate is exported
from the surface layer, well above the calcite lysocline. According to report by Ogawa
and Tanoue9 labile DOM are mainly available in the shallower region of the ocean,
mostly in the euphotic zone related primary production. So, it is essential to
understand the shallow water process of DOC and DIC in the marine environment.
This study was focused on understanding the distribution of DOC and DIC in the
surface layers on oligotrophic coastal water off Port Blair, South Andaman. Although,
these waters are considered to be oligotrophic, the release of organic carbon rich
materials by the reef-building corals contributes substantially to biogeochemical
processes and rapid nutrient recycling in coral reef ecosystems. The climate of the
Andaman Sea is mostly determined by currents and monsoons of Southeast Asia i. e.
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
31
north-easterly and easterly in winter and south-westerly and westerly in summer.
These seasonal monsoons play a major role in freshwater input to the surface marine
water.
MATERIALS AND METHOD
The present study was carried out in the surface waters off Port Blair and three
locations each representing a different ecosystem was selected for understanding the
distribution of DOC and DIC in this area (Fig. 1). The seawater was collected using
Niskin water sampler at surface, 5m, 10m and 15m depths and filtered using a Glass
Fiber micro filter paper (Whattman GF/F), acidified with concentrated HCl to a pH of
2 and stored in 120 ml. The insitu physical parameters were measured using Quanta
Hydrolab. The DOC and DIC of the samples were estimated by a process of super
critical water oxidation (SCWO), as explained by Kumari et al. 10. The analytical error
for DOC and DIC is in the range of 1.5 to 3.0% level.
Figure 1: The Study Area
P.M. Mohan et al
32
RESULT AND DISCUSSIONS
The following study was conducted to understand the distribution and flux of organic
and inorganic carbon in the surface seawater of South Andaman, Off Port Blair. The
change in carbon was correlated with physical parameters such as temperature, pH
and salinity of different depths such as Surface, 5m, 10m and 15m, respectively, from
three locations namely Chatham, North Bay and Carbyns Cove (Table 1, 2, 3). All the
three regions differ significantly in their ecology as well as in geographic context.
Chatham is a small island located at the mouth of a inlet of sea with a close proximity
a saw mill and a jetty along with neighboring Port Blair Harbour with a larger level of
vessel movement between Islands. This part of the channel banks are covered with
mangrove vegetations. North Bay is opposite side of this jetty with a water distance of
around two nautical miles with good coral diversity and also a known tourist spot.
The rocky-sandy shore mainly covered with coconut plantation. The third locations
Carbyns Cove is a tourist spot, it is wide spread sandy beach and depth covers with
coral reef community, also receives inputs from nearby freshwater channel from
inland. The inland side of the channel has been covered with mangrove ecosystem and
shores are devoid of mangroves.
Table 1: Distribution of Temperature, pH, Salinity, Dissolved Organic Carbon (DOC)
and Dissolved Inorganic Carbon (DIC) for Chatham station.
Temperature °C
Chatham Surface
5m
10m
Jul-14
29. 5
29. 38 29. 11
Aug-14
29. 06 28. 67 28. 51
Sep-14
29. 02 28. 35 28. 06
Oct-14
30. 51 29. 02
28. 8
Nov-14
29. 91 29. 88 29. 82
Dec-14
29. 13 29. 74 29. 48
Jan-15
28. 73 28. 75 28. 67
Feb-15
28. 76 28. 72 28. 54
Chatham Surface
5m
10m
Minimum 28. 73 28. 35 28. 06
Maximum 30. 51 29. 88 29. 82
Average
29. 33 29. 06 28. 87
pH
Chatham Surface
5m
10m
Jul-14
8. 34
8. 22
8. 19
Aug-14
8. 07
8. 21
8. 25
Sep-14
8. 87
8. 88
8. 96
Oct-14
8. 27
8. 29
8. 24
Nov-14
8. 69
8. 41
8. 33
Dec-14
8. 23
8. 21
8. 22
Jan-15
8. 59
8. 54
8. 55
15m
28. 72
28. 44
28. 03
26. 75
29. 82
29. 25
28. 68
28. 47
15m
28. 75
29. 82
28. 52
15m
8. 14
8. 45
9. 03
8. 17
8. 31
8. 33
8. 59
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
Feb-15
8. 4
8. 3
Chatham Surface
5m
Minimum
8. 07
8. 21
Maximum 8. 87
8. 88
Average
8. 43
8. 38
Salinity PSU
Chatham Surface
5m
Jul-14
35. 4
35. 47
Aug-14
32. 4
34. 53
Sep-14
34. 18 35. 19
Oct-14
31. 51
34. 7
Nov-14
34. 37 34. 52
Dec-14
34. 96 34. 96
Jan-15
35. 06 35. 36
Feb-15
34. 2
34. 54
Chatham Surface
5m
Minimum 31. 51 34. 52
Maximum 35. 4
34. 47
Average
34. 01 34. 91
DOC µM/L
Chatham
Sur
5m
Jul-14
71. 00 108. 00
Aug-14
110. 50 123. 50
Sep-14
150. 00 139. 00
Oct-14
56. 00 98. 00
Nov-14
76. 00 43. 00
Dec-14
86. 00 82. 00
Jan-15
84. 00 112. 00
Feb-15
60. 00 144. 00
Chatham Surface
5m
Minimum 56. 00 43. 00
Maximum 150. 00 144. 00
Average
86. 59 106. 19
DIC µM/L
Chatham Surface
5m
Jul-14
93. 00 90. 00
Aug-14
88. 00 83. 50
Sep-14
80. 00 77. 00
Oct-14
20. 00
0. 00
Nov-14
283. 00 378. 00
Dec-14
93. 00 149. 00
Jan-15
97. 00 108. 00
Feb-15
218. 00 220. 00
33
8. 3
10m
8. 19
8. 96
8. 38
8. 2
15m
8. 14
9. 03
8. 4
10m
35. 53
34. 97
36. 07
35. 06
34. 67
34. 95
35. 36
34. 75
10m
34. 67
36. 07
35. 17
15m
35. 59
34. 97
36. 15
35. 06
34. 69
35. 16
35. 13
34. 75
15m
34. 69
36. 15
35. 19
10m
96. 00
119. 50
143. 00
103. 00
39. 00
114. 00
110. 00
99. 58
10m
39. 00
143. 00
103. 01
15m
111. 00
101. 00
91. 00
75. 00
53. 00
124. 00
93. 00
102. 00
15m
53. 00
124. 00
93. 75
10m
15m
87. 00 75. 00
80. 50 68. 50
74. 00 62. 00
0. 00
0. 00
333. 00 392. 00
106. 00 94. 00
103. 00 107. 00
220. 00 203. 00
P.M. Mohan et al
34
Chatham Surface
5m
10m
15m
Minimum 20. 00
0
0. 00
0
Maximum 283. 00 378. 00 333. 00
392
Average 121. 50 138. 19 125. 44 125. 19
Table 2: Distribution of Temperature, pH, Salinity, Dissolved Organic Carbon (DOC)
and Dissolved Inorganic Carbon (DIC) for North Bay station.
North Bay
Jul-14
Aug-14
Sep-14
Oct-14
Nov-14
Dec-14
Jan-15
Feb-15
North Bay
Minimum
Maximum
Average
North Bay
Jul-14
Aug-14
Sep-14
Oct-14
Nov-14
Dec-14
Jan-15
Feb-15
North Bay
Minimum
Maximum
Average
North Bay
Jul-14
Aug-14
Sep-14
Oct-14
Nov-14
Dec-14
Temperature °C
Surface
5m
29. 54
29. 27
29. 28
28. 11
28. 74
28. 31
30. 22
29. 31
29. 5
29. 5
29. 44
29. 43
28. 65
28. 66
28. 64
28. 48
Surface
5m
28. 64
28. 11
30. 22
29. 5
29. 25
28. 88
pH
Surface
5m
8. 48
8. 45
8. 52
8. 59
8. 7
8. 73
8. 15
8. 23
8. 17
8. 32
7. 97
8. 03
8. 37
8. 32
8. 4
8. 3
Surface
5m
7. 97
8. 03
8. 7
8. 73
8. 35
8. 37
Salinity PSU
Surface
5m
35. 55
35. 61
35. 23
35. 63
34. 98
35. 49
34. 61
34. 87
34. 65
34. 72
35. 02
35. 1
10m
29. 3
28
28. 15
28. 82
29. 51
29. 35
28. 65
28. 24
10m
28
29. 51
28. 75
15m
29. 21
27. 89
28. 11
28. 77
29. 51
29. 29
28. 66
27. 98
15m
27. 89
29. 51
28. 68
10m
8. 29
8. 45
8. 74
8. 27
8. 36
8. 06
8. 27
8. 3
10m
8. 06
8. 74
8. 34
15m
8. 13
8. 2
8. 76
8. 26
8. 37
8. 06
8. 47
8. 3
15m
8. 06
8. 76
8. 32
10m
35. 53
35. 77
35. 7
35. 07
34. 73
35. 09
15m
35. 61
35. 91
35. 85
35. 14
34. 8
35. 16
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
Jan-15
35. 2
35. 2
Feb-15
33. 71
34. 9
North Bay-Sur Surface
5m
Minimum
33. 71
34. 72
Maximum
35. 55
35. 63
Average
34. 87
35. 19
DOC µM/L
North Bay
Surface
5m
Jul-14
57. 00
93. 00
Aug-14
96. 50 108. 50
Sep-14
136. 00 124. 00
Oct-14
81. 00
82. 00
Nov-14
10. 00
0. 00
Dec-14
54. 00
91. 00
Jan-15
75. 00 149. 00
Feb-15
68. 00 104. 00
North Bay
Surface
5m
Minimum
10. 00
0. 00
Maximum
136. 00 149. 00
Average
72. 19
93. 94
DIC µM/L
North Bay
Surface
5m
Jul-14
95. 00
96. 00
Aug-14
88. 50
89. 50
Sep-14
82. 00
83. 00
Oct-14
7. 00
0. 00
Nov-14
367. 00 393. 00
Dec-14
121. 00 128. 00
Jan-15
108. 00 76. 00
Feb-15
212. 00 199. 00
North Bay
Sur
5m
Minimum
7. 00
0. 00
Maximum
367. 00 393. 00
Average
135. 06 133. 06
35
35. 28
34. 8
10m
34. 73
35. 77
35. 25
35. 28
34. 1
15m
34. 1
35. 91
35. 23
10m
132. 00
155. 50
179. 00
103. 00
3. 00
74. 00
108. 00
96. 00
10m
3. 00
179. 00
106. 31
15m
96. 00
86. 00
76. 00
109. 00
0. 00
62. 00
106. 00
107. 00
15m
0. 00
109. 00
80. 25
10m
91. 00
84. 50
78. 00
0. 00
171. 00
143. 00
84. 00
171. 00
10m
0. 00
171. 00
102. 81
15m
93. 00
86. 50
80. 00
0. 00
370. 00
150. 00
75. 00
188. 00
15m
0. 00
370. 00
130. 31
Table 3: Distribution of Temperature, pH, Salinity, Dissolved Organic Carbon (DOC)
and Dissolved Inorganic Carbon (DIC) for Carbyns Cove station.
Temperature °C
Carbyns Cove Surface
5m
10m
Jul-14
29. 41
29. 3
29. 18
Aug-14
28. 41 28. 39 28. 35
Sep-14
28. 44 28. 41 28. 41
Oct-14
29. 28
29. 3
28. 9
15m
29. 06
28. 21
28. 39
28. 81
P.M. Mohan et al
36
Nov-14
29. 36
Dec-14
29. 15
Jan-15
28. 64
Feb-15
28. 19
Carbyns Cove Surface
Minimum
28. 19
Maximum
29. 41
Average
28. 86
29. 37
29. 04
28. 68
28. 18
15m
28. 18
29. 37
28. 72
Carbyns Cove
Jul-14
Aug-14
Sep-14
Oct-14
Nov-14
Dec-14
Jan-15
Feb-15
Carbyns Cove
Minimum
Maximum
Average
15m
8. 13
8. 36
8. 6
8. 35
8. 41
8. 13
8. 52
8. 1
15m
8. 1
8. 6
8. 33
Carbyns Cove
Jul-14
Aug-14
Sep-14
Oct-14
Nov-14
Dec-14
Jan-15
Feb-15
Carbyns Cove
Minimum
Maximum
Average
Carbyns Cove
Jul-14
Aug-14
Sep-14
Oct-14
Nov-14
29. 4
29. 37
29. 18 29. 12
28. 66 28. 68
28. 17 28. 17
5m
10m
28. 17 28. 17
29. 4
29. 37
28. 85 28. 77
pH
Sur
5m
10m
8. 04
8. 08
8. 13
8. 27
8. 29
8. 31
8. 45
8. 57
8. 59
8. 26
8. 29
8. 32
8. 38
8. 42
8. 37
7. 98
8. 06
8. 11
8. 57
8. 35
8. 28
8. 3
8. 2
8. 1
Surface
5m
10m
7. 98
8. 06
8. 1
8. 57
8. 57
8. 59
8. 28
8. 28
8. 28
Salinity PSU
Surface
5m
10m
35. 61 35. 61 35. 68
35. 64 35. 71 35. 11
35. 79 35. 86 36. 01
34. 71 34. 94 35. 14
34. 72 34. 74 34. 72
35. 16 35. 23 35. 23
35. 28 35. 28
35. 8
34. 14 34. 43 34. 81
Surface
5m
10m
34. 14 34. 43 34. 72
35. 79 35. 86 36. 01
35. 13 35. 23 35. 31
DOC µM/L
Sur
5m
10m
62. 00 104. 00 73. 00
101. 50 119. 50 96. 50
141. 00 135. 00 120. 00
81. 00 133. 00 88. 00
14. 00 21. 00 52. 00
15m
35. 67
35. 71
36. 01
35. 21
34. 71
35. 37
34. 91
35. 25
15m
34. 71
36. 01
35. 36
15m
57. 00
47. 00
37. 00
88. 00
21. 00
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
Dec-14
61. 00 120. 00
Jan-15
44. 00 56. 00
Feb-15
64. 00 133. 00
Carbyns Cove Surface
5m
Minimum
14. 00 21. 00
Maximum
141. 00 135. 00
Average
71. 06 102. 69
DIC µM/L
Carbyns Cove Surface
5m
Jul-14
91. 00 95. 00
Aug-14
84. 50 88. 45
Sep-14
78. 00 82. 00
Oct-14
0. 00
0. 00
Nov-14
348. 00 307. 00
Dec-14
91. 00 88. 00
Jan-15
101. 00 122. 00
Feb-15
189. 00 200. 00
Carbyns Cove Surface
5m
Minimum
0. 00
0. 00
Maximum
348. 00 307. 00
Average
122. 81 122. 81
37
112. 00
100. 00
102. 00
10m
52. 00
120. 00
92. 94
110. 00
103. 00
106. 00
15m
21. 00
110. 00
71. 13
10m
122. 00
115. 50
109. 00
0. 00
292. 00
143. 00
78. 00
171. 00
10m
0. 00
292. 00
128. 81
15m
114. 00
108. 00
101. 00
0. 00
303. 00
134. 00
67. 00
194. 00
15m
0. 00
303. 00
127. 63
Physical Parameters :
Temperature observed in the study area of Chatham was in the range of 28.06 to
30.51°C from the surface to 15 m depth (Fig. 2). The average temperature during the
study period was in the range of 28.52 to 29.33°C. The second station North Bay (Fig.
3) represented 27.89 to 30.22°C of temperature from surface to 15 m depth with an
average of 28.68 to 29.25°C. The third station Carbyns Cove (Fig. 4) exhibited the
temperature in the range of 28.17 to 29.41°C and the average fall between 28.72 to
28.86°C.
The pH represented in the station Chatham ranged from 8.07 to 9.07 with an average
of 8.38 to 8.43 (Fig. 5). However, the station North Bay (Fig. 6) exhibited 7.97 to 8.76
ranges and average was between 8.32 to 8.37. The station Carbyns Cove (Fig. 7) pH
falls in the range of 7.98 to 8.60 with an average of 8.28 to 8.33.
The salinity noticed in the range of 31.51 to 36.15 PSU for the station Chatham (Fig.
8) with an average of 34.01 to 35.19 PSU. The range of salinity noticed for the station
North Bay (Fig. 9) was 33.71 to 35.91 PSU with an average of 34.87 to 35.25 PSU.
The station Carbyns Cove (Fig. 10) represented 34.14 to 36.01 PSU range of salinity
with an average of 35.13 to 35.36 PSU.
38
P.M. Mohan et al
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
39
40
P.M. Mohan et al
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
41
DOC and DIC Distribution:
The DOC represented for the station Chatham (Fig.11) in the range of 39 to 150
µM/L with an average of 86.59 to 106.19 µM/L. The stations North Bay (Fig.12)
exhibited ND to 179 µM/L of DOC with an average of 72.19 to 106.31 µM/L. The
station Carbyns Cove (Fig.13) showed a range of 14 to 141 µM/L level of DOC with
an average of 71.06 to 102.69 µM/L.
The DIC noticed for the station Chatham (Fig.14) was in the range of ND to 392
µM/L with an average of 121.50 to 138.19 µM/L. The station North Bay (Fig.15)
represented ND to 393 µM/L range of DIC with an average of 102.81 to 135.06
µM/L. Carbyns Cove (Fig. 16) station represented the DIC value in the range of ND
to 348 µM/L with the average of 122.81 to 128.81 µM/L.
42
P.M. Mohan et al
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
43
DISCUSSION
The station Chatham exhibited a range of 2.45°C variation among the study period
which was highest among the studied stations, i. e. North Bay and Carbyns Cove
represented the differences of temperature, respectively 2.33°C and 1.24°C. This may
be interpreted that the fresh water input routed through the channel was not mixed
well and thus remained as layered water mass. However, in the case of North Bay,
even though such channelization of fresh water was not available but the natural pour
of rainwater formed the layered water mass. This may be because of bay nature which
was devoid of much agitation due to the less wave action. The station Carbyns Cove
exhibited the least differences of temperature between the surface to 15 m depth
during the study period which suggested that it may be due to the open ocean
condition, the constant wave action which in turn mix the freshwater input with faster
mixing of layers. The temperature difference of 1°C among the studied stations
suggested that it was a common phenomena and it may due to the physical process as
reported in Hawoland Island in Hawaii11. Grodsky et al.12 reported that due to the
mixing of waves the Equatorial Atlantic Mixed Layer was warmed up to 0.35°C
during the year 2002 support the above inferences that wave action may warm up the
layered waters.
The pH also exhibited almost similar trend of temperature i. e the highest differences
noticed between the range in Chatham followed by North Bay and Carbyns Cove,
respectively, 0.96, 0.79 and 0.62. This factor also supports the above inferences
without any ambiguity. Another interesting factor noticed in this study was that the
pH shifted more towards alkalinity with any raise in temperature, i. e. Chatham
station, average values of temperature and pH suggested that 29.33°C with 8.4 and
28.52°C with 8.20, where a clear rainwater layering existed. This factor was against
the current concept that the increment of temperature reduces the alkalinity. Sridhar et
al.13, reported similar kind of inferences in their study in Palk Bay, off Tamil Nadu
44
P.M. Mohan et al
coast, region. Kannapiran et al.14, evolved a similar kind of database for their study in
Gulf of Mannar Coral reef environment. Bhadja and Kundu15, informed in their study
in the coastal Gujarat of Arabian Sea that the increment of temperature increases the
pH towards alkalinity. Although, this factor was not exhibited clearly in the figures,
due to rainwater and seawater mixing was taken place in different stages in different
location as well as at different depths. However, the stations Carbyns Cove exhibited
somewhat different than the other two stations with reference to the temperature and
pH may be due to the faster mixing of water mass that did not permit to equilibrium
with the temperature and pH which may show slight variation of trend among the
studied stations. The salinity variations noticed among the stations Chatham, North
Bay and Carbyns Cove, respectively, 4.64, 2.2 and 1.87 PSU also support the above
inferences strongly.
Over and above, the studied stations were also suggested that the change of pH
because of rainwater will take a period of 60 days to normalize to original status of
seawater, i. e. 2 months. It was evinced by the July lowering of pH which reached to
high alkaline side in the month of September and then September and October rain
influenced the water normalized during the month of November and January due to
the continuous rain. It also proved by the minor variation of time delay with reference
to pH which also marked clearly in the graph i. e. the surface water shows pH near to
lower alkaline region and bottom water (15 m) exhibited pH of high alkaline regions.
Moreover, in the case of November, this reversal i. e. surface to bottom has not been
noticed for pH. This may be due to the lesser input of land based litter fall and other
organic inputs because of continuous rain wash on the land surface and also due to the
leaching of carbonate sediments and rocks. This may have increased the availability
of Ca ions during this period which retained the alkalinity and due course of
normalization it will be maintained its original level. This inference was supported by
the findings of Lloret et al., 16 that flood waters from land surface had more influence
on organic carbon availability in the sea for volcanic islands due to intense desorption
or solubilisation of soil organic matter and its transfer into streams. Over and above,
Lloret et al.16, also reported that the DIC increases wherever the slope is steeper, due
to more weathering and dissolution of soil and rock.
The DOC concentration among the stations suggested that the average values of
Chatham exhibited highest concentration (86.59 to 106.19 µM/L) than the remaining
stations. This may be suggested that the organic carbon may be provided by the
anthropogenic inputs (waste from the fishery jetty, waste from the ship, etc.,) over and
above the natural inputs. This was supported by the fact that there was not a ND level
of reduction of DOC noticed in the study period. However such factor was not present
in the North Bay location. This may be due to not having input from the nearby
terrestrial environment and maintains the pristine environment.
Station Carbyns Cove exhibited comparatively lower level of DOC which suggested
that the anthropogenic input was comparatively low. It further supported the fact that
the inland waters may be provided only domestic waste i. e. no other activities like
shipping, fish landing, etc., was not available on this bank.
The DIC represented almost similar level in all the stations which may be inferred that
the input of inorganic carbon reached to these waters routed through atmospheric
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
45
mixing with seawater as an air-sea interaction, input routed through rainwater
dissolution of CO2 as well as leaching of carbonate in the terrestrial environment. This
inference was supported by the work of Willey et al.17, who reported that rain was an
important source of surface seawater carbon (90x 1012g C/yr) which is almost equal to
the input from river. Rogge et al., 18 Nunes and Pio19, and Sillanpaa et al.20, reported
that more than 80 of the urban aerosol contain carbonaceous materials which able to
provide elemental carbon and particulate organic carbon. Over and above, Butler21,
and Takahashi et al.22, reported that the dissolution of calcium carbonate increases
DIC concentration and latter breakdown of DIC into its specific components CO2(aq),
HCO3-and CO3-2 depends upon the pH, alkalinity and temperature of water. So, the
DIC input was noticed to be same in all the stations without much drastic variations in
its concentration leads to infer that the above factors have significance influences in
this seawater. The rainwater may be provided around 100 µM/L of DIC in this
environment. However, when comparing all the three stations, the lower average
concentration (102.81 to 135.06 µM/L) was noticed for the station North Bay and
other two stations had comparatively higher DIC concentrations (Chatham-121.50 to
138.19 µM/L and Carbyns Cove-122.81 to 128.81 µM/L) suggested that upto certain
level, anthropogenic activities were also provided DIC to these environments. That is
the movement of boats and ships may have provided exhaust smoke which may be
influenced in the station Chatham and vehicular transport happened very close to the
Carbyns Cove environment due to the famous tourist sport may be provided motor
exhaust inorganic carbon to these environments. Further, as reported by Schulz et
al.23, the DIC does not affect the total alkalinity and in turn it would not influence the
pH of the seawater. The above inferences was further supported by Suzuki and
Kawahata24, which states that if the organic carbon to DIC ration is greater than 0.60
the liberation of carbon will be less, where in the present study the ratio is between
0.76 to 0.84.
Moreover, the increase of DIC concentration during November inferred that ion
absorption from rainwater to seawater may take 30 to 60 days period i. e. in the month
of October rainfall brought DIC will be incorporated to seawater during the month of
November. This was supported by the Table 5 where the rain was high in the month
of October 2014 (18.4 mm), the DIC concentration noticed in the month of November
2015 (5.8 mm). Similarly, the lower level of DIC in the month of October 2014 may
be due to the fact that August and September exhibited lower rain fall (09.1 and
13.7mm, respectively). Mohan et al.25, also reported from the study area that five
months need to the physico-chemical parameters mixing from freshwater became as a
fully fledged seawater.
The rainfall data in 2014 between July to December 2014 suggested that there were
two sets of highest rainfall noticed in this period. They were during the month of July
and October i. e. 22.5 mm and 18.2 mm as monthly average. This data could be
interpreted with seawater temperature and pH which shows a very interesting feature
that the rainwater mixing does not lower the temperature of sea water immediately
and it takes minimum of one month to this process. It was very clearly proved in all
the figures (Fig. 2, 3 and 4) that temperature decreased from around 29.5°C during the
month of July to 28.0°C during the month of August. A similar trend was noticed in
P.M. Mohan et al
46
the month of October to November also support the fact that the time needed to
equilibrium the temperature of rainwater with seawater takes minimum of one month.
Further, this factor was supported by pH that during the high temperature real
rainwater pH (i. e. low alkalinity) was maintained by the seawater and it has taken
two months to reach equilibrium i. e. July to September. However, in the second
phase of monsoon i. e. North East, the real basic carbonate rocks undergo leaching
and provide DIC to seawater which was able to influence the seawater pH. This was
evinced by the month of September the pH moves through the low alkalinity region
along with high DIC values and delayed the process of equilibrium towards another
two more months i. e. the shift of lower alkalinity during the month of December and
then it started to normalize in the further periods.
Table 4: The Maximum Temperature, Average Temperature and Average Rainfall for
the study period.
Month
Maximum Temperature
°C
Average Temperature
°C
Average Rainfall
mm
April-14
34. 3
29. 8
00. 0
May-14
32. 3
29. 0
07. 3
June-14
30. 6
28. 1
16. 7
July-14
29. 8
27. 4
22. 5
August-14
30. 1
27. 5
09. 1
September-14
30. 0
27. 0
13. 7
October-14
30. 5
27. 5
18. 4
November-14
30. 8
28. 0
05. 8
December-14
31. 0
28. 4
00. 5
CONCLUSION
Based on the present study the following factors were concluded. They are:
1. Temperature increment would not decrease the pH towards the acidification
because as per the physical law the increase in temperature decreases the
dissolution and retention capacity of gas by water.
2. Organic carbon may be 50 to 150 µM/L level available in these waters.
3. Rainwater may be provided around 100 µM/L of DIC in this study area.
4. The leaching of carbonate soil and rocks may be provided around 300 µM/L of
DIC in these waters.
5. The seasonal DOC and DIC available in the present study were able to
influences the pH for a shorter period and it will be normalized by the biological
processes in due course of time.
Dissolved Organic (DOC) And Inorganic Carbon (DIC)
47
ACKNOWLEDGEMENT
The authors are acknowledging the Indian Institute of Tropical Meteorology (IITMMoES), Pune, for the fund provided for this study. The authors also thank the
Authorities of Pondicherry University for extending their facilities for this work.
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