Coastal environments including estuaries fluxes CH 4.

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2 Methane is an atmospheric trace gas that contributes significantly to the greenhouse effect. Biogenic methane is produced exclusively by a group of strict anaerobes (methanogens) during methanogenesis. This process occurs in the sediments, in the interior of suspended particles and in the gutsof Et Estuarine marine organisms. Coastal environments including estuaries fluxes CH 4. Although data from tropical/sub-tropical estuaries are scarce, a few that are available suggest that CH 4 emissions from polluted tropical estuaries are up to 2 times greater than from unpolluted ones (Purvaja and Ramesh 2).

3 Gujarat is one of the most industrialised and urbanised states of India. Majority of these industries uses near by rivers for there daily consumption of water and discharges their waste water into rivers. This pollution load is carried with the river and reaches to the estuary. Tapi is major river passing through the state of Gujarat. Majority of industries i in vicinity iiit of it,arechemical and petrochemical based and hence has potential to alters nutrients composition. Data on the Methane and other green house gases are scared from the Tapi estuary. Present study was attempt to characterize the Dissolved methane Present study was attempt to characterize the Dissolved methane concentration in relation to important nutrient gradients in surface waters of tapi estuary, Gujarat.

4 Tapi is major Perennial River of the west coast of the India, passes through hilly terrain of the Western Ghats before entering coastal alluvial plains of Gujarat to meet Gulf of Khambhat near Dumas. The shallow and wide lower segment of the river exhibits characteristics of a typical estuary with strong current associated with significantly high tidal influence upto 25 km up stream. Two stations have been identified for the present study, ONGC Bridge (21º 8 N Lat and 72º 44 E Lon) at the upper reaches Dumas (21º 6 N Lat and 72º 42 E Lon) at lower reaches of the estuary.

5 Dumas ONGC Bridge

6 Dissolved methane e Surface water samples for dissolved CH 4 analyses were collected monthly (January-8 to July-8) in 1 ml serum bottles, inoculated with.1 ml of saturated HgCl 2, sealed and stored in the dark in an icebox. In laboratory, 5 ml sub-sample was transferred to 1 ml sealed vials pre-flushed with ultra pure N 2 and shaken vigorously to equilibrate for 1 minutes. Methane concentration in headspace gas was determined using Perkin Elmer Auto system XL gas chromatograph (GC) equipped with flame ionization detector (FID). Temperature setting was 1 C, 45 C and 15 C for oven, column and dt detector, t respectively. Physico-chemical parameters Total organic carbon (TOC) in surface water samples was measured using total organic carbon analyzer (Shimadzu, TOC-VCSN) by catalytically aided combustion oxidation at 68 C. Surface water samples from sites were collected with a wide mouth inert polyethylene bottle and analyzed within 24 hrs using standard methods (APHA, 1998) for salinity, phosphate, p nitrate and sulphate. Dissolved oxygen was estimated on site. Correlation analysis between parameters and one-way Analysis of Variance (ANOVA) were employed for the data set.

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9 Dissolved Met thane (nmol/l) Jan Feb Mar Apr May June July Station ONGC Bridge Station Dumas The mean Dissolved CH 4 concentration for all samples at station ONGC was nmol/l and at Station Dumas was nmol/l. In, monsoon months methane concentration ti and other parameters was higherh at the upper reaches than lower reaches. Methane concentration showed slight Spatial Variation (p =.15).

10 Dissolv ved Methane( nmol/l) Salinity Station ONGC Bridge Station Dumas Salinity in the estuary was observed in the range of 5.38 ppt at ONGC to ppt Dumas in January.

11 Dissolved Met thane (nmol/l) Jan Feb Mar Apr May June July Dissolved methane TOC Dissolved Met thane (nmol/l) Jan Feb Mar Apr May June July Dissolved methane TOC ONGC Bridge Dumas Total organic carbon in surface water observed in the range of 8.87 mg/l to mg/l. TOC Found higher at Upper reaches than Lower reaches. TOC Found positively correlated with Methane concentration (r 2 =.31).

12 Dissolved Meth hane (nmol/l) Jan Feb Mar Apr May June July (ml/l) DO Dissolved Meth hane (nmol/l) Jan Feb Mar Apr May June July DO (ml/l) Dissolved methane (nmol/l) DO (ml/l) Dissolved methane (nmol/l) DO (ml/l) ONGC Bridge Dumas Dissolved Oxygen concentration showed marked seasonal variation with the range of 3.37 ml/l to 7.87 ml/ l. Dissolved Oxygen was found higher at Dumas than ONGC Bridge. Dissolved oxygen expressed negative correlation with methane concentration (r 2 =.15)

13 Dissolved methane and Nutrient Gradients Jan Feb Mar Apr May June July Phosphate (umol/l) Nitrate (umol/l) Dissolved Me thane (nmol/l) Sulphate mmol/l Dissolved methane (nmol/l) Jan Feb Mar Apr May June July Phosphate (umol/l) Sulphate mmol/l 12 ) Dissolved Methane (nmol/l) Nitrate (umol/l) Dissolved methane (nmol/l) ONGC Bridge Dumas Phosphate values varied from.4 µmol/l at Upper estuary (ONGC Bridge) to 3.46 µmol/l at lower estuary (Dumas). Dissolved sulphate was observed in the range of 1.3 to 3.43 mmol/l and found higher at lower reaches than in upper reaches and showed negative correlation (r 2 =.2).

14 Dissolved methane concentration in surface waters of Tapi estuary was higher at upper reaches than the lower reaches. Methane concentration varies temporally and found higher in summer months. Methane concentration has negative correlation with the nutrients (phosphate, nitrate and sulphate) and Dissolved oxygen. Methane concentration showed positive correlation with total organic carbon.

15 Authors are highly thankful to Ocean Science and Technology Cell (OSTC), Bhavnagar University, Ministry of Earth Sciences (MoES), New Delhi India for financiali assistance. Authors are also thankful to Mr. Tiwari for analysis of methane and total organic carbon by Gas Chromatography and Total Organic Carbon analyzer, respectively, in Sophisticated Instrumentation Center for Advanced Research and Testing (SICART), Vallabh Vidyanagar. Gujarat.

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