Dissolved carbon dioxide and methane from mangrove associated
waters of Andaman Islands, India
Neetha V. 1, Ramesh R. 1, Jennifer Divia 1, Barnes J. 2, Purvaja R. 1, Upstill Goddard R.C. 2
Introduction
»Continental shelves cover 8% of »However their sediments and
ocean surface but play a major o v e r l y i n g w a t e r s a r e n e t
heterotrophic.
role in marine biogeochemistry.
»Measurements carried out over
»They are a net source of CO2 and 24hrs and in adjacent inshore
CH4 especially in estuaries, coral surface water transects.
r e e f s , s a l t m a r s h e s a n d »Results of seasonal distribution
of pCO2, dissolved CH4, dissolved
mangroves.
»Mangrove plant biomass is O2, total Alkalinity (TAlk) and
dissolved inorganic carbon (DIC)
considered to be net autotrophic.
are presented here.
Materials and Methods
» pCO2 calculated using pH and TAlk
using CO2 sys software
(Frankignoulle and Borges 2001,
Millero et al 2006)
»Dissolved CH4 by single phase
equilibration gas chromatography
(Upstill Goddard et al 1996).
»Talk measured by Gran (1952)
titration.
»In situ Salinity, temperature,
turbidity, diss. O2 - Horiba W 22.2
» Wind speed (anemometer - Lutron
Lm8000)
» Water current (open channel flow
meter - Valeport, UK)
» Flux F=kwLÄp, kw: gas transfer
velocity (derived using Clark et al
1995 and Borges et al 2004), L:
Ostwald sol. coeff. Äp: partial pr. diff.
across air-water interface
Fig. 1: Locations of Kalighat and Wright Myo tidal surveys and the surface water transects:
TI, Kalighat to Mayabander; TII, Mayabander to Interview Island via Austin creek;
TIII, Wright Myo to the Andaman Sea; TIV, Wandoor National Park to Chidiyatapu.
a
b
Fig. 3. TAlk vs Salinity during the inshore water
transects during: a) dry season (April 2005 and
2006); b) wet season (August 2005 and 2006).
Fig 2: Tidal variation of water height (filled circles), salinity (open triangles), pCO2 (open squares), dissolved CH4 (open diamonds), percent O2 saturation (open circles), DIC (open
squares) and TAlk (open circles) at Kalighat and (2005) Wright Myo (2005-2006) creeks during (a): April 2006 (dry season); (b), August 2006 (wet season). Shaded areas correspond
to hours of darkness. Tidal heights are all relative to the mean of the lowest and highest tidal elevations observed during the survey.
Fig. 4: Talk vs DIC during the tidal surveys at Kalighat
and Wright Myo creeks.
Conclusions
pCO2 higher during the wet seasons at KGC due to enhanced availability of organic matter leading to higher CO2 produced through respiration.
Absence of seasonal variation for dissolved CH4 indicating negligible thermal effect on CH4 production.
Tidal effect caused by tidal pumping wherein sediment pore waters depleted in O2 and enriched in by products of organic matter oxidation
seep into creek waters.
TAlk and DIC relationships reveal that aerobic oxidation and sulphate reduction are the major mechanisms that contribute to organic matter
oxidation in mangrove sediments.
Overall pCO2 and dissolved CH4 decreased with salinity in all transects, indicating that creek waters significantly influence the distribution of
these gases in nearshore waters.
4
-2 -1
Estimated mean tidal creek fluxes calculated using parameterizations of Clark et al 1995 and Borges et al 2004 are ~2.3 - 17.3 x 10 umolm d
2
-2 -1
CO2 and ~1.13 - 4.65 x 10 umolm d CH4.
These estimates are within previously published ranges for mangrove ecosystems.
Present study does no include adjacent creek open water area, other mechanisms of CO2 and CH4 transfer such as crab burrows, plant
pneumatophores or ebullition rates in which these gases pass directly to atmosphere without dissolving in water and therefore the estimated
emission rates could be underestimated.
Improving current understanding of mangrove carbon dynamics is important for predicting system response to large scale changes such as
clearance or replanting.
1
* Institute for Ocean Management, Anna University, Chennai 600 025
2
Ocean Research Group, School of Marine Science and Technology, New Castle University, New Castle upon Tyne, UK
Reference:
Borges, A.V., Vanderborght, J. P., Schiettecatte,
L-S., Gazeau, F., Ferrón, S., Delille, B.,
Frankignoulle, M., 2004. Estuaries 27, 593-603.
Clark, J.F., Schlosser, P., Wanninkhof, R.,
Simpson, H. J., Schuster, W. S. F., Ho, D. T.,
1995. Geophysical Research Letters 22, 93-96.
Frankignoulle, M., Borges, A. V., 2001. Aquatic
Geochemistry 7, 267-273.
Gran G., 1952. Analyst 77, 661-671.
Upstill-Goddard, R. C., Rees, A. P., Owens, N. J.
P., 1996. Deep Sea Research, 43, 1669-1682.
Acknowledgement:
University Grants Commission (UGC), Government of India,
for facilitating a Junior Research Fellowship (PhD) in support
of Neetha V. Special thanks to Leverhulme Trust
(http://www.leverhulme.ac.uk/) for their financial support.